-
invokeinterface : call interface methods
-
invokespecial method calls the initialize method, private method, or the parent class definition:
-
invokestatic : call the static method
-
invokevirtual : call an instance method
package com.xiaobu.test.StringDemo;
/**
* @author xiaobu
* @version JDK1.8.0_171
* @date on 2019/4/30 16:04
* @description V1.0 走StringBuilder
*/
public class StringDemo3 {
public static void main(String[] args) {
test1();
}
//结果为false
private static void test1() {
String str = "123";
String a = "123";
String str2 = a + "";
System.out.println(str==str2);
}
}
Use idea plug decompile bytecode files
Classfile /E:/Practise/SpringBoot/demo/target/classes/com/xiaobu/test/StringDemo/StringDemo3.class
Last modified 2019-10-22; size 1020 bytes
MD5 checksum fd43b6950ccbd87c2bdd41457f4e50b1
Compiled from "StringDemo3.java"
public class com.xiaobu.test.StringDemo.StringDemo3
minor version: 0
major version: 52 //表明是JDK1.8
flags: ACC_PUBLIC, ACC_SUPER //类的访问标志
Constant pool: //常量池
#1 = Methodref #12.#35 // java/lang/Object."<init>":()V #+数字表示第几个常量 这个指向父类的构造方法
#2 = Methodref #11.#36 // com/xiaobu/test/StringDemo/StringDemo3.test1:()V 指向test1()方法 返回值void
#3 = String #37 // 123
#4 = Class #38 // java/lang/StringBuilder
#5 = Methodref #4.#35 // java/lang/StringBuilder."<init>":()V
#6 = Methodref #4.#39 // java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
#7 = String #40 //
#8 = Methodref #4.#41 // java/lang/StringBuilder.toString:()Ljava/lang/String;
#9 = Fieldref #42.#43 // java/lang/System.out:Ljava/io/PrintStream;
#10 = Methodref #44.#45 // java/io/PrintStream.println:(Z)V
#11 = Class #46 // com/xiaobu/test/StringDemo/StringDemo3
#12 = Class #47 // java/lang/Object
#13 = Utf8 <init>
#14 = Utf8 ()V
#15 = Utf8 Code
#16 = Utf8 LineNumberTable
#17 = Utf8 LocalVariableTable
#18 = Utf8 this
#19 = Utf8 Lcom/xiaobu/test/StringDemo/StringDemo3;
#20 = Utf8 main
#21 = Utf8 ([Ljava/lang/String;)V
#22 = Utf8 args
#23 = Utf8 [Ljava/lang/String;
#24 = Utf8 MethodParameters
#25 = Utf8 test1
#26 = Utf8 str
#27 = Utf8 Ljava/lang/String;
#28 = Utf8 a
#29 = Utf8 str2
#30 = Utf8 StackMapTable
#31 = Class #48 // java/lang/String
#32 = Class #49 // java/io/PrintStream
#33 = Utf8 SourceFile
#34 = Utf8 StringDemo3.java
#35 = NameAndType #13:#14 // "<init>":()V
#36 = NameAndType #25:#14 // test1:()V
#37 = Utf8 123
#38 = Utf8 java/lang/StringBuilder
#39 = NameAndType #50:#51 // append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
#40 = Utf8
#41 = NameAndType #52:#53 // toString:()Ljava/lang/String;
#42 = Class #54 // java/lang/System
#43 = NameAndType #55:#56 // out:Ljava/io/PrintStream;
#44 = Class #49 // java/io/PrintStream
#45 = NameAndType #57:#58 // println:(Z)V
#46 = Utf8 com/xiaobu/test/StringDemo/StringDemo3
#47 = Utf8 java/lang/Object
#48 = Utf8 java/lang/String
#49 = Utf8 java/io/PrintStream
#50 = Utf8 append
#51 = Utf8 (Ljava/lang/String;)Ljava/lang/StringBuilder;
#52 = Utf8 toString
#53 = Utf8 ()Ljava/lang/String;
#54 = Utf8 java/lang/System
#55 = Utf8 out
#56 = Utf8 Ljava/io/PrintStream;
#57 = Utf8 println
#58 = Utf8 (Z)V
{
public com.xiaobu.test.StringDemo.StringDemo3(); //默认构造方法
descriptor: ()V
flags: ACC_PUBLIC
Code: //code表示代码 stack:最大操作数栈 locals:局部变量锁存储的空间:4个字节大小
stack=1, locals=1, args_size=1 // args_size方法参数个数
0: aload_0 //将第一个引用类型本地变量推送至栈顶
1: invokespecial #1 // Method java/lang/Object."<init>":()V
4: return //方法返回
LineNumberTable:
line 9: 0 //第九行源码对应 字节码行号0: aload_0
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this Lcom/xiaobu/test/StringDemo/StringDemo3;
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=0, locals=1, args_size=1
0: invokestatic #2 // Method test1:()V
3: return //方法返回
LineNumberTable:
line 11: 0 //第十一行源码对应 字节码行号0: invokestatic #2
line 12: 3 //第十二行源码对应 字节码行号3: return
LocalVariableTable:
Start Length Slot Name Signature
0 4 0 args [Ljava/lang/String;
MethodParameters:
Name Flags
args
}
SourceFile: "StringDemo3.java"
As can be seen above, the code underlying StringBuilder away, splicing string, and then calls the StringBuilder toString method.
