状态模式

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

class StateA implements State {
    public void Handle(Context context) {
    context.State = new StateB();
    }
}
class StateB implements State {
    public void Handle(Context context) {
    context.State = new StateC();
    }
}
class StateC implements State {
    public void Handle(Context context) {
    context.State = new StateA();
    }
}
class Context {
    private State state;
    public Context(State state) {
        this.state = state;
    }
    public void Request() {
        state.Handle(this);
    }
    public static void main(String[] args) {
        Context c = new Context(new StateA());
        c.Request();
        c.Request();
        c.Request();
    }
}
}

/* 该模式是用于消除复杂的switch/if-else结构，并保障OCP原则 */
public class 状态模式 {
    public static void main(String[] args) {
        PaintBoard paintBoard = new PaintBoard();
        
        System.out.println("Push test: ");
        System.out.println("Paint board current color:" + paintBoard.getCurrentColor());
        for(int i=0; i<3; i++) {
            System.out.printf("%s ---push---> ", paintBoard.getCurrentColor());
            paintBoard.push();
            System.out.println(paintBoard.getCurrentColor());
        }
        
        System.out.println("Pull test: ");
        System.out.println("Paint board current color:" + paintBoard.getCurrentColor());
        for(int i=0; i<3; i++) {
            System.out.printf("%s ---pull---> ", paintBoard.getCurrentColor());
            paintBoard.pull();
            System.out.println(paintBoard.getCurrentColor());
        }
    }
}

class PaintBoard {
    private State state = new RedState();
    
    public String getCurrentColor() {
        return state.name();
    }
    public void setState(State state ) {
        this.state = state;
    }
    public void push() {
        state.push(this);
    }
    public void pull() {
        state.pull(this);
    }
}

//借口
interface State {
    void push(PaintBoard paintBoard);
    void pull(PaintBoard paintBoard);
    String name();
}

//下面三种颜色分别实现该接口
class RedState implements State {

    @Override
    public void push(PaintBoard paintBoard) {
        paintBoard.setState(new GreenState());
    }

    @Override
    public void pull(PaintBoard paintBoard) {
        paintBoard.setState(new BlueState());
    }

    @Override
    public String name() {
        return "RED";
    }
    
}
class GreenState implements State {

    @Override
    public void push(PaintBoard paintBoard) {
        paintBoard.setState(new BlueState());
    }

    @Override
    public void pull(PaintBoard paintBoard) {
        paintBoard.setState(new RedState());
    }

    @Override
    public String name() {
        return "GREEN";
    }
    
}
class BlueState implements State {

    @Override
    public void push(PaintBoard paintBoard) {
        paintBoard.setState(new RedState());
    }

    @Override
    public void pull(PaintBoard paintBoard) {
        paintBoard.setState(new GreenState());
    }

    @Override
    public String name() {
        return "BLUE";
    }
    
}