java 打印当前内存 java打印内存信息

1、maven 依赖

<dependency>
	<groupId>org.openjdk.jol</groupId>
	<artifactId>jol-core</artifactId>
	<version>0.10</version>
</dependency>

 

2、测试类

package constxiong;

import org.openjdk.jol.info.ClassLayout;
import org.openjdk.jol.info.GraphLayout;

/**
 * 测试对象占用的内存信息
 */
public class TestObjectSize {

    public static void main(String[] args) {
        System.out.println("对象内部信息");
        System.out.println(ClassLayout.parseInstance(new String("ConstXiong")).toPrintable());
        System.out.println(ClassLayout.parseInstance(new char[]{'C', 'o', 'n', 's', 't', 'X', 'i', 'o', 'n', 'g'}).toPrintable());

        System.out.println("对象整体信息");
        System.out.println(GraphLayout.parseInstance(new String("ConstXiong")).toPrintable());
        System.out.println(GraphLayout.parseInstance(new char[]{'C', 'o', 'n', 's', 't', 'X', 'i', 'o', 'n', 'g'}).toPrintable());

        System.out.println("对象占用总空间");
        System.out.println(GraphLayout.parseInstance(new String("ConstXiong")).totalSize());
        System.out.println(GraphLayout.parseInstance(new char[]{'C', 'o', 'n', 's', 't', 'X', 'i', 'o', 'n', 'g'}).totalSize());
    }
}

 

3、打印结果

对象内部信息
java.lang.String object internals:
 OFFSET  SIZE     TYPE DESCRIPTION                               VALUE
      0     4          (object header)                           01 00 00 00 (00000001 00000000 00000000 00000000) (1)
      4     4          (object header)                           00 00 00 00 (00000000 00000000 00000000 00000000) (0)
      8     4          (object header)                           d0 16 3e 17 (11010000 00010110 00111110 00010111) (389945040)
     12     4   char[] String.value                              [C, o, n, s, t, X, i, o, n, g]
     16     4      int String.hash                               0
     20     4          (loss due to the next object alignment)
Instance size: 24 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total

[C object internals:
 OFFSET  SIZE   TYPE DESCRIPTION                               VALUE
      0     4        (object header)                           01 00 00 00 (00000001 00000000 00000000 00000000) (1)
      4     4        (object header)                           00 00 00 00 (00000000 00000000 00000000 00000000) (0)
      8     4        (object header)                           08 02 3e 17 (00001000 00000010 00111110 00010111) (389939720)
     12     4        (object header)                           0a 00 00 00 (00001010 00000000 00000000 00000000) (10)
     16    20   char [C.<elements>                             N/A
     36     4        (loss due to the next object alignment)
Instance size: 40 bytes
Space losses: 0 bytes internal + 4 bytes external = 4 bytes total


对象整体信息
java.lang.String@1a93a7cad object externals:
          ADDRESS       SIZE TYPE             PATH                           VALUE
         d6284f40         40 [C               .value                         [C, o, n, s, t, X, i, o, n, g]
         d6284f68   11751072 (something else) (somewhere else)               (something else)
         d6db9e08         24 java.lang.String                                (object)


[C@3b764bced object externals:
          ADDRESS       SIZE TYPE PATH                           VALUE
         d6df9610         40 [C                                  [C, o, n, s, t, X, i, o, n, g]



对象占用总空间
64
40

 

内存分析：

https://www.javanav.com/val/49e9ce5857744a39a88b1977d84086c7.html