Playing with JVM / Java Heap Size.

Java programs executes in JVM uses Heap of memory to manage the data. If your Java program requires a large amount of memory, it is possible that the virtual machine will begin to throw OutOfMemoryError instances when attempting to instantiate an object. The default heap size if 1 MB and can increase as much as 16 MB.

Setting/Increase JVM heap size

It is possible to increase heap size allocated by the Java Virtual Machine (JVM) by using command line options.

Following are few options available to change Heap Size.

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-Xms<size>        set initial Java heap size -Xmx<size>        set maximum Java heap size -Xss<size>        set java thread stack size

For example, you can set minimum heap to 64 MB and maximum heap 256 MB for a Java program HelloWorld.

1	java -Xms64m -Xmx256m HelloWorld

Getting / Reading default heap size

It is possible to read the default JVM heap size programmatically by using totalMemory() method of Runtime class. Use following code to read JVM heap size.

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public class GetHeapSize {     public static void main(String[]args){           //Get the jvm heap size.         long heapSize = Runtime.getRuntime().totalMemory();           //Print the jvm heap size.         System.out.println("Heap Size = " + heapSize);     } }