Solving Exception in Thread AWT-EventQueue-0 Java Heap Space OutOfMemoryError

In this guide, we'll walk you through the steps to troubleshoot and resolve the 'Exception in Thread AWT-EventQueue-0' Java Heap Space OutOfMemoryError. If you're a developer encountering this issue, this guide will help you understand the root cause of the problem and provide step-by-step solutions to fix it.

Table of Contents

Understanding 'Exception in Thread AWT-EventQueue-0'

The 'Exception in Thread AWT-EventQueue-0' error occurs when an unhandled exception is thrown in the AWT event dispatch thread. AWT (Abstract Window Toolkit) is a Java library used for creating graphical user interfaces (GUIs). The AWT event dispatch thread, also known as the EventQueue, is responsible for managing and dispatching AWT events to the appropriate event handlers.

When an exception is thrown in the AWT event dispatch thread, it causes the thread to terminate, resulting in the 'Exception in Thread AWT-EventQueue-0' error.

Causes of Java Heap Space OutOfMemoryError

The Java Heap Space OutOfMemoryError is an error that occurs when the Java Virtual Machine (JVM) runs out of memory. This error is usually caused by one of the following reasons:

Insufficient Heap Space: The JVM has a limited amount of memory allocated for the heap, which is used for storing objects created by your application. If your application creates too many objects or large objects that exceed the available heap space, the JVM will run out of memory and throw an OutOfMemoryError.

Memory Leaks: Memory leaks occur when objects are no longer needed by the application but are not properly released, causing the JVM to retain them in the heap. Over time, these unreleased objects accumulate, consuming more heap space and eventually leading to an OutOfMemoryError.

Step-by-Step Solution

Step 1: Analyze Memory Usage

To troubleshoot the OutOfMemoryError, start by analyzing your application's memory usage. You can use tools like VisualVM or JConsole to monitor the heap usage and garbage collection activity in real time.

Step 2: Increase Java Heap Space

If the heap usage analysis reveals that your application requires more heap space than currently allocated, you can increase the heap size by adjusting the JVM's memory settings:

  1. Open the command prompt or terminal.
  2. Set the heap size using the -Xmx and -Xms options. For example, to set the maximum heap size to 512MB, use -Xmx512m. To set the initial heap size to 256MB, use -Xms256m.
  3. Run your application with the new heap size settings.


java -Xmx512m -Xms256m -jar my_application.jar

Step 3: Optimize Code for Memory Efficiency

If increasing the heap space does not resolve the OutOfMemoryError, you may need to optimize your code to use memory more efficiently:

  1. Review your code for any memory-intensive operations or large data structures.
  2. Consider using more space-efficient data structures or algorithms.
  3. Release resources (e.g., close file streams, database connections, etc.) when they are no longer needed.

Step 4: Use Garbage Collection Tools

If the OutOfMemoryError persists, consider using garbage collection (GC) tools to help identify and resolve memory leaks in your application:

  1. Enable GC logging by adding the -verbose:gc option when running your application: java -verbose:gc -jar my_application.jar
  2. Analyze the GC logs to identify memory leaks or inefficiencies in your application's memory management.
  3. Use tools like Eclipse Memory Analyzer (MAT) or VisualVM to identify the root cause of memory leaks and fix them in your code.


1. What is Java Heap Space?

Java Heap Space is a part of the Java Virtual Machine (JVM) memory where objects created by your application are stored. It is a shared resource used by all Java applications running on the same JVM.

2. How is the Java Heap Space allocated?

The Java Heap Space is allocated by the JVM at startup, based on the -Xmx and -Xms command-line options. The -Xmx option sets the maximum heap size, while the -Xms option sets the initial heap size.

3. How can I increase the Java Heap Space?

You can increase the Java Heap Space by adjusting the -Xmx and -Xms command-line options when running your Java application. For example, to set the maximum heap size to 512MB, use -Xmx512m. To set the initial heap size to 256MB, use -Xms256m.

4. How do I find memory leaks in my Java application?

You can use tools like VisualVM, JConsole, or Eclipse Memory Analyzer (MAT) to monitor your application's memory usage, analyze garbage collection logs, and identify memory leaks.

5. What are some best practices for preventing memory leaks in Java?

Some best practices for preventing memory leaks in Java include:

  1. Properly release resources (e.g., close file streams, database connections, etc.) when they are no longer needed.
  2. Use weak references for objects that do not need to be kept in memory.
  3. Be mindful of anonymous inner classes, as they can inadvertently hold references to their enclosing class.
  4. Use a memory profiler to monitor your application's memory usage and identify potential memory leaks.

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