Java Exception: "java.lang.OutOfMemoryError: Java heap space"

This section provides a tutorial example on how JVM expands the Heap space to allocate more objects and leads to the 'java.lang.OutOfMemoryError: Java heap space' Java exception, if it is not allowed to expand any more.

First, let's use the following simple program, HeapMemoryCrash.java, to observe what will happen when the Heap runs out of memory:

/* HeapMemoryCrash.java
 * Copyright (c) 2018, HerongYang.com, All Rights Reserved.
 */
class HeapMemoryCrash {
   public static void main(String[] a) {
      int max = 1000;
      Object[] arr = new Object[max];
      heapCheck();
      for (int n=0; n<max; n++) {
         arr[n] = new long[10*1024*128];
         System.out.println((n+1)+": "
            +((n+1)*10)+" MB of objects created.");
         heapCheck();
      }
   }
   public static void heapCheck() {
      Runtime rt = Runtime.getRuntime();
      rt.gc();
      long total = rt.totalMemory();
      long free = rt.freeMemory();
      long used = total - free;
      java.io.Console con = System.console();
      con.format("Total memory: %s%n",total);
      con.format(" Free memory: %s%n",free);
      con.format(" Used memory: %s%n",used);
      String str = con.readLine("Press ENTER key to continue: ");
   }
}

This program is designed to:

Compile and run with HotSpot JVM 1.8:

C:\herong>\progra~1\java\jdk1.8.0\bin\javac HeapMemoryCrash.java

C:\>\progra~1\java\jdk1.8.0\bin\java -Xms20m -Xmx50m HeapMemoryCrash
Total memory: 20447232
 Free memory: 20188720
 Used memory: 258512
Press ENTER key to continue:
1: 10 MB of objects created.
Total memory: 26152960
 Free memory: 15377464
 Used memory: 10775496
Press ENTER key to continue:
2: 20 MB of objects created.
Total memory: 50724864
 Free memory: 29463808
 Used memory: 21261056
Press ENTER key to continue:
3: 30 MB of objects created.
Total memory: 50724864
 Free memory: 18978032
 Used memory: 31746832
Press ENTER key to continue:
4: 40 MB of objects created.
Total memory: 50724864
 Free memory: 8492256
 Used memory: 42232608
Press ENTER key to continue:
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
   at HeapMemoryCrash.main(HeapMemoryCrash.java:10)

The output confirms that:

Last update: 2018.

Table of Contents

 About This Book

Heap Memory Area and Size Control

Java Exception: "java.lang.OutOfMemoryError: Java heap space"

 Memory Allocation Limits on Windows Systems

 OutOfMemoryError Comparison of HotSpot and JRockit

 JVM Garbage Collection Logging

 Introduction of Garbage Collectors

 Serial Collector - "+XX:+UseSerialGC"

 Parallel Collector - "+XX:+UseParallelGC"

 Concurrent Mark-Sweep (CMS) Collector - "+XX:+UseConcMarkSweepGC"

 Garbage First (G1) Collector - "+XX:+UseG1GC"

 Object References and Garbage Collection

 Garbage Collection Performance Test Program

 Performance Tests on Serial Collector

 Performance Tests on Parallel collector

 Performance Tests on Concurrent collector

 Performance Tests on G1 collector

 Garbage Collection Performance Test Summary

 Outdated Tutorials

 References

 Full Version in PDF/EPUB