why there is a difference in behavior for copying contents in primitive and non primitive type?

Primitive type includes Number, String, Boolean. Primitive variable stores primitive value.

Whereas the Non-primitive type aka Reference type are any instantiable class as well as arrays. Example: Array, Object, function. Reference variables store addresses.

Assignment:

• copies the contents of RHS variable into LHS variable
• primitives: the primitive value is copied (Call by value)
• references: the address is copied (Call by reference)
• implications: for references the object is not copied, it is shared (reference variables are aliases)

1. Call by value:

In Copy/call by value, when we assign a variable to an other variable, variable data is passed to another variable . Both the variables refers two different memory locations. consider the below example. No memory location is shared, just the data is copied to another memory location. All primitive data by default follows call by value.

2. Call by reference

In call by reference, no new memory is created/allocate when trying to copy. Just an reference is create which points to the old memory. All composite datatypes follow call by reference by default. Lets look at the example below for better understanding.

This is because no new memory is allocated arr1 and arr2 points to same memory