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Sharath Kumar
Sharath Kumar

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What is OutOfMemoryError in Java?

#outofmemoryerror #java #jvm

In Java applications, memory is managed by the Java Virtual Machine (JVM). The JVM automatically allocates and releases memory using Garbage Collection. However, when the JVM cannot allocate enough memory for new objects or resources, it throws an error known as OutOfMemoryError.

OutOfMemoryError (OOM) occurs when the Java application runs out of memory and the JVM cannot allocate additional space for objects or data structures.

This is a common issue in large applications, especially when memory usage is not managed properly.

Definition

OutOfMemoryError is a runtime error that occurs when the Java Virtual Machine cannot allocate memory for new objects because the available memory is exhausted.

It belongs to the java.lang package and is a subclass of the Error class.

Example:

public class MemoryExample {

    public static void main(String[] args) {

        int[] arr = new int[Integer.MAX_VALUE];

    }

}
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This program tries to allocate a huge array which exceeds JVM memory limits, resulting in an OutOfMemoryError.

Common Types of OutOfMemoryError

1. Java Heap Space

Occurs when the heap memory is full and the JVM cannot create new objects.

Example error:

java.lang.OutOfMemoryError: Java heap space
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Common causes:

  • Creating too many objects
  • Memory leaks
  • Large data structures

2. GC Overhead Limit Exceeded

Occurs when the Garbage Collector spends too much time collecting memory but recovers very little space.

Example error:

java.lang.OutOfMemoryError: GC overhead limit exceeded
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3. Metaspace

Occurs when class metadata storage exceeds available Metaspace memory.

Example error:

java.lang.OutOfMemoryError: Metaspace
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This may happen when applications load too many classes dynamically.

4. Direct Buffer Memory

Occurs when native memory used by NIO buffers is exhausted.

Example:

java.lang.OutOfMemoryError: Direct buffer memory
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5. Unable to Create New Native Thread

Occurs when the JVM cannot create new threads because system resources are exhausted.

Example:

java.lang.OutOfMemoryError: unable to create new native thread
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Common Causes of OutOfMemoryError

Several factors can lead to this error:

  • Memory leaks in the application
  • Creating very large objects
  • Excessive object creation
  • Improper caching strategies
  • Large collections not being cleared
  • Too many threads running simultaneously

How to Prevent OutOfMemoryError

Developers can reduce the chances of this error by following best practices:

✔ Optimize object creation
✔ Use proper data structures
✔ Close unused resources
✔ Monitor memory usage
✔ Configure JVM memory parameters

Example JVM configuration:

-Xms512m
-Xmx2048m
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Where:

  • Xms → Initial heap size
  • Xmx → Maximum heap size

Real-World Scenario

In large enterprise applications such as Spring Boot microservices or high-traffic backend systems, improper memory management can lead to OutOfMemoryError, causing application crashes or downtime.

Therefore, understanding JVM memory management and Garbage Collection is crucial for Java developers.

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