Difference between Stack and Heap in Java

Here are few differences between stack and heap memory in Java:

1) Main difference between heap and stack is that stack memory is used to store local variables and function call, while heap memory is used to store objects in Java. No matter, where object is created in code e.g. as member variable, local variable or class variable,  they are always created inside heap space in Java.

2) Each Thread in Java has there own stack which can be specified using  -Xss  JVM parameter, similarly you can also specify heap size of Java program using JVM option  -Xm s and  -Xmx  where  -Xms  is starting size of heap and  -Xmx  is maximum size of java heap. to learn more about JVM options see my post 10 JVM option Java programmer should know.

3) If there is no memory left in stack for storing function call or local variable, JVM will throw java.lang.StackOverFlowError, while if there is no more heap space for creating object, JVM will throw  java.lang.OutOfMemoryError: Java Heap Space . Read more about how to deal with  java.lang.OutOfMemoryError   in my post 2 ways to solve OutOfMemoryError in Java.

4) If you are using Recursion, on which method calls itself, You can quickly fill up stack memory. Another difference between stack and heap is that size of stack memory is lot lesser than size of  heap memory in Java.

5) Variables stored in stacks are only visible to the owner Thread, while objects created in heap are visible to all thread. In other words stack memory is kind of private memory of Java Threads, while heap memory is shared among all threads.

That's all on difference between Stack and Heap memory in Java. As I said, It’s important to understand what is heap and what is stack in Java and which kind of variables goes where, how you can run out of stack and heap memory in Java etc. Let us know if you are familiar with any other difference between stack and heap memory in java.