分离字符串中的字母和数字并使得字母在前数组在后

public class 校招 {

    static String stringCharFrontNumEnd(String string){
        if(string==null ||string.length()==0)
            return null;
        String charString="";
        String numString="";
        for(int i=0;i<string.length();i++){
            if(string.charAt(i)>='0'  && string.charAt(i)<='9')
            	System.out.println(string.charAt(i));
                numString=numString + string.charAt(i);
            if(string.charAt(i)>='a' && string.charAt(i)<='z' || string.charAt(i)>='A' && string.charAt(i)<='Z')
                charString= charString + string.charAt(i);
        }
        return charString+numString;
    }
    public static void main(String[] args) {
        String string="h3a2p0p1y";
        System.out.println(string + " --> " + stringCharFrontNumEnd(string));
    }

}