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A final class in Java is a class declared with the final modifier, which strictly prohibits inheritance. Once a class is marked as final, it becomes a terminal node in the class hierarchy, meaning the Java compiler will reject any attempt by another class to extend it. 
public final class TerminalClass {
    // Class members
}

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Core Mechanics and Compiler Behavior

Inheritance Restriction Attempting to use the extends keyword on a final class results in a strict compile-time error (cannot inherit from final). 
public final class BaseComponent {
}

// COMPILER ERROR: Cannot inherit from final 'BaseComponent'
public class SubComponent extends BaseComponent { 
}
Method Implication and Binding Because a final class cannot be subclassed, it is impossible for any of its instance methods to be overridden. Consequently, the compiler can safely use static binding (early binding) for all method calls on instances of the class. Explicitly declaring methods as final inside a final class is syntactically valid but entirely redundant. Field Mutability Applying the final modifier to a class declaration does not cascade to its members. Instance variables within a final class remain fully mutable unless they are individually declared with the final modifier. 
public final class StateContainer {
    // This field can still be modified after instantiation
    public int mutableCounter = 0; 
    
    // This field is strictly immutable
    public final String id = "STATIC_ID"; 
}
Instantiation The final modifier has no impact on object creation. A final class behaves identically to a standard class regarding instantiation and can be instantiated normally using the new keyword, provided its constructors are accessible.

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Modifier Conflicts

A class cannot be declared as both abstract and final. This is a logical contradiction enforced by the compiler: the abstract modifier dictates that a class must be subclassed to implement its abstract methods, whereas the final modifier dictates that a class cannot be subclassed. 
// COMPILER ERROR: Illegal combination of modifiers: 'abstract' and 'final'
public abstract final class InvalidClass {
}
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