How to Determine the Size of Objects in Java?

Finding the Size of Objects in Java

In Java, the question of determining the memory footprint of an object arises frequently when comparing data structures. However, unlike C/C with its sizeOf() method, Java lacks an explicit method for this purpose.

Solution: Utilizing java.lang.instrumentation

The lack of a built-in method in Java necessitates an alternative approach. One suitable solution is to leverage the java.lang.instrumentation package. This package provides a method that delivers an implementation-specific approximation of an object's size, along with any associated overhead.

Code Example:

The following code snippet demonstrates the usage of the java.lang.instrumentation package to retrieve object sizes:

<code class="java">import java.lang.instrument.Instrumentation;

public class ObjectSizeFetcher {
    private static Instrumentation instrumentation;

    public static void premain(String args, Instrumentation inst) {
        instrumentation = inst;
    }

    public static long getObjectSize(Object o) {
        return instrumentation.getObjectSize(o);
    }
}</code>

To determine the size of an object, simply use the getObjectSize method:

<code class="java">public class C {
    private int x;
    private int y;

    public static void main(String [] args) {
        System.out.println(ObjectSizeFetcher.getObjectSize(new C()));
    }
}</code>

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