get byte or memory size of array,list,collections in java

In java lot of time we will come across the scenerio where in which we need to find the how much memory used by given list.

The ArrayList holds a pointer to a single Object array, which grows as the number of elements exceed the size of the array. The ArrayList's underlying Object array grows by about 50% whenever we run out of space.

ArrayList also writes out the size of the underlying array, used to recreate an identical ArrayList to what was serialized.

sample code to get the memory size the collection in bytes

	import java.io.ByteArrayOutputStream;
	import java.io.IOException;
	import java.io.ObjectOutputStream;
	import java.io.Serializable;
	import java.util.ArrayList;
	import java.util.LinkedList;
	import java.util.List;
	/**
	* @author Uttesh Kumar T.H.
	*/
	public class FindSize {
	static long numberOfRecords=1000;
	public static void main(String[] args) throws IOException {
	testPrimitives(new LinkedList<Integer>());
	testPrimitives(new ArrayList<Integer>());
	testObjects(new LinkedList<User>());
	testObjects(new ArrayList<User>());
	}
	public static void populateListOfPrimitives(List<Integer> list) {
	for (int i = 0; i < numberOfRecords; i++) {
	list.add(new Integer(i * 10));
	}
	}
	public static void populateListOfObjects(List<User> list) {
	User user = null;
	for (int i = 0; i < numberOfRecords; i++) {
	user = new User();
	user.setName("user_"+i);
	user.setPassword("password_"+i);
	list.add(user);
	}
	}
	public static void testPrimitives(List<Integer> list) throws IOException {
	System.out.println("Primitives "+list.getClass().getSimpleName());
	populateListOfPrimitives(list);
	long size = getBytesFromList(list);
	printInUnits(size);
	}
	public static void testObjects(List<User> list) throws IOException {
	System.out.println("Objects "+list.getClass().getSimpleName());
	populateListOfObjects(list);
	long size = getBytesFromList(list);
	printInUnits(size);
	}
	public static long getBytesFromList(List list) throws IOException {
	ByteArrayOutputStream baos = new ByteArrayOutputStream();
	ObjectOutputStream out = new ObjectOutputStream(baos);
	out.writeObject(list);
	out.close();
	return baos.toByteArray().length;
	}
	public static void printInUnits(long length) {
	System.out.println("list size is :: " + length / 1000000000 + " GB");
	System.out.println("list size is :: " + length / 1000000 + " MB");
	System.out.println("list size is :: " + length / 1000 + " kB");
	System.out.println("list size is :: " + length + " byte");
	}
	}
	class User implements Serializable{
	String name;
	String password;
	public String getName() {
	return name;
	}
	public void setName(String name) {
	this.name = name;
	}
	public String getPassword() {
	return password;
	}
	public void setPassword(String password) {
	this.password = password;
	}
	}

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