Our principal goal as programmers is to reduce complexity. At any point in a program, we can reason about the state of a constant trivially -- its state is the state upon assignment. By contrast, the state of a variable can change endlessly.
With judicious use, immutable objects can lead to quicker execution speed and lower memory usage. The hash value of a String, the query parameters of an immutable URL, and the distance traced by an immutable sequence of points are all immutable as well. We can cache their values for later use instead of recompute them on every access. We can also share an immutable object with clients without requiring those clients to defensively copy it.
An immutable value is safe in many ways. For example, String is immutable and so its hashCode value is immutable. Consequently, it is safe to use as a String as a key in a Map: The lower order bits of that hash will never change, and so an inserted key will never reside in the wrong bucket. An immutab