String-源码阅读

package com.string;

import java.io.ObjectStreamField;
import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Formatter;
import java.util.Locale;
import java.util.Objects;
import java.util.StringJoiner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;
/**
 *
 * 功能描述: String 源码解析
 *
 * 本源码基于JDK 1.8
 *
 * @param:
 * @return:
 * @auther: csh
 * @date: 2022/9/4 3:54 下午
 */
public  class StringSource
        implements java.io.Serializable, Comparable<String>, CharSequence {
    /** 定义字符字类型值数组*/
    private final char value[];

    /**缓存字符串的哈希码 */
    private int hash; // Default to 0

    /** 序列化id */
    private static final long serialVersionUID = -6849794470754667710L;

    /**
     * Class String is special cased within the Serialization Stream Protocol.
     * String类在序列化流协议中是特殊的。貌似没找着使用地方。
     *
     * A String instance is written into an ObjectOutputStream according to
     * <a href="{@docRoot}/../platform/serialization/spec/output.html">
     * Object Serialization Specification, Section 6.2, "Stream Elements"</a>
     */
    private static final ObjectStreamField[] serialPersistentFields =
            new ObjectStreamField[0];

    /**
     * Initializes a newly created {@code String} object so that it represents
     * an empty character sequence. Note that use of this constructor is
     * unnecessary since Strings are immutable.
     *
     * 初始化String的值为""
     */
    public String() {
        this.value = "".value;
    }

    /**
     * Initializes a newly created {@code String} object so that it represents
     * the same sequence of characters as the argument; in other words, the
     * newly created string is a copy of the argument string. Unless an
     * explicit copy of {@code original} is needed, use of this constructor is
     * unnecessary since Strings are immutable.
     *
     * @param  original
     * A {@code String}
     *
     * 通过 new String("xx") 构建方法创建的值，并且会计算该值的哈希码
     */
    public String(String original) {
        this.value = original.value;
        this.hash = original.hash;
    }

    /**
     * Allocates a new {@code String} so that it represents the sequence of
     * characters currently contained in the character array argument. The
     * contents of the character array are copied; subsequent modification of
     * the character array does not affect the newly created string.
     *
     * @param  value
     * The initial value of the string
     * 通过字符数组创建String
     */
    public String(char value[]) {
        //通过arrays.copyOf进行赋值，传长度是为了方便在new chare(length)创建长度
        this.value = Arrays.copyOf(value, value.length);
    }

    /**
     * Allocates a new {@code String} that contains characters from a subarray
     * of the character array argument. The {@code offset} argument is the
     * index of the first character of the subarray and the {@code count}
     * argument specifies the length of the subarray. The contents of the
     * subarray are copied; subsequent modification of the character array does
     * not affect the newly created string.
     *
     * @param  value
     * Array that is the source of characters
     *
     * @param  offset
     * The initial offset
     *
     * @param  count
     * The length
     *
     * @throws  IndexOutOfBoundsException
     * If the {@code offset} and {@code count} arguments index
     * characters outside the bounds of the {@code value} array
     * String 构建方法创建之一
     * char value[] 字符数组 就要是内容
     * int offset 偏移量
     * int count 数量
     */
    public String(char value[], int offset, int count) {
        //小于0直接抛出数组角标越界
        if (offset < 0) {
            throw new StringIndexOutOfBoundsException(offset);
        }
        //数量小于或等于0
        if (count <= 0) {
            //同样抛出数组角标越界
            if (count < 0) {
                throw new StringIndexOutOfBoundsException(count);
            }
            //如果偏移量小于等于值长度，重新将当前的内容赋值为空，并返回。
            if (offset <= value.length) {
                this.value = "".value;
                return;
            }
        }
        // Note: offset or count might be near -1>>>1.
        //向右移一位减去数量
        if (offset > value.length - count) {
            throw new StringIndexOutOfBoundsException(offset + count);
        }
        //复制区间
        this.value = Arrays.copyOfRange(value, offset, offset+count);
    }

    /**
     *
     * @param codePoints 内容
     * @param offset 偏移量
     * @param count 长度
     */
    public String(int[] codePoints, int offset, int count) {
        //小于0抛出异常
        if (offset < 0) {
            throw new StringIndexOutOfBoundsException(offset);
        }
        //长度小于等于0
        if (count <= 0) {
            //小于0跑出异常
            if (count < 0) {
                throw new StringIndexOutOfBoundsException(count);
            }
            //如果小于内容长度小于偏移量将值赋为"" 并且返回
            if (offset <= codePoints.length) {
                this.value = "".value;
                return;
            }
        }
        // Note: offset or count might be near -1>>>1.
        //向右移一位减去数量
        if (offset > codePoints.length - count) {
            throw new StringIndexOutOfBoundsException(offset + count);
        }
        //偏移量加上数量
        final int end = offset + count;
        // Pass 1: Compute precise size of char[]
        int n = count;
        //计算char的精确大小[]
        for (int i = offset; i < end; i++) {
            int c = codePoints[i];
            if (Character.isBmpCodePoint(c))
                continue;
            else if (Character.isValidCodePoint(c))
                n++;
            else throw new IllegalArgumentException(Integer.toString(c));
        }

        // Pass 2:分配并填充char[]
        final char[] v = new char[n];
        for (int i = offset, j = 0; i < end; i++, j++) {
            int c = codePoints[i];
            if (Character.isBmpCodePoint(c))
                v[j] = (char)c;
            else
                Character.toSurrogates(c, v, j++);
        }

        this.value = v;
    }

    /**该方法已删除标识 **/
    @Deprecated
    public String(byte ascii[], int hibyte, int offset, int count) {
        checkBounds(ascii, offset, count);
        char value[] = new char[count];

        if (hibyte == 0) {
            for (int i = count; i-- > 0;) {
                value[i] = (char)(ascii[i + offset] & 0xff);
            }
        } else {
            hibyte <<= 8;
            for (int i = count; i-- > 0;) {
                value[i] = (char)(hibyte | (ascii[i + offset] & 0xff));
            }
        }
        this.value = value;
    }

    /**
     * 该方法已快删除
     */
    @Deprecated
    public String(byte ascii[], int hibyte) {
        this(ascii, hibyte, 0, ascii.length);
    }

