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.
-Xmx<size> set maximum Javaheapsize
-Xss<size> setjavathread stack size
For example, you can set minimum heap to 64 MB and maximum heap 256 MB for a Java program HelloWorld.
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.