http://www.journaldev.com/4098/java-heap-space-vs-stack-memory

Heap

Java Heap space is used by java runtime to allocate memory to Objects and JRE classes. Whenever we create any object, it’s always created in the Heap space. Garbage Collection runs on the heap memory to free the memory used by objects that doesn’t have any reference. Any object created in the heap space has global access and can be referenced from anywhere of the application.

Stack

Java Stack memory is used for execution of a thread. They contain method specific values that are short-lived and references to other objects in the heap that are getting referred from the method. Stack memory is always referenced in LIFO (Last-In-First-Out) order. Whenever a method is invoked, a new block is created in the stack memory for the method to hold local primitive values and reference to other objects in the method. As soon as method ends, the block becomes unused and become available for next method.

Stack memory size is very less compared to Heap memory.

What is difference between Heap and Stack Memory?

• Heap memory is used by all the parts of the application whereas stack memory is used only by one thread of execution.
• Whenever an object is created, it’s always stored in the Heap space and stack memory contains the reference to it. Stack memory only contains local primitive variables and reference variables to objects in heap space.
• Memory management in stack is done in LIFO manner whereas it’s more complex in Heap memory because it’s used globally.