对象的实例化内存布局与访问定位
# JVM-对象的实例化内存布局与访问定位
面试题
对象在JVM中是怎么存储的?
对象头信息里面有哪些东西?
Java对象头里有什么?
# 1. 对象实例化
# 1. 对象的实例化 (opens new window)
# 2. 对象的创建字节码角度
- 源码
public class ObjectTest {
public static void main(String[] args) {
Object o = new Object();
}
}
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- 执行命令
java -v -p ObjectTest.class
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- 结果
D:\java-code\java\jvm\target\classes\com\chggx\jvm\chapter10>javap -v -p ObjectTest.class
Classfile /D:/java-code/java/jvm/target/classes/com/chggx/jvm/chapter10/ObjectTest.class
Last modified 2020-12-27; size 468 bytes
MD5 checksum 2a4d696213cdd30c4a65ce13dcab2338
Compiled from "ObjectTest.java"
public class com.chggx.jvm.chapter10.ObjectTest
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #2.#19 // java/lang/Object."<init>":()V
#2 = Class #20 // java/lang/Object
#3 = Class #21 // com/chggx/jvm/chapter10/ObjectTest
#4 = Utf8 <init>
#5 = Utf8 ()V
#6 = Utf8 Code
#7 = Utf8 LineNumberTable
#8 = Utf8 LocalVariableTable
#9 = Utf8 this
#10 = Utf8 Lcom/chggx/jvm/chapter10/ObjectTest;
#11 = Utf8 main
#12 = Utf8 ([Ljava/lang/String;)V
#13 = Utf8 args
#14 = Utf8 [Ljava/lang/String;
#15 = Utf8 o
#16 = Utf8 Ljava/lang/Object;
#17 = Utf8 SourceFile
#18 = Utf8 ObjectTest.java
#19 = NameAndType #4:#5 // "<init>":()V
#20 = Utf8 java/lang/Object
#21 = Utf8 com/chggx/jvm/chapter10/ObjectTest
{
public com.chggx.jvm.chapter10.ObjectTest();
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 8: 0
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this Lcom/chggx/jvm/chapter10/ObjectTest;
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=2, locals=2, args_size=1
// 创建对象的步骤
0: new #2 // class java/lang/Object
3: dup
4: invokespecial #1 // Method java/lang/Object."<init>":()V
7: astore_1
8: return
LineNumberTable:
line 11: 0
line 12: 8
LocalVariableTable:
Start Length Slot Name Signature
0 9 0 args [Ljava/lang/String;
8 1 1 o Ljava/lang/Object;
}
SourceFile: "ObjectTest.java"
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# 2. 对象的内存布局
# 1. 内存布局 (opens new window)
# 2. 图示 (opens new window)
# 3. 对象的访问定位
# 1. JVM是如何通过栈帧中的对象引用访问到其内部的对象实例的呢?
句柄访问图示
直接指针图示
上次更新: 2023/03/27, 08:56:25