package com.xiaobu.test.StringDemo;
/**
* @author xiaobu
* @version JDK1.8.0_171
* @date on 2019/4/30 16:04
* @description V1.0 走String
*/
public class StringDemo4 {
public static void main(String[] args) {
test1();
}
//结果为true
private static void test1() {
String str = "11";
String a = "11";
String str2 = "11" + "";
System.out.println(str==str2);
}
}
Decompile bytecode files
Classfile /E:/Practise/SpringBoot/demo/target/classes/com/xiaobu/test/StringDemo/StringDemo4.class
Last modified 2019-10-22; size 851 bytes
MD5 checksum 045bcada94c8d6c922754d92f6242259
Compiled from "StringDemo4.java"
public class com.xiaobu.test.StringDemo.StringDemo4
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #7.#30 // java/lang/Object."<init>":()V
#2 = Methodref #6.#31 // com/xiaobu/test/StringDemo/StringDemo4.test1:()V
#3 = String #32 // 11
#4 = Fieldref #33.#34 // java/lang/System.out:Ljava/io/PrintStream;
#5 = Methodref #35.#36 // java/io/PrintStream.println:(Z)V
#6 = Class #37 // com/xiaobu/test/StringDemo/StringDemo4
#7 = Class #38 // java/lang/Object
#8 = Utf8 <init>
#9 = Utf8 ()V
#10 = Utf8 Code
#11 = Utf8 LineNumberTable
#12 = Utf8 LocalVariableTable
#13 = Utf8 this
#14 = Utf8 Lcom/xiaobu/test/StringDemo/StringDemo4;
#15 = Utf8 main
#16 = Utf8 ([Ljava/lang/String;)V
#17 = Utf8 args
#18 = Utf8 [Ljava/lang/String;
#19 = Utf8 MethodParameters
#20 = Utf8 test1
#21 = Utf8 str
#22 = Utf8 Ljava/lang/String;
#23 = Utf8 a
#24 = Utf8 str2
#25 = Utf8 StackMapTable
#26 = Class #39 // java/lang/String
#27 = Class #40 // java/io/PrintStream
#28 = Utf8 SourceFile
#29 = Utf8 StringDemo4.java
#30 = NameAndType #8:#9 // "<init>":()V
#31 = NameAndType #20:#9 // test1:()V
#32 = Utf8 11
#33 = Class #41 // java/lang/System
#34 = NameAndType #42:#43 // out:Ljava/io/PrintStream;
#35 = Class #40 // java/io/PrintStream
#36 = NameAndType #44:#45 // println:(Z)V
#37 = Utf8 com/xiaobu/test/StringDemo/StringDemo4
#38 = Utf8 java/lang/Object
#39 = Utf8 java/lang/String
#40 = Utf8 java/io/PrintStream
#41 = Utf8 java/lang/System
#42 = Utf8 out
#43 = Utf8 Ljava/io/PrintStream;
#44 = Utf8 println
#45 = Utf8 (Z)V
{
public com.xiaobu.test.StringDemo.StringDemo4();
descriptor: ()V
flags: ACC_PUBLIC
Code:
stack=1, locals=1, args_size=1
0: aload_0
1: invokespecial #1 // Method java/lang/Object."<init>":()V
4: return
LineNumberTable:
line 9: 0
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this Lcom/xiaobu/test/StringDemo/StringDemo4;
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=0, locals=1, args_size=1
0: invokestatic #2 // Method test1:()V
3: return
LineNumberTable:
line 11: 0
line 12: 3
LocalVariableTable:
Start Length Slot Name Signature
0 4 0 args [Ljava/lang/String;
MethodParameters:
Name Flags
args
}
SourceFile: "StringDemo4.java"
Go directly above the strings together.
Reference:
Easy to read bytecode
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