When you pass a primitive data type, such as a char, int, float, or double, to a function then you are passing by value. That means that a copy of the data type is duplicated, and passed to the function. That means that a copy of the data type is duplicated, and passed to the function. If the function chooses to modify that value, it will be modifying the copy only.

When you pass a Java object, such as an array, a vector, or a string, to a function then you are passing by reference.So that means that if you pass an object to a function, you are passing a reference to it, not a duplicate. Any changes you make to the object's member variables will be permanent