In Java what is the best way to determine the size of an object

0 votes

let's say I have an application that can read in a CSV file with piles of data rows. I give the user a summary of the number of rows based on types of data, but I want to make sure that I don't read in too many rows of data and cause OutOfMemoryErrors. Each row translates into an object. Is there an easy way to find out the size of that object programmatically? Is there a reference that defines how large primitive types and object references are for a VM?

Right now, I have code that says read up to 32,000 rows, but I'd also like to have code that says read as many rows as possible until I've used 32MB of memory. Maybe that is a different question, but I'd still like to know.

Nov 22, 2018 in Java by Neha
• 6,300 points

2 answers to this question.

0 votes

Please check the below code to arrive at the solution

You can use the java.lang.instrument package

Compile and put this class in a JAR:

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);

Add the following to your MANIFEST.MF:

Premain-Class: ObjectSizeFetcher

Use getObjectSize:

public class C {
    private int x;
    private int y;

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

Invoke with:

java -javaagent:ObjectSizeFetcherAgent.jar C

Hope it helps!!

If you need to know more about Java, join our Java online course today.

Thank you

answered Nov 22, 2018 by Frankie
• 9,830 points
0 votes

I happened to find a java class "", already in jdk, which is easy to use and seems quite useful for determining the size of an object.

System.out.println(ObjectSizeCalculator.getObjectSize(new<String>(12000, 0.6f, -1)));

System.out.println(ObjectSizeCalculator.getObjectSize(new HashMap<String, Integer>(100000)));


System.out.println(ObjectSizeCalculator.getObjectSize(new int[]{1, 2, 3, 4, 5, 6, 7 }));

System.out.println(ObjectSizeCalculator.getObjectSize(new int[100]));

answered Aug 19, 2019 by Sirajul
• 59,230 points

Related Questions In Java

0 votes
2 answers

What is the easiest way to iterate through the characters of a string in Java?

There are two approaches to this: for(int i ...READ MORE

answered Aug 19, 2019 in Java by Sirajul
• 59,230 points
+1 vote
3 answers

What is the syntax to declare and initialize an array in java?

You can use this method: String[] strs = ...READ MORE

answered Jul 25, 2018 in Java by samarth295
• 2,220 points
0 votes
2 answers

What's the best way to check if a String represents an integer in Java?

You can also use regular expression. str.matches("-?\\d+"); It will ...READ MORE

answered Aug 9, 2018 in Java by Daisy
• 8,120 points
0 votes
2 answers

what is the best way to convert an ArrayList to a String

You could probably use the Joiner class ...READ MORE

answered Aug 19, 2019 in Java by Sirajul
• 59,230 points
0 votes
1 answer

Why Java Code in Hadoop uses own Data Types instead of basic Data types?

Hadoop provides us Writable interface based data ...READ MORE

answered Apr 15, 2018 in Big Data Hadoop by kurt_cobain
• 9,390 points
0 votes
1 answer

Converting String and Float Data-types

Using Java’s Float class. float f = Float.parseFloat("25"); String s = ...READ MORE

answered May 9, 2018 in Java by developer_1
• 3,320 points
+5 votes
4 answers

How to execute a python file with few arguments in java?

You can use Java Runtime.exec() to run python script, ...READ MORE

answered Mar 27, 2018 in Java by DragonLord999
• 8,450 points

edited Nov 7, 2018 by Omkar 79,892 views
+1 vote
1 answer

How to handle drop downs using Selenium WebDriver in Java

First, find an XPath which will return ...READ MORE

answered Mar 27, 2018 in Selenium by nsv999
• 5,500 points
+1 vote
4 answers

What is a simple way to repeat a string in java?

There is already answer wriiten using StringBuilder ...READ MORE

answered Dec 16, 2020 in Java by Rajiv
• 8,910 points
0 votes
1 answer

What is the maximum Java heap size of a 32-bit JVM on a 64-bit OS?

32-bit JVMs which expect to have a ...READ MORE

answered Nov 15, 2018 in Java by Frankie
• 9,830 points
webinar_success Thank you for registering Join Edureka Meetup community for 100+ Free Webinars each month JOIN MEETUP GROUP