    /**
     * 检查异常
     * @param bytes 字节
     * @param offset 偏移量
     * @param length 长度
     */
    private static void checkBounds(byte[] bytes, int offset, int length) {
        if (length < 0)
            throw new StringIndexOutOfBoundsException(length);
        if (offset < 0)
            throw new StringIndexOutOfBoundsException(offset);
        if (offset > bytes.length - length)
            throw new StringIndexOutOfBoundsException(offset + length);
    }

    /**
     * 指定字符集赋值
     * @param bytes 字节数组（内容）
     * @param offset 偏移量
     * @param length 长度
     * @param charsetName 字符集编码名称默认为：ISO-8859-1
     * @throws UnsupportedEncodingException
     */
    public String(byte bytes[], int offset, int length, String charsetName)
            throws UnsupportedEncodingException {
        //为空直接抛出异常
        if (charsetName == null)
            throw new NullPointerException("charsetName");
        //检查数据格式
        checkBounds(bytes, offset, length);
        //将字符集转换的赋值
        this.value = StringCoding.decode(charsetName, bytes, offset, length);
    }

    /**
     * 不带字符集赋值（同上类似）
     * @param bytes
     * @param offset
     * @param length
     * @param charset
     */
    public String(byte bytes[], int offset, int length, Charset charset) {
        if (charset == null)
            throw new NullPointerException("charset");
        checkBounds(bytes, offset, length);
        this.value = StringCoding.decode(charset, bytes, offset, length);
    }

    /**
     * 指定字符集赋值 调用以上
     * @param bytes
     * @param charsetName
     * @throws UnsupportedEncodingException
     */
    public String(byte bytes[], String charsetName)
            throws UnsupportedEncodingException {
        this(bytes, 0, bytes.length, charsetName);
    }

    /**
     * 指定字符集赋值创建的构建方法
     * @param bytes
     * @param charset
     */
    public String(byte bytes[], Charset charset) {
        this(bytes, 0, bytes.length, charset);
    }

    /**
     * 不带字符集的构建方法
     * @param bytes
     * @param offset
     * @param length
     */
    public String(byte bytes[], int offset, int length) {
        checkBounds(bytes, offset, length);
        this.value = StringCoding.decode(bytes, offset, length);
    }

    /**
     * 字节数组构建方法
     * @param bytes 字节列表
     */
    public String(byte bytes[]) {
        this(bytes, 0, bytes.length);
    }

    /**
     * 通过StringBuffer创建的构建方法 线程安全
     * @param buffer
     */
    public String(StringBuffer buffer) {
        //同步锁
        synchronized(buffer) {
            this.value = Arrays.copyOf(buffer.getValue(), buffer.length());
        }
    }

    /**
     * 通过StringBuilder 创建的构建方法 非线程安全
     * @param builder
     */
    public String(StringBuilder builder) {
        this.value = Arrays.copyOf(builder.getValue(), builder.length());
    }

    /**
     * 通过 字节数组创建string
     * @param value
     * @param share
     */
    String(char[] value, boolean share) {
        // assert share : "unshared not supported";
        this.value = value;
    }

    /**
     * 返回当前字符串的长度
     * @return
     */
    public int length() {
        return value.length;
    }

    /**
     * 判断当前的字符串是否为空，以lenth
     * @return
     */
    public boolean isEmpty() {
        return value.length == 0;
    }

    /**
     * 获取字符串的位数的char数据
     * @param index 坐标
     * @return
     */
    public char charAt(int index) {
        //小于0或长度大于字符串长度抛出 数组角标越界
        if ((index < 0) || (index >= value.length)) {
            throw new StringIndexOutOfBoundsException(index);
        }
        return value[index];
    }

    /**
     * 返回指定位置的字符转成的int
     * @param index
     * @return
     */
    public int codePointAt(int index) {
        if ((index < 0) || (index >= value.length)) {
            throw new StringIndexOutOfBoundsException(index);
        }
        return Character.codePointAtImpl(value, index, value.length);
    }

    /**
     *
     * @param index
     * @return 获取当前位置前一位的字符的int
     */
    public int codePointBefore(int index) {
        int i = index - 1;
        if ((i < 0) || (i >= value.length)) {
            throw new StringIndexOutOfBoundsException(index);
        }
        return Character.codePointBeforeImpl(value, index, 0);
    }

    /**
     * 返回此字符串的指定文本范围内的Unicode码位数。
     * @param beginIndex
     * @param endIndex
     * @return
     */
     public int codePointCount(int beginIndex, int endIndex) {
        if (beginIndex < 0 || endIndex > value.length || beginIndex > endIndex) {
            throw new IndexOutOfBoundsException();
        }
        return Character.codePointCountImpl(value, beginIndex, endIndex - beginIndex);
    }

    /**
     * 返回此String中的索引，该索引与给定索引的偏移量为codePointOffset代码点。
     * @param index
     * @param codePointOffset
     * @return
     */
    public int offsetByCodePoints(int index, int codePointOffset) {
        if (index < 0 || index > value.length) {
            throw new IndexOutOfBoundsException();
        }
        return Character.offsetByCodePointsImpl(value, 0, value.length,
                index, codePointOffset);
    }

    /**
     * Copy characters from this string into dst starting at dstBegin.
     * This method doesn't perform any range checking.
     * 从dstBegin开始将字符从该字符串复制到dst中。
     */
    void getChars(char dst[], int dstBegin) {
        System.arraycopy(value, 0, dst, dstBegin, value.length);
    }

    /**
     * 从srcBegin开始将字符从该字符串复制到dst中。
     * @param srcBegin
     * @param srcEnd
     * @param dst
     * @param dstBegin
     */
    public void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin) {
        //小于0跑出数组角标越界
        if (srcBegin < 0) {
            throw new StringIndexOutOfBoundsException(srcBegin);
        }
        //srcEnd大于数据最长抛出异常
        if (srcEnd > value.length) {
            throw new StringIndexOutOfBoundsException(srcEnd);
        }
        //开始大于结束 抛出异常
        if (srcBegin > srcEnd) {
            throw new StringIndexOutOfBoundsException(srcEnd - srcBegin);
        }
        //系统复制
        System.arraycopy(value, srcBegin, dst, dstBegin, srcEnd - srcBegin);
    }

