Call by value and call by reference is a mechanism of passing argument while calling a method. When we pass an argument to a method while calling, it is passed using either call by value or call by reference mechanism. Since java uses only call by value mechanism, so we will discuss only call by value mechanism in this tutorial.

Java is strictly call by value. However, this can be confusing because objects seem to exhibit "by reference" behavior. What really happens is: When you pass a primitive type (like int, double, boolean), Java copies the actual value of the variable.

Only call by value is used in Java while passing reference variables as well. It makes a duplicate of the references and provides them to the methods as useful. Creating a copy of a reference is harmless because it points to the same object's address. However, if a new item is added to the reference list, it will not be reflected.

In java, the reference of an object is itself a value. In call by value mechanism, this value (reference) is itself passed to called method. The program below shows the call by value mechanism for primitive type variables in java. The changes made in called method will not be reflected in calling method. class CallByValue { static int a = 20;