简单说说<init>和<clinit>
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2022-03-05 15:42:24
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<clinit>:在初始化时执行,从上到下的收集有初始值的静态成员域或static块的值,进行赋值,执行本类的<clinit>函数时,父类的<clinit>函数已经执行完毕,若本类不具有静态成员域或static块,则JVM不会为该类产生<clinit>函数。
<init>:其实就是构造函数,在生成class文件时,编译器会在构造函数中添加一些代码,在本类的构造函数中,会最优先调用父类的<init>函数,接着执行剩余构造函数中剩余的代码,我们来看看下面的代码:
class deal0
{
}
class deal extends deal0
{
int n;
int m=2;
deal()
{
n=1;
}
}
public class Try {
public static void main(String[] args) {
deal x=new deal();
}
}
反编译deal.class文件:
Last modified 2018-1-31; size 240 bytes
MD5 checksum 8b1b2a8d7345905b383f50f5fd6d2a2a
Compiled from "Try.java"
class deal extends deal0
minor version: 0
major version: 52
flags: ACC_SUPER
Constant pool:
#1 = Methodref #5.#15 // deal0."<init>":()V
#2 = Fieldref #4.#16 // deal.m:I
#3 = Fieldref #4.#17 // deal.n:I
#4 = Class #18 // deal
#5 = Class #19 // deal0
#6 = Utf8 n
#7 = Utf8 I
#8 = Utf8 m
#9 = Utf8 <init>
#10 = Utf8 ()V
#11 = Utf8 Code
#12 = Utf8 LineNumberTable
#13 = Utf8 SourceFile
#14 = Utf8 Try.java
#15 = NameAndType #9:#10 // "<init>":()V
#16 = NameAndType #8:#7 // m:I
#17 = NameAndType #6:#7 // n:I
#18 = Utf8 deal
#19 = Utf8 deal0
{
int n;
descriptor: I
flags:
int m;
descriptor: I
flags:
deal();
descriptor: ()V
flags:
Code:
stack=2, locals=1, args_size=1
0: aload_0 //将this指针压入操作数栈
1: invokespecial #1 //Method deal0."<init>":()V,此处调用父类的构造函数,父类构造函数的执行结果写入到this指针所指的内存处
4: aload_0 //将this指针压入操作数栈
5: iconst_2 //将常量池中2压入操作数栈
6: putfield #2 // Field m:I,使内存中m的值为2,此时会用到操作数栈中的this指针,来找到实例对象在堆内存中的位置。
9: aload_0 //将this指针压入操作数栈
10: iconst_1 //将常量池中的1压入操作数栈,this指针作用同上
11: putfield #3 // Field n:I,给内存中的n赋予1
14: return
LineNumberTable:
line 10: 0
line 8: 4
line 11: 9
line 12: 14
}
SourceFile: "Try.java"
构造函数的字节码解释请看注释,可以看到<init>先调用父类的<init>函数,接着初始化具有初始值的变量(实测后,初始化顺序为代码中由上到下的出现顺序),然后在执行我们自己写的代码。 上一篇: Java学习笔记——网络编程
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