    /**
     * 将此字符串中的字符复制到目标字节数组中。每个字节接收对应字符的8个低阶位。
     * 每个字符的8个高阶位不会被复制，也不会以任何方式参与传输。
     * @param srcBegin
     * @param srcEnd
     * @param dst
     * @param dstBegin
     */
    @Deprecated
    public void getBytes(int srcBegin, int srcEnd, byte dst[], int dstBegin) {
        if (srcBegin < 0) {
            throw new StringIndexOutOfBoundsException(srcBegin);
        }
        if (srcEnd > value.length) {
            throw new StringIndexOutOfBoundsException(srcEnd);
        }
        if (srcBegin > srcEnd) {
            throw new StringIndexOutOfBoundsException(srcEnd - srcBegin);
        }
        Objects.requireNonNull(dst);

        int j = dstBegin;
        int n = srcEnd;
        int i = srcBegin;
        char[] val = value; /* avoid getfield opcode */

        while (i < n) {
            dst[j++] = (byte)val[i++];
        }
    }

    /**
     * 获取指定字符集的字节数组
     */
    public byte[] getBytes(String charsetName)
            throws UnsupportedEncodingException {
        if (charsetName == null) throw new NullPointerException();
        return StringCoding.encode(charsetName, value, 0, value.length);
    }

    /**
     * 使用给定字符集将该String编码为一个字节序列，并将结果存储到一个新的字节数组中。
     * @param charset
     * @return
     */
    public byte[] getBytes(Charset charset) {
        if (charset == null) throw new NullPointerException();
        return StringCoding.encode(charset, value, 0, value.length);
    }

    /**
     * 将所有数数以字节数组方式返回
     * @return
     */
    public byte[] getBytes() {
        return StringCoding.encode(value, 0, value.length);
    }

    /**
     * 对于两个值内容是否一致。
     * @param anObject
     * @return
     */
    public boolean equals(Object anObject) {
        //如果连内存地址一致直接返回true
        if (this == anObject) {
            return true;
        }
        //判断是否为字符串类型
        if (anObject instanceof String) {
            String anotherString = (String)anObject;
            int n = value.length;
            if (n == anotherString.value.length) {
                char v1[] = value;
                char v2[] = anotherString.value;
                int i = 0;
                //循环对比每一位，如果都一样返回true，反之存在一位不一样返回false
                while (n-- != 0) {
                    if (v1[i] != v2[i])
                        return false;
                    i++;
                }
                return true;
            }
        }
        //默认返回false，所以这里也要注意，仅能对比String类型字符串，这里有个搞，如果你传进来是一个integer也是oK但是判断是直接走false
        return false;
    }

    /**
     * 通过内容方法是否一致方法
     * @param sb
     * @return
     */
    public boolean contentEquals(StringBuffer sb) {
        return contentEquals((CharSequence)sb);
    }

    /**
     * 私有方法 不是同步锁方式对比内容
     * @param sb
     * @return
     */
    private boolean nonSyncContentEquals(AbstractStringBuilder sb) {
        char v1[] = value;
        char v2[] = sb.getValue();
        int n = v1.length;
        if (n != sb.length()) {
            return false;
        }
        for (int i = 0; i < n; i++) {
            if (v1[i] != v2[i]) {
                return false;
            }
        }
        return true;
    }

    /**
     * 对比内容是否一致方法 安全方法
     * @param cs
     * @return
     */
    public boolean contentEquals(CharSequence cs) {
        // Argument is a StringBuffer, StringBuilder
        //判断是否为builder的类型
        if (cs instanceof AbstractStringBuilder) {
            //判断是否为StringBuffer类型
            if (cs instanceof StringBuffer) {
                //通过同步锁进行匹配
                synchronized(cs) {
                    return nonSyncContentEquals((AbstractStringBuilder)cs);
                }
            } else {
                //不是StringBuffer类型 不加锁判断
                return nonSyncContentEquals((AbstractStringBuilder)cs);
            }
        }
        // 字符串类型直接调用equals
        if (cs instanceof String) {
            return equals(cs);
        }
        // Argument is a generic CharSequence
        char v1[] = value;
        int n = v1.length;
        //都不是则判断长度是否不一致
        if (n != cs.length()) {
            return false;
        }
        //如果长度判断一样，最后通过这个来匹配每一位上面的字符是否一样，如果一样则返回true，否则就是false
        for (int i = 0; i < n; i++) {
            if (v1[i] != cs.charAt(i)) {
                return false;
            }
        }
        return true;
    }

    /**
     * 不区分大小对比内容
     * @param anotherString 内容
     * @return
     */
    public boolean equalsIgnoreCase(String anotherString) {
        return (this == anotherString) ? true
                : (anotherString != null)
                && (anotherString.value.length == value.length)
                && regionMatches(true, 0, anotherString, 0, value.length);
    }

    /**
     * Compares two strings lexicographically.
     * The comparison is based on the Unicode value of each character in
     * the strings. The character sequence represented by this
     * {@code String} object is compared lexicographically to the
     * character sequence represented by the argument string. The result is
     * a negative integer if this {@code String} object
     * lexicographically precedes the argument string. The result is a
     * positive integer if this {@code String} object lexicographically
     * follows the argument string. The result is zero if the strings
     * are equal; {@code compareTo} returns {@code 0} exactly when
     * the {@link #equals(Object)} method would return {@code true}.
     * <p>
     * This is the definition of lexicographic ordering. If two strings are
     * different, then either they have different characters at some index
     * that is a valid index for both strings, or their lengths are different,
     * or both. If they have different characters at one or more index
     * positions, let <i>k</i> be the smallest such index; then the string
     * whose character at position <i>k</i> has the smaller value, as
     * determined by using the &lt; operator, lexicographically precedes the
     * other string. In this case, {@code compareTo} returns the
     * difference of the two character values at position {@code k} in
     * the two string -- that is, the value:
     * <blockquote><pre>
     * this.charAt(k)-anotherString.charAt(k)
     * </pre></blockquote>
     * If there is no index position at which they differ, then the shorter
     * string lexicographically precedes the longer string. In this case,
     * {@code compareTo} returns the difference of the lengths of the
     * strings -- that is, the value:
     * <blockquote><pre>
     * this.length()-anotherString.length()
     * </pre></blockquote>
     *
     * @param   anotherString the {@code String} to be compared.
     * @return  the value {@code 0} if the argument string is equal to
     * this string; a value less than {@code 0} if this string
     * is lexicographically less than the string argument; and a
     * value greater than {@code 0} if this string is
     * lexicographically greater than the string argument.
     */
    public int compareTo(String anotherString) {
        int len1 = value.length;
        int len2 = anotherString.value.length;
        int lim = Math.min(len1, len2);
        char v1[] = value;
        char v2[] = anotherString.value;

        int k = 0;
        while (k < lim) {
            char c1 = v1[k];
            char c2 = v2[k];
            if (c1 != c2) {
                return c1 - c2;
            }
            k++;
        }
        return len1 - len2;
    }

