Java 多线程系列(1) —— 线程入门

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发布于 2020-11-25 15:14:39

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Java 中线程的基础知识

线程的属性

ID: 线程的ID，由系统自动分配
Priority: 线程的优先级，若果不设置，将会和调用他的父线程等级相同
Name: 线程的名称，由系统自动创建，格式为“ Thread + 线程初始化数字”
Status: 线程的状态，初始化为 0，代表 new 状态上述属性在源码中的定义为：

线程优先级

Java 中线程的优先级范围为 1~10，是一个 int 类型的值其中最小的优先级 (MIN_PRIORITY) 为 1 正常优先级 (NORM_PRIORITY) 为 5 最高优先级 (MAX_PRIORITY) 为 10 【源码中定义的线程优先级】

线程的状态

Java 中的线程有 6 中状态

NEW：线程创建完毕，但是并未开始执行
RUNABLE：线程正在 JVM 中运行
BLOCKED：线程处于阻塞状态，并且等待另一个线程
WAITING：线程正在等待另一个线程
TIMED_WAITING：线程等待另一个线程一段时间
TERMINATED：线程执行完毕

线程的状态在源码中定义为枚举类型

    public enum State {
        /**
         * Thread state for a thread which has not yet started.
         */
        NEW,

        /**
         * Thread state for a runnable thread.  A thread in the runnable
         * state is executing in the Java virtual machine but it may
         * be waiting for other resources from the operating system
         * such as processor.
         */
        RUNNABLE,

        /**
         * Thread state for a thread blocked waiting for a monitor lock.
         * A thread in the blocked state is waiting for a monitor lock
         * to enter a synchronized block/method or
         * reenter a synchronized block/method after calling
         * {@link Object#wait() Object.wait}.
         */
        BLOCKED,

        /**
         * Thread state for a waiting thread.
         * A thread is in the waiting state due to calling one of the
         * following methods:
         * <ul>
         *   <li>{@link Object#wait() Object.wait} with no timeout</li>
         *   <li>{@link #join() Thread.join} with no timeout</li>
         *   <li>{@link LockSupport#park() LockSupport.park}</li>
         * </ul>
         *
         * <p>A thread in the waiting state is waiting for another thread to
         * perform a particular action.
         *
         * For example, a thread that has called <tt>Object.wait()</tt>
         * on an object is waiting for another thread to call
         * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
         * that object. A thread that has called <tt>Thread.join()</tt>
         * is waiting for a specified thread to terminate.
         */
        WAITING,

        /**
         * Thread state for a waiting thread with a specified waiting time.
         * A thread is in the timed waiting state due to calling one of
         * the following methods with a specified positive waiting time:
         * <ul>
         *   <li>{@link #sleep Thread.sleep}</li>
         *   <li>{@link Object#wait(long) Object.wait} with timeout</li>
         *   <li>{@link #join(long) Thread.join} with timeout</li>
         *   <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
         *   <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
         * </ul>
         */
        TIMED_WAITING,

        /**
         * Thread state for a terminated thread.
         * The thread has completed execution.
         */
        TERMINATED;
    }

线程的创建方式

Java 中创建线程的三种方式：

继承 Thread 类
实现 Runnable 接口
实现 Callable 接口（并发）

继承 Thread 类方式创建线程

package com.stu.edu.demo1;

public class ThreadDemo1 extends Thread {
	
	public static void main(String[] args) {
		ThreadDemo1 thread1 = new ThreadDemo1();
		ThreadDemo1 thread2 = new ThreadDemo1();
		thread1.setName("THREAD_ONE");
		thread2.setName("THREAD_TWO");
		thread1.start();
		thread2.start();
	}
	
	@Override
	public void run() {
		for(int i = 0; i < 1000; i++) {
			System.out.println(Thread.currentThread().getName() + " ---------> " + i);
		}
	}
}

实现 Runable 接口方式创建线程

package com.stu.edu.demo1;

public class ThreadDemo1 implements Runnable {
	
	public static void main(String[] args) {
		ThreadDemo1 run1 = new ThreadDemo1();
		ThreadDemo1 run2 = new ThreadDemo1();
		Thread thread1 = new Thread(run1,"THREAD_ONE");
		Thread thread2 = new Thread(run2,"THREAD_TWO");
		thread1.start();
		thread2.start();
	}
	
	@Override
	public void run() {
		for(int i = 0; i < 1000; i++) {
			System.out.println(Thread.currentThread().getName() + " ---------> " + i);
		}
	}
}

在创建线程时调用

实现 Callable 接口方式创建线程

package com.stu.edu.demo1;

import java.util.concurrent.Callable;
import java.util.concurrent.FutureTask;

public class ThreadDemo1 implements Callable {
	
	public static void main(String[] args) {
		ThreadDemo1 call1 = new ThreadDemo1();
		ThreadDemo1 call2 = new ThreadDemo1();
		FutureTask<Object> thread1 = new FutureTask<>(call1);
		FutureTask<Object> thread2 = new FutureTask<>(call2);
		new Thread(thread1,"THREAD_ONE").start();
		new Thread(thread2,"THREAD_TWO").start();
	}
	

	@Override
	public Object call() throws Exception {
		for(int i = 0; i < 1000; i++) {
			System.out.println(Thread.currentThread().getName() + " ---------> " + i);
		}
		return null;
	}
}

【call接口代码图片】