在java中 你知道String对"+"做了什么吗

相关学习推荐：java基础教程

下面有段简单的代码

public class StringPlusTest{     public static void main(String[] args) {         String s1 = "aaa";         String s2 = "bbb";         String s = "ccc" +s1 + s2 +"ddd";     }}

使用 javap -c .StringPlusTest.class反编译一下，得到

Compiled from "StringPlusTest.java"public class com.epoint.codetuning.test.StringPlusTest {   public com.epoint.codetuning.test.StringPlusTest();     Code:        0: aload_0       1: invokespecial #1                  // Method java/lang/Object."<init>":()V        4: return    public static void main(java.lang.String[]);     Code:        0: ldc           #2                  // String aaa        2: astore_1       3: ldc           #3                  // String bbb        5: astore_2       6: new           #4                  // class java/lang/StringBuilder        9: dup      10: invokespecial #5                  // Method java/lang/StringBuilder."<init>":()V       13: ldc           #6                  // String ccc       15: invokevirtual #7                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;       18: aload_1      19: invokevirtual #7                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;       22: aload_2      23: invokevirtual #7                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;       26: ldc           #8                  // String ddd       28: invokevirtual #7                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;       31: invokevirtual #9                  // Method java/lang/StringBuilder.toString:()Ljava/lang/String;       34: astore_3      35: return}

其中，

ldc 把常量池中的项压入栈 astore_1 将引用类型或returnAddress类型值存入局部变量1 astore_2 将引用类型或returnAddress类型值存入局部变量2 new 创建一个新对象 dup 复制栈顶部一个字长内容 invokespecial 根据编译时类型来调用实例方法 aload_1 从局部变量1中装载引用类型值 aload_2 从局部变量2中装载引用类型值 astore_3 将引用类型或returnAddress类型值存入局部变量3