    /**
     * A Comparator that orders {@code String} objects as by
     * {@code compareToIgnoreCase}. This comparator is serializable.
     * <p>
     * Note that this Comparator does <em>not</em> take locale into account,
     * and will result in an unsatisfactory ordering for certain locales.
     * The java.text package provides <em>Collators</em> to allow
     * locale-sensitive ordering.
     *
     * @see     java.text.Collator#compare(String, String)
     * @since   1.2
     */
    public static final Comparator<String> CASE_INSENSITIVE_ORDER
            = new CaseInsensitiveComparator();
    private static class CaseInsensitiveComparator
            implements Comparator<String>, java.io.Serializable {
        // use serialVersionUID from JDK 1.2.2 for interoperability
        private static final long serialVersionUID = 8575799808933029326L;

        public int compare(String s1, String s2) {
            int n1 = s1.length();
            int n2 = s2.length();
            int min = Math.min(n1, n2);
            for (int i = 0; i < min; i++) {
                char c1 = s1.charAt(i);
                char c2 = s2.charAt(i);
                if (c1 != c2) {
                    c1 = Character.toUpperCase(c1);
                    c2 = Character.toUpperCase(c2);
                    if (c1 != c2) {
                        c1 = Character.toLowerCase(c1);
                        c2 = Character.toLowerCase(c2);
                        if (c1 != c2) {
                            // No overflow because of numeric promotion
                            return c1 - c2;
                        }
                    }
                }
            }
            return n1 - n2;
        }

        /** Replaces the de-serialized object. */
        private Object readResolve() { return CASE_INSENSITIVE_ORDER; }
    }

    /**
     * Compares two strings lexicographically, ignoring case
     * differences. This method returns an integer whose sign is that of
     * calling {@code compareTo} with normalized versions of the strings
     * where case differences have been eliminated by calling
     * {@code Character.toLowerCase(Character.toUpperCase(character))} on
     * each character.
     * <p>
     * Note that this method does <em>not</em> take locale into account,
     * and will result in an unsatisfactory ordering for certain locales.
     * The java.text package provides <em>collators</em> to allow
     * locale-sensitive ordering.
     *
     * @param   str the {@code String} to be compared.
     * @return  a negative integer, zero, or a positive integer as the
     * specified String is greater than, equal to, or less
     * than this String, ignoring case considerations.
     * @see     java.text.Collator#compare(String, String)
     * @since   1.2
     */
    public int compareToIgnoreCase(String str) {
        return CASE_INSENSITIVE_ORDER.compare(this, str);
    }

    /**
     * Tests if two string regions are equal.
     * <p>
     * A substring of this {@code String} object is compared to a substring
     * of the argument other. The result is true if these substrings
     * represent identical character sequences. The substring of this
     * {@code String} object to be compared begins at index {@code toffset}
     * and has length {@code len}. The substring of other to be compared
     * begins at index {@code ooffset} and has length {@code len}. The
     * result is {@code false} if and only if at least one of the following
     * is true:
     * <ul><li>{@code toffset} is negative.
     * <li>{@code ooffset} is negative.
     * <li>{@code toffset+len} is greater than the length of this
     * {@code String} object.
     * <li>{@code ooffset+len} is greater than the length of the other
     * argument.
     * <li>There is some nonnegative integer <i>k</i> less than {@code len}
     * such that:
     * {@code this.charAt(toffset + }<i>k</i>{@code ) != other.charAt(ooffset + }
     * <i>k</i>{@code )}
     * </ul>
     *
     * @param   toffset the starting offset of the subregion in this string.
     * @param   other the string argument.
     * @param   ooffset the starting offset of the subregion in the string
     * argument.
     * @param   len the number of characters to compare.
     * @return  {@code true} if the specified subregion of this string
     * exactly matches the specified subregion of the string argument;
     * {@code false} otherwise.
     */
    public boolean regionMatches(int toffset, String other, int ooffset,
                                 int len) {
        char ta[] = value;
        int to = toffset;
        char pa[] = other.value;
        int po = ooffset;
        // Note: toffset, ooffset, or len might be near -1>>>1.
        if ((ooffset < 0) || (toffset < 0)
                || (toffset > (long)value.length - len)
                || (ooffset > (long)other.value.length - len)) {
            return false;
        }
        while (len-- > 0) {
            if (ta[to++] != pa[po++]) {
                return false;
            }
        }
        return true;
    }

    /**
     * 测试两个字符串区域是否相等。
     * @param ignoreCase true转成大写 false小写
     * @param toffset
     * @param other
     * @param ooffset
     * @param len
     * @return
     */
    public boolean regionMatches(boolean ignoreCase, int toffset,
                                 String other, int ooffset, int len) {
        char ta[] = value;
        int to = toffset;
        char pa[] = other.value;
        int po = ooffset;
        // 注意:toffset、ooffset或len可能在-1>>>1附近。
        if ((ooffset < 0) || (toffset < 0)
                || (toffset > (long)value.length - len)
                || (ooffset > (long)other.value.length - len)) {
            return false;
        }
        //循环赋值
        while (len-- > 0) {
            char c1 = ta[to++];
            char c2 = pa[po++];
            if (c1 == c2) {
                continue;
            }
            if (ignoreCase) {
                // If characters don't match but case may be ignored,
                // try converting both characters to uppercase.
                // If the results match, then the comparison scan should
                // continue.
                //统一转成大写
                char u1 = Character.toUpperCase(c1);
                char u2 = Character.toUpperCase(c2);
                if (u1 == u2) {
                    continue;
                }
                // Unfortunately, conversion to uppercase does not work properly
                // for the Georgian alphabet, which has strange rules about case
                // conversion. So we need to make one last check before
                // exiting.
                if (Character.toLowerCase(u1) == Character.toLowerCase(u2)) {
                    continue;
                }
            }
            return false;
        }
        return true;
    }

    /**
     * 测试 指定位置开头是不是以 prefix开头的字符串
     * @param prefix
     * @param toffset
     * @return
     */
    public boolean startsWith(String prefix, int toffset) {
        char ta[] = value;
        int to = toffset;
        char pa[] = prefix.value;
        int po = 0;
        int pc = prefix.value.length;
        // Note: toffset might be near -1>>>1.
        if ((toffset < 0) || (toffset > value.length - pc)) {
            return false;
        }
        while (--pc >= 0) {
            if (ta[to++] != pa[po++]) {
                return false;
            }
        }
        return true;
    }

