Q14: What are Default, Static, and Private methods in Java Interfaces?

Default Methods (Java 8+): Methods declared with default keyword providing concrete method bodies. Enables API evolution without breaking existing interface implementations.
Static Methods (Java 8+): Utility methods attached directly to the interface scope.
Private Methods (Java 9+): Encapsulated helper methods used internally inside default or static interface methods.

Modern Interface Features

public interface Logger {
    void log(String message); // Abstract

    default void logWarning(String msg) { // Default
        formatAndPrint("WARN", msg);
    }

    private void formatAndPrint(String level, String msg) { // Private (Java 9+)
        System.out.println("[" + level + "]: " + msg);
    }
}

💡 Default methods provide implementation logic while private methods cleanly isolate helper logic.

Key Takeaways

default methods allow adding new interface methods safely.
private methods encapsulate shared internal logic inside interfaces.

Knowledge Check

Why were default methods introduced in Java 8?

Q14: What are Default, Static, and Private methods in Java Interfaces?

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