java 之方法调用 方法传参 值传递还是引用传递字节码
?package com.zhang;public class Test{ public static void changeStr(String str){ str="welcome"; } public static void main(String[] args) { String str="1234"; changeStr(str); System.out.println(str); }}/* * Compiled from "Test.java"public class Test extends java.lang.Object SourceFile: "Test.java" minor version: 0 major version: 50 Constant pool:const #1 = Method #8.#19; // java/lang/Object."<init>":()Vconst #2 = String #20; // welcomeconst #3 = String #21; // 1234const #4 = Method #7.#22; // Test.changeStr:(Ljava/lang/String;)Vconst #5 = Field #23.#24; // java/lang/System.out:Ljava/io/PrintStream;const #6 = Method #25.#26; // java/io/PrintStream.println:(Ljava/lang/String;)Vconst #7 = class #27; // Testconst #8 = class #28; // java/lang/Objectconst #9 = Asciz <init>;const #10 = Asciz ()V;const #11 = Asciz Code;const #12 = Asciz LineNumberTable;const #13 = Asciz changeStr;const #14 = Asciz (Ljava/lang/String;)V;const #15 = Asciz main;const #16 = Asciz ([Ljava/lang/String;)V;const #17 = Asciz SourceFile;const #18 = Asciz Test.java;const #19 = NameAndType #9:#10;// "<init>":()Vconst #20 = Asciz welcome;const #21 = Asciz 1234;const #22 = NameAndType #13:#14;// changeStr:(Ljava/lang/String;)Vconst #23 = class #29; // java/lang/Systemconst #24 = NameAndType #30:#31;// out:Ljava/io/PrintStream;const #25 = class #32; // java/io/PrintStreamconst #26 = NameAndType #33:#14;// println:(Ljava/lang/String;)Vconst #27 = Asciz Test;const #28 = Asciz java/lang/Object;const #29 = Asciz java/lang/System;const #30 = Asciz out;const #31 = Asciz Ljava/io/PrintStream;;const #32 = Asciz java/io/PrintStream;const #33 = Asciz println;{public Test(); Code: Stack=1, Locals=1, Args_size=1 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return LineNumberTable: line 1: 0public static void changeStr(java.lang.String); Code: Stack=1, Locals=1, Args_size=1 0: ldc #2; //String welcome 将string welcome常量从常量池取出，推入栈顶 2: astore_0 //将栈顶引用类型数值存到第一个本地变量（局部变量表） 3: return LineNumberTable: line 3: 0 line 4: 3public static void main(java.lang.String[]); Code: Stack=2, Locals=2, Args_size=1 0: ldc #3; //String 1234 将string 1234常量从常量池取出，推入栈顶 2: astore_1 //将栈顶引用类型数值存到第二个本地变量（局部变量表） 3: aload_1 //将第二个引用类型本地变量推送至栈顶 4: invokestatic #4; //Method changeStr:(Ljava/lang/String;)V 7: getstatic #5; //Field java/lang/System.out:Ljava/io/PrintStream; 10: aload_1 //将第二个引用类型本地变量推送至栈顶 11: invokevirtual #6; //Method java/io/PrintStream.println:(Ljava/lang/String;)V 14: return LineNumberTable: line 6: 0 line 7: 3 line 8: 7 line 9: 14} * */ ?
package com.zhang;public class Test4{ public static void changeStr(T str){ str.name = "sf"; } public static void main(String[] args) { T t = new T(); changeStr(t); System.out.println(t.name); }}class T{String name = "name--min";@Overridepublic String toString() {// TODO Auto-generated method stubreturn name;}}/* *Compiled from "Test4.java"public class Test4 extends java.lang.Object SourceFile: "Test4.java" minor version: 0 major version: 50 Constant pool:const #1 = Method #10.#21; // java/lang/Object."<init>":()Vconst #2 = String #22; // sfconst #3 = Field #4.#23; // T.name:Ljava/lang/String;const #4 = class #24; // Tconst #5 = Method #4.#21; // T."<init>":()Vconst #6 = Method #9.#25; // Test4.changeStr:(LT;)Vconst #7 = Field #26.#27; // java/lang/System.out:Ljava/io/Printtream;const #8 = Method #28.#29; // java/io/PrintStream.println:(Ljava/ang/String;)Vconst #9 = class #30; // Test4const #10 = class #31; // java/lang/Objectconst #11 = Asciz <init>;const #12 = Asciz ()V;const #13 = Asciz Code;const #14 = Asciz LineNumberTable;const #15 = Asciz changeStr;const #16 = Asciz (LT;)V;const #17 = Asciz main;const #18 = Asciz ([Ljava/lang/String;)V;const #19 = Asciz SourceFile;const #20 = Asciz Test4.java;const #21 = NameAndType #11:#12;// "<init>":()Vconst #22 = Asciz sf;const #23 = NameAndType #32:#33;// name:Ljava/lang/String;const #24 = Asciz T;const #25 = NameAndType #15:#16;// changeStr:(LT;)Vconst #26 = class #34; // java/lang/Systemconst #27 = NameAndType #35:#36;// out:Ljava/io/PrintStream;const #28 = class #37; // java/io/PrintStreamconst #29 = NameAndType #38:#39;// println:(Ljava/lang/String;)Vconst #30 = Asciz Test4;const #31 = Asciz java/lang/Object;const #32 = Asciz name;const #33 = Asciz Ljava/lang/String;;const #34 = Asciz java/lang/System;const #35 = Asciz out;const #36 = Asciz Ljava/io/PrintStream;;const #37 = Asciz java/io/PrintStream;const #38 = Asciz println;const #39 = Asciz (Ljava/lang/String;)V;{public Test4(); Code: Stack=1, Locals=1, Args_size=1 0: aload_0 1: invokespecial #1; //Method java/lang/Object."<init>":()V 4: return LineNumberTable: line 1: 0public static void changeStr(T); Code: Stack=2, Locals=1, Args_size=1 0: aload_0 ////将栈顶引用类型数值存到第一个本地变量（局部变量表） 1: ldc #2; //String sf 将string sf常量从常量池取出，推入栈顶 3: putfield #3; //Field T.name:Ljava/lang/String;//为t对象的name字段赋值 6: return LineNumberTable: line 3: 0 line 4: 6public static void main(java.lang.String[]); Code: Stack=2, Locals=2, Args_size=1 0: new #4; //class T 创建一个新对象，并压入栈顶 3: dup //复制栈顶数值，并将复制值压入栈顶 4: invokespecial #5; //Method T."<init>":()V 调入无参够造方法 7: astore_1 //将栈顶引用类型数值存到第二个本地变量（局部变量表） 8: aload_1 //将第二个引用类型本地变量推送至栈顶 9: invokestatic #6; //Method changeStr:(LT;)V 12: getstatic #7; //Field java/lang/System.out:Ljava/io/PrintStream; 15: aload_1 //将第二个引用类型本地变量推送至栈顶 16: getfield #3; //Field T.name:Ljava/lang/String; //获取对象的相应字段name。并压入栈顶 19: invokevirtual #8; //Method java/io/PrintStream.println:(Ljava/lang/Sting;)V 22: return LineNumberTable: line 7: 0 line 8: 8 line 9: 12 line 10: 22} * */ ?