    /**
     * 测试是不是以某个字符串开头的 默认从0位开始
     * @param prefix
     * @return
     */
    public boolean startsWith(String prefix) {
        return startsWith(prefix, 0);
    }

    /**
     * 测试是不是由指定字符串结束 ，默认为长度-开头长度开始
     * @param suffix
     * @return
     */
    public boolean endsWith(String suffix) {
        return startsWith(suffix, value.length - suffix.value.length);
    }

    /**
     * 获取哈希码方法
     * @return
     */
    public int hashCode() {
        int h = hash;
        if (h == 0 && value.length > 0) {
            char val[] = value;

            for (int i = 0; i < value.length; i++) {
                h = 31 * h + val[i];
            }
            hash = h;
        }
        return h;
    }

    /**
     * 获取内容的指定位置
     * @param ch
     * @return
     */
    public int indexOf(int ch) {
        return indexOf(ch, 0);
    }

    /**
     * 从指定开始位置，获取第几位的坐标，如果换不到返回-1
     * @param ch
     * @param fromIndex
     * @return
     */
    public int indexOf(int ch, int fromIndex) {
        final int max = value.length;
        if (fromIndex < 0) {
            fromIndex = 0;
        } else if (fromIndex >= max) {
            // Note: fromIndex might be near -1>>>1.
            return -1;
        }

        if (ch < Character.MIN_SUPPLEMENTARY_CODE_POINT) {
            // handle most cases here (ch is a BMP code point or a
            // negative value (invalid code point))
            final char[] value = this.value;
            for (int i = fromIndex; i < max; i++) {
                if (value[i] == ch) {
                    return i;
                }
            }
            return -1;
        } else {
            return indexOfSupplementary(ch, fromIndex);
        }
    }

    /**
     * 用一个补充字符处理indexOf(罕见)调用。
     */
    private int indexOfSupplementary(int ch, int fromIndex) {
        if (Character.isValidCodePoint(ch)) {
            final char[] value = this.value;
            final char hi = Character.highSurrogate(ch);
            final char lo = Character.lowSurrogate(ch);
            final int max = value.length - 1;
            for (int i = fromIndex; i < max; i++) {
                if (value[i] == hi && value[i + 1] == lo) {
                    return i;
                }
            }
        }
        return -1;
    }

    /**
     * 返回指定字符最后一次出现的字符串中的索引。对于ch在0到0xFFFF(包括)范围内的值，返回的索引(以Unicode代码单位)是最大的值k.
     * @param ch
     * @return
     */
    public int lastIndexOf(int ch) {
        return lastIndexOf(ch, value.length - 1);
    }

    /**
     * 返回指定字符最后一次出现的字符串中的索引
     * @param ch
     * @param fromIndex
     * @return
     */
    public int lastIndexOf(int ch, int fromIndex) {
        if (ch < Character.MIN_SUPPLEMENTARY_CODE_POINT) {
            // handle most cases here (ch is a BMP code point or a
            // negative value (invalid code point))
            final char[] value = this.value;
            int i = Math.min(fromIndex, value.length - 1);
            for (; i >= 0; i--) {
                if (value[i] == ch) {
                    return i;
                }
            }
            return -1;
        } else {
            return lastIndexOfSupplementary(ch, fromIndex);
        }
    }

    /**
     * 用一个补充字符处理lastIndexOf(罕见的)调用。
     */
    private int lastIndexOfSupplementary(int ch, int fromIndex) {
        if (Character.isValidCodePoint(ch)) {
            final char[] value = this.value;
            char hi = Character.highSurrogate(ch);
            char lo = Character.lowSurrogate(ch);
            int i = Math.min(fromIndex, value.length - 2);
            for (; i >= 0; i--) {
                if (value[i] == hi && value[i + 1] == lo) {
                    return i;
                }
            }
        }
        return -1;
    }

    /**
     * 获取字符串在指定位置
     * @param str
     * @return
     */
    public int indexOf(String str) {
        return indexOf(str, 0);
    }

    /**
     * 指定位置开始寻找字符串位置。
     * @param str
     * @param fromIndex
     * @return
     */
    public int indexOf(String str, int fromIndex) {
        return indexOf(value, 0, value.length,
                str.value, 0, str.value.length, fromIndex);
    }

    /**
     * 同上作用。
     * @param source 来源数据
     * @param sourceOffset 来源偏移量
     * @param sourceCount 来源数量
     * @param target 目标内容
     * @param fromIndex 开始位置
     * @return
     */
    static int indexOf(char[] source, int sourceOffset, int sourceCount,
                       String target, int fromIndex) {
        return indexOf(source, sourceOffset, sourceCount,
                target.value, 0, target.value.length,
                fromIndex);
    }

    /**
     * 同上
     * @param source
     * @param sourceOffset
     * @param sourceCount
     * @param target
     * @param targetOffset
     * @param targetCount
     * @param fromIndex
     * @return
     */
    static int indexOf(char[] source, int sourceOffset, int sourceCount,
                       char[] target, int targetOffset, int targetCount,
                       int fromIndex) {
        if (fromIndex >= sourceCount) {
            return (targetCount == 0 ? sourceCount : -1);
        }
        if (fromIndex < 0) {
            fromIndex = 0;
        }
        if (targetCount == 0) {
            return fromIndex;
        }

        char first = target[targetOffset];
        int max = sourceOffset + (sourceCount - targetCount);

        for (int i = sourceOffset + fromIndex; i <= max; i++) {
            /* Look for first character. */
            if (source[i] != first) {
                while (++i <= max && source[i] != first);
            }

            /* Found first character, now look at the rest of v2 */
            if (i <= max) {
                int j = i + 1;
                int end = j + targetCount - 1;
                for (int k = targetOffset + 1; j < end && source[j]
                        == target[k]; j++, k++);

                if (j == end) {
                    /* Found whole string. */
                    return i - sourceOffset;
                }
            }
        }
        return -1;
    }

    /**
     * 获取字符串最后一位的位置
     * @param str
     * @return
     */
    public int lastIndexOf(String str) {
        return lastIndexOf(str, value.length);
    }

    /**
     * 指定开始位置，寻找字符串最后一个位置
     * @param str
     * @param fromIndex
     * @return
     */
    public int lastIndexOf(String str, int fromIndex) {
        return lastIndexOf(value, 0, value.length,
                str.value, 0, str.value.length, fromIndex);
    }

