F.11 final Instance Variables

The principle of least privilege is fundamental to good software engineering. In the context of an application, it states that code should be granted only the amount of privilege and access that it needs to accomplish its designated task, but no more. This makes your programs more robust by preventing code from accidentally (or maliciously) modifying variable values and calling methods that should not be accessible.

Let’s see how this principle applies to instance variables. Some of them need to be modifiable and some do not. You can use the keyword final to specify that a variable is not modifiable (i.e., it’s a constant) and that any attempt to modify it is an error. For example,

private final int INCREMENT

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