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1astore_2 将引用类型或returnAddress类型值存入局部变量2new 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