In Java size of heap memory by default is 64MB, however if your application holds many objects then you might get the following exception,
java.lang.OutOfMemoryError: Java heap space
There is a simple solution for the problem and it would be reached by increasing your heap size on runtime with the following command,
$ java -Xms256m -Xmx1024m YourClassName/JarFileName
The first parameter defines the minimum heap size and the second parameter sets the maximum size of heap for your application.