    /**
     * 同上
     * @param source 来源数据
     * @param sourceOffset 来源偏移量
     * @param sourceCount 来源数量
     * @param target 目标内容
     * @param fromIndex 开始位置
     * @return
     */
    static int lastIndexOf(char[] source, int sourceOffset, int sourceCount,
                           String target, int fromIndex) {
        return lastIndexOf(source, sourceOffset, sourceCount,
                target.value, 0, target.value.length,
                fromIndex);
    }

    /**
     * 最终定位的方法（获取字符串）
     * @param source
     * @param sourceOffset
     * @param sourceCount
     * @param target
     * @param targetOffset
     * @param targetCount
     * @param fromIndex
     * @return
     */
    static int lastIndexOf(char[] source, int sourceOffset, int sourceCount,
                           char[] target, int targetOffset, int targetCount,
                           int fromIndex) {
        /*
         * Check arguments; return immediately where possible. For
         * consistency, don't check for null str.
         */
        //来源数量减目标数量
        int rightIndex = sourceCount - targetCount;
        //开始小于0返回-1
        if (fromIndex < 0) {
            return -1;
        }
        //开始大于右边位置 将右边位置赋值给开始位置
        if (fromIndex > rightIndex) {
            fromIndex = rightIndex;
        }
        /* 如果目标数量为0返恩啊开始位置 */
        if (targetCount == 0) {
            return fromIndex;
        }

        int strLastIndex = targetOffset + targetCount - 1;
        char strLastChar = target[strLastIndex];
        int min = sourceOffset + targetCount - 1;
        int i = min + fromIndex;

        startSearchForLastChar:
        //循环 寻找
        while (true) {
            while (i >= min && source[i] != strLastChar) {
                i--;
            }
            //小于最小值返回-1
            if (i < min) {
                return -1;
            }
            int j = i - 1;
            int start = j - (targetCount - 1);
            int k = strLastIndex - 1;
            //循环判断
            while (j > start) {
                if (source[j--] != target[k--]) {
                    i--;
                    continue startSearchForLastChar;
                }
            }
            //最终返回开始位减去偏移量+1
            return start - sourceOffset + 1;
        }
    }

    /**
     * 从指定位置开始裁剪 比如 abc 输入 1只剩下 bc
     * @param beginIndex
     * @return
     */
    public String substring(int beginIndex) {
        if (beginIndex < 0) {
            throw new StringIndexOutOfBoundsException(beginIndex);
        }
        int subLen = value.length - beginIndex;
        if (subLen < 0) {
            throw new StringIndexOutOfBoundsException(subLen);
        }
        return (beginIndex == 0) ? this : new String(value, beginIndex, subLen);
    }

    /**
     * 指字开始和结束位置进行裁剪字符串
     * @param beginIndex
     * @param endIndex
     * @return
     */
    public String substring(int beginIndex, int endIndex) {
        if (beginIndex < 0) {
            throw new StringIndexOutOfBoundsException(beginIndex);
        }
        if (endIndex > value.length) {
            throw new StringIndexOutOfBoundsException(endIndex);
        }
        int subLen = endIndex - beginIndex;
        if (subLen < 0) {
            throw new StringIndexOutOfBoundsException(subLen);
        }
        return ((beginIndex == 0) && (endIndex == value.length)) ? this
                : new String(value, beginIndex, subLen);
    }

    /**
     * 指定开始和结束位置进行裁剪字符串，并返回字节数组
     * @param beginIndex
     * @param endIndex
     * @return
     */
    public CharSequence subSequence(int beginIndex, int endIndex) {
        return this.substring(beginIndex, endIndex);
    }

    /**
     * 拼接字符串到形成新的字符串 比如 abc+de = abcde
     * @param str
     * @return
     */
    public String concat(String str) {
        int otherLen = str.length();
        if (otherLen == 0) {
            return this;
        }
        int len = value.length;
        char buf[] = Arrays.copyOf(value, len + otherLen);
        str.getChars(buf, len);
        return new String(buf, true);
    }

    /**
     * 替换字符 注意：仅替换一位
     * @param oldChar 老字符
     * @param newChar 新字符
     * @return
     */
    public String replace(char oldChar, char newChar) {
        if (oldChar != newChar) {
            int len = value.length;
            int i = -1;
            char[] val = value; /* avoid getfield opcode */
            //循环替换 注意这里仅替换一位
            while (++i < len) {
                if (val[i] == oldChar) {
                    break;
                }
            }
            if (i < len) {
                char buf[] = new char[len];
                for (int j = 0; j < i; j++) {
                    buf[j] = val[j];
                }
                while (i < len) {
                    char c = val[i];
                    buf[i] = (c == oldChar) ? newChar : c;
                    i++;
                }
                return new String(buf, true);
            }
        }
        return this;
    }

    /**
     * 通过正规表达式方式进行匹配
     * @param regex
     * @return
     */
    public boolean matches(String regex) {
        return Pattern.matches(regex, this);
    }

    /**
     * 判断是否包含字符
     * @param s
     * @return
     */
    public boolean contains(CharSequence s) {
        return indexOf(s.toString()) > -1;
    }

    /**
     * 通过正则表达式方式替换首位字符串
     * @param regex
     * @param replacement
     * @return
     */
    public String replaceFirst(String regex, String replacement) {
        return Pattern.compile(regex).matcher(this).replaceFirst(replacement);
    }

    /**
     * 通过正式表达式方式替换所有匹配正式的字符串
     * @param regex
     * @param replacement
     * @return
     */
    public String replaceAll(String regex, String replacement) {
        return Pattern.compile(regex).matcher(this).replaceAll(replacement);
    }

    /**
     * 替换所有字符串并返回替换后的结果
     * @param target
     * @param replacement
     * @return
     */
    public String replace(CharSequence target, CharSequence replacement) {
        return Pattern.compile(target.toString(), Pattern.LITERAL).matcher(
                this).replaceAll(Matcher.quoteReplacement(replacement.toString()));
    }

