You have to specify the heap size whenever you run your program. If you are executing on the command line, whenever you execute using "java " include a parameter: "-Xmx4g -Xmx4g" or whatever you want your heap size to be. The flag Xmx specifies the maximum memory allocation pool for a Java Virtual Machine (JVM), while Xms specifies the initial memory allocation pool. The Xms flag has no default value, and Xmx typically has a default value of 256 MB. A common use for these flags is when you encounter a java.lang.OutOfMemoryError. If you are dealing with large data sets, then its always better to initialise your Java Collections (ex.
Java Arraylist) with the correct size.
