java 获取内存中的对象 java获取对象在内存的大小

Java基本类型长度及对应对象的字节长度
基本类型 长度 the size of an object
Int 　　　  4 　　 16
Short 　　 2 　　 16
Long 　　 8 　　  24
Byte 　　  1 　　  16
Character 1 　　  16
Float 　　 4 　　  16
Double 　 8 　　  24

在JDK1.8中可以采用ObjectSizeCalculator类来计算对象在内存中的大小

import java.sql.Timestamp;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;

import jdk.nashorn.internal.ir.debug.ObjectSizeCalculator;

public class Test {

    public static void main(String[] args) {

        System.out.println("Integer: " + ObjectSizeCalculator.getObjectSize(Integer.valueOf(122)));
        System.out.println("Long: " + ObjectSizeCalculator.getObjectSize(Long.valueOf(122L)));
        System.out.println("Double: " + ObjectSizeCalculator.getObjectSize(Double.valueOf(122.22)));
        System.out.println("Float: " + ObjectSizeCalculator.getObjectSize(Float.valueOf(122.22f)));
        System.out.println("Boolean: " + ObjectSizeCalculator.getObjectSize(Boolean.valueOf(false)));
        System.out.println("Character: " + ObjectSizeCalculator.getObjectSize(Character.valueOf('a')));
        System.out.println("Short: " + ObjectSizeCalculator.getObjectSize(Short.valueOf("1")));
        System.out.println("Byte: " + ObjectSizeCalculator.getObjectSize(Byte.valueOf("1")));
        System.out.println("Date: " + ObjectSizeCalculator.getObjectSize(new Date()));
        System.out.println("Timestamp: " + ObjectSizeCalculator.getObjectSize(new Timestamp(System.currentTimeMillis())));

        Map<String, Object> map = new HashMap<>();
        map.put("11", 11);
        map.put("22", "22");
        map.put("33", 33L);
        map.put("44", 44.44);

        System.out.println("Map: " + ObjectSizeCalculator.getObjectSize(map));

    }

}

运行结果：

Integer: 16
Long: 24
Double: 24
Float: 16
Boolean: 16
Character: 16
Short: 16
Byte: 16
Date: 24
Timestamp: 32
Map: 512