Java中的+会利用StringBuilder来实现，例如



public class Test1 {


/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
        StringBuilder sb = new StringBuilder("0123456789");
        StringBuilder sb1 = new StringBuilder();
        for(int i = 0; i < 100; i++){
        sb1.append("1");
        }
        System.out.println("length " + sb.length() + " Capacity " + sb.capacity());
        //String str = null;
        sb.append(sb1.toString());
        System.out.println(sb.capacity() + " " +sb.toString());
}


}

用jad反编译为
// Decompiled by Jad v1.5.8g. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://www.kpdus.com/jad.html
// Decompiler options: packimports(3) 
// Source File Name:   Test1.java


import java.io.PrintStream;


public class Test1
{


    public Test1()
    {
    }


    public static void main(String args[])
    {
        StringBuilder sb = new StringBuilder("0123456789");
        StringBuilder sb1 = new StringBuilder();
        for(int i = 0; i < 100; i++)
            sb1.append("1");


        System.out.println((new StringBuilder("length ")).append(sb.length()).append(" Capacity ").append(sb.capacity()).toString());
        sb.append(sb1.toString());
        System.out.println((new StringBuilder(String.valueOf(sb.capacity()))).append(" ").append(sb.toString()).toString());
    }
}