Getting Object Size


    Since JDK 1.5 Java have a new feature to get size of the Object.

  • In many cases you want to optimize the object size.
  • Java has Instrumentation interface to get the object size.
  • Instrumentation interface has the concept of premain().
  • Header of the program consume 8 bytes.
  • Object size must be calculate in multiply of 8.
    • Steps to get Object size:
    • Step 1 : First make a program in java
      • import java.lang.instrument.Instrumentation;

class B
{
	/* Header Info 8 Byte */
	int x; //4
	float y;  // 4
	long d; //8
	String z; //4
}

class C
{	
}

public class A
{
	/* new concept */
	public static void premain(String args, Instrumentation ins)
	{
		B obj = new B();
		long size = ins.getObjectSize(obj);
		System.out.println("B Size is "+size);
		size = ins.getObjectSize(new C());
		System.out.println("C size is "+size);
		String q ="test";
		size = ins.getObjectSize(q);
		System.out.println("Q String size is "+size);
	}
	public static void main(String[] args)
	{
		System.out.println("Inside Main ");
	}
}
    • Step 2 : make the Executable JAR file of that project
    • Step 3 : put the premain() entry in manifest file.
    • Step 4 : Execute the JAR.