    /**
     * 通过正式表达式方式进行分割
     * @param regex 表达式
     * @param limit 长度
     * @return
     */
    public String[] split(String regex, int limit) {
        /* fastpath if the regex is a
         (1)one-char String and this character is not one of the
            RegEx's meta characters ".$|()[{^?*+\\", or
         (2)two-char String and the first char is the backslash and
            the second is not the ascii digit or ascii letter.
         */
        char ch = 0;
        if (((regex.value.length == 1 &&
                ".$|()[{^?*+\\".indexOf(ch = regex.charAt(0)) == -1) ||
                (regex.length() == 2 &&
                        regex.charAt(0) == '\\' &&
                        (((ch = regex.charAt(1))-'0')|('9'-ch)) < 0 &&
                        ((ch-'a')|('z'-ch)) < 0 &&
                        ((ch-'A')|('Z'-ch)) < 0)) &&
                (ch < Character.MIN_HIGH_SURROGATE ||
                        ch > Character.MAX_LOW_SURROGATE))
        {
            int off = 0;
            int next = 0;
            boolean limited = limit > 0;
            ArrayList<String> list = new ArrayList<>();
            while ((next = indexOf(ch, off)) != -1) {
                if (!limited || list.size() < limit - 1) {
                    list.add(substring(off, next));
                    off = next + 1;
                } else { // last one
                    //assert (list.size() == limit - 1);
                    list.add(substring(off, value.length));
                    off = value.length;
                    break;
                }
            }
            // If no match was found, return this
            if (off == 0)
                return new String[]{this};

            // Add remaining segment
            if (!limited || list.size() < limit)
                list.add(substring(off, value.length));

            // Construct result
            int resultSize = list.size();
            if (limit == 0) {
                while (resultSize > 0 && list.get(resultSize - 1).length() == 0) {
                    resultSize--;
                }
            }
            String[] result = new String[resultSize];
            return list.subList(0, resultSize).toArray(result);
        }
        return Pattern.compile(regex).split(this, limit);
    }

    /**
     * 分割，从0位坐标开始
     * @param regex
     * @return
     */
    public String[] split(String regex) {
        return split(regex, 0);
    }

    /**
     * 将字符拼接到字符串后面。
     * @param delimiter
     * @param elements
     * @return
     */
    public static String join(CharSequence delimiter, CharSequence... elements) {
        Objects.requireNonNull(delimiter);
        Objects.requireNonNull(elements);
        // Number of elements not likely worth Arrays.stream overhead.
        StringJoiner joiner = new StringJoiner(delimiter);
        for (CharSequence cs: elements) {
            joiner.add(cs);
        }
        return joiner.toString();
    }

    /**
     * 同上类似
     * @param delimiter
     * @param elements
     * @return
     */
    public static String join(CharSequence delimiter,
                              Iterable<? extends CharSequence> elements) {
        Objects.requireNonNull(delimiter);
        Objects.requireNonNull(elements);
        StringJoiner joiner = new StringJoiner(delimiter);
        for (CharSequence cs: elements) {
            joiner.add(cs);
        }
        return joiner.toString();
    }

    /**
     * 将当前字符串转换成指定语言的小写字符串
     * @param locale
     * @return
     */
    public String toLowerCase(Locale locale) {
        if (locale == null) {
            throw new NullPointerException();
        }

        int firstUpper;
        final int len = value.length;

        /* Now check if there are any characters that need to be changed. */
        scan: {
            for (firstUpper = 0 ; firstUpper < len; ) {
                char c = value[firstUpper];
                if ((c >= Character.MIN_HIGH_SURROGATE)
                        && (c <= Character.MAX_HIGH_SURROGATE)) {
                    int supplChar = codePointAt(firstUpper);
                    if (supplChar != Character.toLowerCase(supplChar)) {
                        break scan;
                    }
                    firstUpper += Character.charCount(supplChar);
                } else {
                    if (c != Character.toLowerCase(c)) {
                        break scan;
                    }
                    firstUpper++;
                }
            }
            return this;
        }

        char[] result = new char[len];
        int resultOffset = 0; /* result may grow, so i+resultOffset
         * is the write location in result */

        /* Just copy the first few lowerCase characters. */
        System.arraycopy(value, 0, result, 0, firstUpper);

        String lang = locale.getLanguage();
        boolean localeDependent =
                (lang == "tr" || lang == "az" || lang == "lt");
        char[] lowerCharArray;
        int lowerChar;
        int srcChar;
        int srcCount;
        for (int i = firstUpper; i < len; i += srcCount) {
            srcChar = (int)value[i];
            if ((char)srcChar >= Character.MIN_HIGH_SURROGATE
                    && (char)srcChar <= Character.MAX_HIGH_SURROGATE) {
                srcChar = codePointAt(i);
                srcCount = Character.charCount(srcChar);
            } else {
                srcCount = 1;
            }
            if (localeDependent ||
                    srcChar == '\u03A3' || // GREEK CAPITAL LETTER SIGMA
                    srcChar == '\u0130') { // LATIN CAPITAL LETTER I WITH DOT ABOVE
                lowerChar = ConditionalSpecialCasing.toLowerCaseEx(this, i, locale);
            } else {
                lowerChar = Character.toLowerCase(srcChar);
            }
            if ((lowerChar == Character.ERROR)
                    || (lowerChar >= Character.MIN_SUPPLEMENTARY_CODE_POINT)) {
                if (lowerChar == Character.ERROR) {
                    lowerCharArray =
                            ConditionalSpecialCasing.toLowerCaseCharArray(this, i, locale);
                } else if (srcCount == 2) {
                    resultOffset += Character.toChars(lowerChar, result, i + resultOffset) - srcCount;
                    continue;
                } else {
                    lowerCharArray = Character.toChars(lowerChar);
                }

                /* Grow result if needed */
                int mapLen = lowerCharArray.length;
                if (mapLen > srcCount) {
                    char[] result2 = new char[result.length + mapLen - srcCount];
                    System.arraycopy(result, 0, result2, 0, i + resultOffset);
                    result = result2;
                }
                for (int x = 0; x < mapLen; ++x) {
                    result[i + resultOffset + x] = lowerCharArray[x];
                }
                resultOffset += (mapLen - srcCount);
            } else {
                result[i + resultOffset] = (char)lowerChar;
            }
        }
        return new String(result, 0, len + resultOffset);
    }

    /**
     * 转换为小写字符串
     * @return
     */
    public String toLowerCase() {
        return toLowerCase(Locale.getDefault());
    }

    /**
     * 将字符串转换为指定语言大写的字符串
     * @param locale
     * @return
     */
    public String toUpperCase(Locale locale) {
        if (locale == null) {
            throw new NullPointerException();
        }

        int firstLower;
        final int len = value.length;

