一、直接上手

• maven 依赖：

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

• 函数使用：

  import org.openjdk.jol.info.ClassLayout;
  
  public class LayoutDemo {
  	public static void main(String[] args) {
      	MyTest myTest = new MyTest();
      	System.out.println("myTest:"+myTest);
      	System.out.println(ClassLayout.parseInstance(myTest).toPrintable());
  	}
  }
  

• 输出内容：

  myTest:MyTest(a=0, b=false)
  # WARNING: Unable to attach Serviceability Agent. You can try again with escalated privileges. Two options: a) use -Djol.tryWithSudo=true to try with sudo; b) echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope
  com.pilaf.classlayout.MyTest 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)                           43 c1 00 f8 (01000011 11000001 00000000 11111000) (-134168253)
   12     4       int MyTest.a                                  0
   16     1   boolean MyTest.b                                  false
   17     7           (loss due to the next object alignment)
  Instance size: 24 bytes
  Space losses: 0 bytes internal + 7 bytes external = 7 bytes total
  

二、详细分析

https://blog.csdn.net/weixin_40865973/article/details/105390202