What to Do When Java is Not Garbage Collecting Memory?

What should I do if Java is not properly garbage collecting memory?

// Example of creating objects that should be garbage collected
for (int i = 0; i < 10000; i++) {
    Object obj = new Object(); // These objects are eligible for garbage collection
}

Garbage collection in Java is a critical process that automatically frees up memory used by objects that are no longer needed by the program. However, there are instances when it seems that Java fails to collect these objects, leading to memory leaks or excessive memory usage. Understanding how garbage collection works and what might prevent it from functioning optimally is essential for maintaining an efficient Java application.

// Setting an object reference to null
MyObject myObj = new MyObject();
// Later in the code
myObj = null; // Now eligible for garbage collection

Causes

• Insufficient memory available for the Java Virtual Machine (JVM);
• References still exist to objects that seem unused, preventing their collection;
• Using static fields inappropriately holds onto objects and complicates garbage collection;
• Long-lived threads that hold large objects prevent collection until threads terminate.

Solutions

• Use profiling tools to monitor memory usage and identify potential leaks;
• Explicitly set large objects to null once they’re no longer needed;
• Consider revisiting the use of static fields within your classes;
• Adjust the JVM memory parameters (e.g., `-Xms`, `-Xmx`) to better handle the application’s memory requirements.

Mistake: Forgetting to nullify object references when they are no longer needed.

Solution: Always set object references to null when you are done using them to help the garbage collector identify unused objects.

Mistake: Ignoring memory leaks caused by static references.

Solution: Minimize the use of static references for objects that can grow over time.

Mistake: Failing to monitor or profile memory usage during development.

Solution: Utilize tools like VisualVM or JProfiler to actively monitor memory and garbage collection during development.