Interface Segregation Principle (ISP)

Clients should not be forced to depend on interfaces they do not use.

Example: Imagine an interface that enforces unnecessary methods on implementing classes.

// Violation of ISP
public interface Worker {
    void work();
    void eat();
}

public class HumanWorker implements Worker {
    public void work() {
        System.out.println("Human working");
    }

    public void eat() {
        System.out.println("Human eating");
    }
}

public class RobotWorker implements Worker {
    public void work() {
        System.out.println("Robot working");
    }

    public void eat() {
        // Robots don't eat
    }
}

// Following ISP
public interface Workable {
    void work();
}

public interface Eatable {
    void eat();
}

public class HumanWorker implements Workable, Eatable {
    public void work() {
        System.out.println("Human working");
    }

    public void eat() {
        System.out.println("Human eating");
    }
}

public class RobotWorker implements Workable {
    public void work() {
        System.out.println("Robot working");
    }
}

Here, RobotWorker doesn’t need to implement eat(), respecting the ISP.

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