final

Java keyword indicating that a variable, method or class cannot be further defined or overridden or subclassed. Final means, this value won't be changed hereafter. The term final is used in a number of contexts. static final variables are close to constants in other languages, final classes may not be subclassed, final methods may not be overridden, private implies final.

Marking things final has two purposes: efficiency and safety. The compiler can perform various optimisations knowing the value cannot change. Hotspot and optimising compilers now do this anyway, whether or not you declare methods final, so using final purely for efficiency is no longer recommended. The compiler can also check to ensure you do not inadvertently attempt to change the value after computing its value once where it is defined.

A little known feature of Java is blank finals. You can declare member variables final, but not declare a value. This forces all constructors to initialise the blank final variables.

You can have both final instance and final static variables, final statics are more common. When you know the value of a constant at compile time you might as well make it static. It takes up less room, just one copy per class instead of one copy per object. It is also faster to access a static constant than an instance constant. However, if you don't know the value of the constant until instantiation time, you have to make it an instance constant.