What is OutOfMemoryError ?
- The OutOfMemoryError is thrown by JVM, when JVM does not have enough available memory, to allocate.
- OutOfMemoryError falls into the error category (Exception class hierarchy) of VirtualMachineError.
Exception class hierarchy
- We have shown some of exception classes in Fig 1.
The simulation of OutOfMemoryError:
- We will allocate large chunk of memory, which will exhaust heap memory storage.
- We will keep on allocating the memory (in below program) and point will reach, when JVM will not have enough memory to allocate, then.
- OutOfMemoryError will be thrown
- We will catch out of memory error (Note: we can not recover from error conditions e.g. OutOfMemoryError, StackOverflowError etc.).
- We can log the OutOfMemoryError (e.g to generate the statistics etc).
Program to simulate or generate OutOfMemoryError in java.
package org.learn;public class SimulateOutOfMemoryError { public static void main(String[] args) throws Exception { int dummyArraySize = 15; System.out.println("Max JVM memory: " + Runtime.getRuntime().maxMemory()); long memoryConsumed = 0; try { long[] memoryAllocated = null; for (int loop = 0; loop < Integer.MAX_VALUE; loop++) { memoryAllocated = new long[dummyArraySize]; memoryAllocated[0] = 0; memoryConsumed += dummyArraySize * Long.SIZE; System.out.println("Memory Consumed till now: " + memoryConsumed); dummyArraySize *= dummyArraySize * 2; Thread.sleep(500); } } catch (OutOfMemoryError outofMemory) { System.out.println("Catching out of memory error"); //Log the information,so that we can generate the statistics (latter on). throw outofMemory; } }} |
Output of OutOfMemoryError (usage of JVM memory)
Max JVM memory: 926941184Memory Consumed till now: 960Memory Consumed till now: 29760Memory Consumed till now: 25949760Catching out of memory errorException in thread "main" java.lang.OutOfMemoryError: Java heap space at org.learn.SimulateOutOfMemoryError.main(SimulateOutOfMemoryError.java:13) |