State is a behavioral design pattern, in which a class behavior changes based on its state. In State pattern there are objects which represent various states and a context object whose behavior varies as its state object changes.

In the example below there is a State interface defining an action and concrete classes implementing the State interface. Context is a class which carries a State. StatePatternDemo will use Context and state objects to demonstrate change in Context behavior based on type of state it is in.

Step 1 : Create an interface

public interface State {
    void doAction(Context context);
}

Step 2 : Create concrete classes implementing the same interface

public class StartState implements State {
    @Override
    public void doAction(Context context) {
        System.out.println("Player is in start state");
        context.setState(this);
    }

    public String toString() {
        return "Start State";
    }
}

public class StopState implements State {
    @Override
    public void doAction(Context context) {
        System.out.println("Player is in stop state");
        context.setState(this);
    }

    public String toString() {
        return "Stop State";
    }
}

Step 3 : Create Context class

public class Context {
    private State state;

    public State getState() {
        return state;
    }

    public void setState(State state) {
        this.state = state;
    }
}

Step4 : Use the Context to see changes in behavior when State changes

public class StatePatternDemo {
    public static void main(String[] args) {
        Context context = new Context();

        StartState startState = new StartState();
        startState.doAction(context);
        System.out.println(context.getState());

        StopState stopState = new StopState();
        stopState.doAction(context);
        System.out.println(context.getState());
    }
}

The output will be : 

Player is in start state
Start State
Player is in stop state
Stop State