浅显易懂的JAVA对象布局

天下文章一大抄！！！！

现在由于资源的共享，很多技术平台的文章都很丰富，但是丰富中夹杂着多数的雷同，并且也没有什么依据，可能仅仅是自己的见解和别人的见解，没有真正的回归本质真理的实践。

 

那么想要最浅显的弄清楚JAVA的对象布局，其实很简单：

1.创建一个Maven项目

2.引入jol的jar包

        <dependency>
            <groupId>org.openjdk.jol</groupId>
            <artifactId>jol-core</artifactId>
            <version>0.9</version>
        </dependency>

3.创建实体类

package com.zking.lock;

/**
 * @description:
 * @author: codinglife
 * @time: 2021/3/22 16:29
 */
public class SynPojo {
    private String s;

    private boolean b;

    private boolean c;

    private int i;

    private float f;

    private byte by;

    private double d;

    private String name;

    private Integer id;

    private Byte aByte;

    private Double aDouble;

    private Float aFloat;

    private SynPojos synPojos;

    public float getF() {
        return f;
    }

    public void setF(float f) {
        this.f = f;
    }

    public byte getBy() {
        return by;
    }

    public void setBy(byte by) {
        this.by = by;
    }

    public double getD() {
        return d;
    }

    public void setD(double d) {
        this.d = d;
    }

    public String getS() {
        return s;
    }

    public void setS(String s) {
        this.s = s;
    }

    public boolean isB() {
        return b;
    }

    public void setB(boolean b) {
        this.b = b;
    }

    public boolean isC() {
        return c;
    }

    public void setC(boolean c) {
        this.c = c;
    }

    public int getI() {
        return i;
    }

    public void setI(int i) {
        this.i = i;
    }

    public Float getaFloat() {
        return aFloat;
    }

    public void setaFloat(Float aFloat) {
        this.aFloat = aFloat;
    }

    public SynPojos getSynPojos() {
        return synPojos;
    }

    public void setSynPojos(SynPojos synPojos) {
        this.synPojos = synPojos;
    }

    public Double getaDouble() {
        return aDouble;
    }

    public void setaDouble(Double aDouble) {
        this.aDouble = aDouble;
    }

    public Byte getaByte() {
        return aByte;
    }

    public void setaByte(Byte aByte) {
        this.aByte = aByte;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

package com.zking.lock;

/**
 * @description:
 * @author: codinglife
 * @time: 2021/3/22 16:29
 */
public class SynPojos {
    private String name;

    private Integer id;

    private Byte aByte;

    private Double aDouble;

    public Double getaDouble() {
        return aDouble;
    }

    public void setaDouble(Double aDouble) {
        this.aDouble = aDouble;
    }

    public Byte getaByte() {
        return aByte;
    }

    public void setaByte(Byte aByte) {
        this.aByte = aByte;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

3.运行

package com.zking.lock;

import org.openjdk.jol.info.ClassLayout;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

/**
 * @description:
 * @author: codinglife
 * @time: 2021/3/22 16:24
 */
public class Syn {


    public static void main(String[] args) {

        synchronized (Syn.class){

            System.out.println(ClassLayout.parseClass(SynPojo.class).toPrintable());



        }



    }




}

4.结果

如图可见，

对象头为12Btye

实例数据根据数据类型来判断：

8大数据类型：

每种基础类型封装类型或其他实例对象各占4Byte，这里占51个byte

对齐数据为8的倍数，这里补1个byte

 

java对象布局：

1.对象头 (mark word+class Metadata Address)(12Byte) 固定大小

2.实例数据 （每种封装类型或对象4Byte，8大基础类型各有大小） 和数据类型有关

3.对齐 (满足8的倍数) 对象大小为8的倍数 向上补齐