        /* Now check if there are any characters that need to be changed. */
        scan: {
            for (firstLower = 0 ; firstLower < len; ) {
                int c = (int)value[firstLower];
                int srcCount;
                if ((c >= Character.MIN_HIGH_SURROGATE)
                        && (c <= Character.MAX_HIGH_SURROGATE)) {
                    c = codePointAt(firstLower);
                    srcCount = Character.charCount(c);
                } else {
                    srcCount = 1;
                }
                int upperCaseChar = Character.toUpperCaseEx(c);
                if ((upperCaseChar == Character.ERROR)
                        || (c != upperCaseChar)) {
                    break scan;
                }
                firstLower += srcCount;
            }
            return this;
        }

        /* result may grow, so i+resultOffset is the write location in result */
        int resultOffset = 0;
        char[] result = new char[len]; /* may grow */

        /* Just copy the first few upperCase characters. */
        System.arraycopy(value, 0, result, 0, firstLower);

        String lang = locale.getLanguage();
        boolean localeDependent =
                (lang == "tr" || lang == "az" || lang == "lt");
        char[] upperCharArray;
        int upperChar;
        int srcChar;
        int srcCount;
        for (int i = firstLower; i < len; i += srcCount) {
            srcChar = (int)value[i];
            if ((char)srcChar >= Character.MIN_HIGH_SURROGATE &&
                    (char)srcChar <= Character.MAX_HIGH_SURROGATE) {
                srcChar = codePointAt(i);
                srcCount = Character.charCount(srcChar);
            } else {
                srcCount = 1;
            }
            if (localeDependent) {
                upperChar = ConditionalSpecialCasing.toUpperCaseEx(this, i, locale);
            } else {
                upperChar = Character.toUpperCaseEx(srcChar);
            }
            if ((upperChar == Character.ERROR)
                    || (upperChar >= Character.MIN_SUPPLEMENTARY_CODE_POINT)) {
                if (upperChar == Character.ERROR) {
                    if (localeDependent) {
                        upperCharArray =
                                ConditionalSpecialCasing.toUpperCaseCharArray(this, i, locale);
                    } else {
                        upperCharArray = Character.toUpperCaseCharArray(srcChar);
                    }
                } else if (srcCount == 2) {
                    resultOffset += Character.toChars(upperChar, result, i + resultOffset) - srcCount;
                    continue;
                } else {
                    upperCharArray = Character.toChars(upperChar);
                }

                /* Grow result if needed */
                int mapLen = upperCharArray.length;
                if (mapLen > srcCount) {
                    char[] result2 = new char[result.length + mapLen - srcCount];
                    System.arraycopy(result, 0, result2, 0, i + resultOffset);
                    result = result2;
                }
                for (int x = 0; x < mapLen; ++x) {
                    result[i + resultOffset + x] = upperCharArray[x];
                }
                resultOffset += (mapLen - srcCount);
            } else {
                result[i + resultOffset] = (char)upperChar;
            }
        }
        return new String(result, 0, len + resultOffset);
    }

    /**
     * 直接转换为大写的字符串
     * @return
     */
    public String toUpperCase() {
        return toUpperCase(Locale.getDefault());
    }

    /**
     * 去掉前后空格
     * @return
     */
    public String trim() {
        int len = value.length;
        int st = 0;
        char[] val = value; /* avoid getfield opcode */
        //循环检测第一位致不是' '内容存在 ' '的内容
        while ((st < len) && (val[st] <= ' ')) {
            st++;
        }
        //检测最后一位存在' '的内容
        while ((st < len) && (val[len - 1] <= ' ')) {
            len--;
        }
        //进行处理，以载取方式
        return ((st > 0) || (len < value.length)) ? substring(st, len) : this;
    }

    /** 将内容转成字符串 **/
    public String toString() {
        return this;
    }

    /**
     * 将内容转成字符数组
     * @return
     */
    public char[] toCharArray() {
        // Cannot use Arrays.copyOf because of class initialization order issues
        char result[] = new char[value.length];
        System.arraycopy(value, 0, result, 0, value.length);
        return result;
    }

    /**
     * 格式化内容
     * @param format 格式
     * @param args 参数
     * @return
     */
    public static String format(String format, Object... args) {
        return new Formatter().format(format, args).toString();
    }

    /**
     * 同上 附加了语言
     * @param l
     * @param format
     * @param args
     * @return
     */
    public static String format(Locale l, String format, Object... args) {
        return new Formatter(l).format(format, args).toString();
    }

    /**
     * 将内值转成string 如果为空转输出null
     * @param obj
     * @return
     */
    public static String valueOf(Object obj) {
        return (obj == null) ? "null" : obj.toString();
    }

    /**
     * 将字符数组转成字符串
     * @param data
     * @return
     */
    public static String valueOf(char data[]) {
        return new String(data);
    }

    /**
     * 将字符数组转成字符串
     * @param data 内容
     * @param offset 偏移量
     * @param count 长度
     * @return
     */
    public static String valueOf(char data[], int offset, int count) {
        return new String(data, offset, count);
    }

    /**
     * 复制内容创建字符串
     * @param data
     * @param offset
     * @param count
     * @return
     */
    public static String copyValueOf(char data[], int offset, int count) {
        return new String(data, offset, count);
    }

    /**
     * 通过字符数组进行复制
     * @param data
     * @return
     */
    public static String copyValueOf(char data[]) {
        return new String(data);
    }

    /**
     * 将布尔转成字符串 true 和false
     * @param b
     * @return
     */
    public static String valueOf(boolean b) {
        return b ? "true" : "false";
    }

    /**
     * 将字符转成字符串
     * @param c
     * @return
     */
    public static String valueOf(char c) {
        char data[] = {c};
        return new String(data, true);
    }

    /**
     * 将整弄转成字符串
     * @param i
     * @return
     */
    public static String valueOf(int i) {
        return Integer.toString(i);
    }

    /**
     * 将Long类型转成字符串
     * @param l
     * @return
     */
    public static String valueOf(long l) {
        return Long.toString(l);
    }

    /**
     * 将浮点型转成字符串
     * @param f
     * @return
     */
    public static String valueOf(float f) {
        return Float.toString(f);
    }

    /**
     * 将double转成字符串
     * @param d
     * @return
     */
    public static String valueOf(double d) {
        return Double.toString(d);
    }

    /**
     * 通过字符串池中获取字符串，该对象也会被添加池中 native为本地方法由c++维护看不了源码
     * @return
     */
    public native String intern();
}