Question

When a variable is noted to be immutable, what does this mean? What is the advantage/ disadvantage of immutable variables?

Answer 1

In simple terms, immutability means unchanging over time or unable to be changed.Thus,Immutable variables simply means that their values can't be modified once after it is created.In other words,you can say they are the constants.
Advantages of immutabilty:
1. It is easier to deal with and create.
2. Since their values are not modifiable they are easy to share them across various functions
3. They do not have a defensive copy, so their usage is side effect free.
4. They simplifies debugging as they have only one value.

Disadvantages:
1.May be the reason for access memory usage sometimes.
2.The updates of immutable variables tend to require multiple allocations and can lead to excessive garbage collection work.
3.There might be difficulty in propagating changes, particularly when dealing with objects with identity.
4.The immutable data might be slower than their mutable counter parts.