状态接口

public interface State {//状态接口

    void insertQuarter();//投币

    void ejectQuarter();//退币

    void turnCrank();//按下“出纸巾”按钮

    void dispense();//出纸巾
}

有纸巾类

public class HasQuarterState implements State {
    private TissueMachine tissueMachine;

    @Override
    public void insertQuarter() {}

    @Override
    public void ejectQuarter() {
        tissueMachine.setState(tissueMachine.getNoQuarterState());
    }

    @Override
    public void turnCrank() {}

    @Override
    public void dispense() {}
}

没有纸巾类

public class NoQuarterState implements State {
    private TissueMachine tissueMachine;

    @Override
    public void insertQuarter() {
        tissueMachine.setState(tissueMachine.getHasQuarterState());
    }

    @Override
    public void ejectQuarter() {}

    @Override
    public void turnCrank() {}

    @Override
    public void dispense() {}
}

售完类

public class SoldOutState implements State {
    private TissueMachine tissueMachine;

    @Override
    public void insertQuarter() {}

    @Override
    public void ejectQuarter() {}

    @Override
    public void turnCrank() {}

    @Override
    public void dispense() {
        if (tissueMachine.getCount() > 0) {
            tissueMachine.setCount(tissueMachine.getCount() - 1);
            tissueMachine.setState(tissueMachine.getNoQuarterState());
        } else {
            tissueMachine.setState(tissueMachine.getSoldOutState());
        }
    }
}

售卖类

public class SoldState implements State {
    private TissueMachine tissueMachine;

    @Override
    public void insertQuarter() {
        tissueMachine.setState(this);
    }

    @Override
    public void ejectQuarter() {}

    @Override
    public void turnCrank() {}

    @Override
    public void dispense() {}
}

纸巾自动售货机类

@Getter
@Setter
public class TissueMachine {//纸巾售货机类
    private State soldOutState, noQuarterState, hasQuarterState, soldState, state;
    int count = 0;//纸巾数

    public TissueMachine(int count) {
        this.count = count;
    }
}