What does final mean for a variable, method, and class in Java?

Separates final assignment, method overriding, and class inheritance while making clear that a final reference does not make an object immutable.

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A final variable can be assigned only once. If it holds an object reference, the reference cannot point to a different object after assignment, but the object may still be mutable. A final method cannot be overridden by a subclass. A final class cannot be extended. Those restrictions can express design intent, but final is not a general immutability keyword. An immutable object requires that its observable state cannot change after construction.

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Precise modifier semantics, effective finality, object mutability, and design intent.

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Core answer
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Overview
The same keyword restricts different kinds of change depending on where it is applied.
A final variable can be assigned only once. If it holds an object reference, the reference cannot point to a different object after assignment, but the object may still be mutable. A final method cannot be overridden by a subclass. A final class cannot be extended. Those restrictions can express design intent, but final is not a general immutability keyword. An immutable object requires that its observable state cannot change after construction.
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A local variable captured by a lambda must be final or effectively final, meaning it is assigned once even if the keyword is omitted. Final fields are useful in immutable designs and have Java Memory Model initialization guarantees when construction does not leak , but every referenced component must also be protected from mutation. Final methods can preserve an invariant in an extensible class, while a final class can keep its equality or security contract from being altered by a subtype.

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Saying a final reference makes the referenced object immutable.
Confusing final with finally or the obsolete finalization mechanism.
Assuming final methods cannot be overloaded.
Using final without considering mutable nested values.

What does final mean for a variable, method, and class in Java?

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