Final keyword in Java

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 In Java, the final keyword can be applied to variables, methods, and classes. Its meaning differs slightly depending on where it is used:

  1. Final variables: A final variable cannot be reassigned a new value once it has been initialized. It is often used to declare constants. For example:

    java
    final int MAX_SIZE = 10;

  2. Final methods: A final method cannot be overridden by a subclass. This is useful when you want to prevent a subclass from changing the behavior of a method. For example:

    java
    class Parent {
    final void doSomething() {
        // ...
    }
}

class Child extends Parent { 
  3. // Compiler error: Cannot override the final method from Parent void doSomething() { // ... } }

  4. Final classes: A final class cannot be subclassed. This is useful when you want to prevent other classes from extending your class. For example:

    java
    final class MyClass {
    // ...
} 
  5. // Compiler error: Cannot extend final class MyClass class MySubclass extends MyClass { // ... }

In summary, the final keyword is used to declare entities that cannot be modified or extended.

  1. Final parameters: A final parameter cannot be reassigned within the method body. This can be useful when you want to ensure that the parameter value is not changed by mistake. For example:

    java
    void doSomething(final int param) {
    // Compiler error: Cannot assign a value to final variable 'param'
    param = 10;

    // ...
}

  2. Final vs. Immutable: While a final variable cannot be reassigned, it does not necessarily mean that the object it refers to is immutable. For example, if a final variable refers to a mutable object such as an ArrayList, the contents of the ArrayList can still be modified even though the reference itself cannot be changed.

    On the other hand, an immutable object is one that cannot be modified once it has been created. Examples of immutable objects in Java include String and the wrapper classes for primitive types (e.g. Integer, Double, etc.).

  3. Final fields: A final field is a class-level variable that cannot be reassigned after it has been initialized. It is often used to declare constants at the class level. For example:

    java
    class MyClass {
    static final int MAX_SIZE = 10;
    final int id;

    MyClass(int id) {
        this.id = id;
    }

    // ...
}

    Note that a final field can be initialized in one of two ways: either directly in the field declaration, or in a constructor. If a final field is not initialized in the field declaration, it must be initialized in every constructor of the class.

  4. Benefits of using final: Using the final keyword can improve code clarity and prevent bugs. By marking variables, methods, and classes as final, you can communicate to other developers that these entities should not be modified or extended. This can make your code easier to reason about and less error-prone.

I hope this additional information helps!


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