Memory Leaks in Java

In programming, a memory leak happens when a program keeps using memory but does not give it back when it's done. It simply means the program slowly uses more and more memory, which can make things slow and even stop working.

Working of Memory Management in Java

• Java has automatic garbage collection, which simply means that Java can automatically free up memory for objects that are no longer in use or no longer needed.
• But if our program creates many objects but keeps references to them even if they are not needed, the garbage collector cannot destroy those objects. If memory use grows beyond the allowed limit, the program will crash.

Note: If an object is no longer needed, it is important to remove references to it so the garbage collector can free its memory.

Why Do Memory Leaks Happen in Java?

We know that Java cleans up memory automatically with the help of the garbage collector, but still, memory leaks can happen, this happens because our program keep holding onto things that are no longer needed. Our Java program still remembers these objects and thinks they are important and that's why it does not remove them and this wastes memory and causes problems.

import java.util.ArrayList;
import java.util.List;

public class GFG{
    
    public static void main(String[] args){
        
        List<byte[]> list = new ArrayList<>();

        while (true) {
            // Each iteration creates a 1 MB object
            list.add(new byte[1024 * 1024]);
        }
    }
}

Output:

Explanation: The program keeps creating 1 MB byte arrays and stores all of them in the list. Since the list holds references to every array, the garbage collector cannot free the memory. As the list grows, heap memory fills up and eventually causes an OutOfMemoryError.

Tools to Find Memory Leaks

There are multiple tools that help us to detect memory leaks by showing which object is using the most memory, and the list of such tools are listed below:

• VisualVM (comes with JDK)
• Eclipse Memory Analyzer (MAT)
• Java Mission Control
• YourKit Java Profiler

What Happens If Memory Keeps Leaking?

If our program keep on leaking memory it means the program will use up all the memory as much as it can use. After some time, the program will stop working and will show an error like this:

java.lang.OutOfMemoryError: Java heap space

This means Java ran out of memory to create new things it needs.

How to Avoid Memory Leaks?

We can avoid memory leaks by keeping few things in our mind which is listed below:

• Stop keeing things that we do not need in our program do not initialize unnecessary variables and list items to null.
• Do not let lists or caches keep growing forever without removing old stuff.
• It is always recommended to close files and database connections when we are done with them.
   

Memory Management in C vs Java

The main difference between memory management in c and memory management in Java is listed below:

• In C language, programmers manually allocate and free memory. If a programmer forgets to free memory then it causes a memory leak.
• In Java language, memory is managed automatically with the help of a garbage collector. The task of garbage collector is to find objects that are no longer used and free up their memory.