状态模式

状态模式的定义：允许对象在内部状态改变时改变它的行为，对象看起来好像修改了它的类。将状态封装成为独立的类，并将动作委托到代表当前状态的对象。

状态接口：

public interface State {
    public void insertQuarter();
    
    public void ejectQuarter();
    
    public void turnCrank();
    
    public void dispense();
}

实现一个状态类：

public class NoQuarterState implements State {
    GumballMachine gumballMachine;//拥有状态的事物的引用
    
    public NoQuarterState(GumballMachine gumballMachine){
        this.gumballMachine = gumballMachine;
    }
    @Override
    public void insertQuarter() {
        System.out.println("You inserted a quarter!");
        gumballMachine.setState(gumballMachine.getHasQuarterState());
    }

    @Override
    public void ejectQuarter() {
        System.out.println("You haven't insert a quarter");
    }

    @Override
    public void turnCrank() {
        System.out.println("You turned, but there's no quarter");
    }

    @Override
    public void dispense() {
        System.out.println("You need to pay first");
    }

}

拥有状态的事物类：

public class GumballMachine {

    State  soldOutState;
    State noQuarterState;
    State hasQuarterState;
    State soldState;
    
    State state = soldOutState;
    int count=0;
    
    public GumballMachine(int numberGumballs){
        //构造方法的内容
    }
    
    void setState(State state){
        this.state = state;
    }
    
    public void insertQuarter(){
        state.insertQuarter();
    }
    
    public void ejectQuarter(){
        state.ejectQuarter();
    }
    
    public void turnCrank(){
        state.turnCrank();
    }
    
    public void releaseBall(){
        System.out.println("A gumball comes rolling out the slot ...");
        if(count != 0){
            count--;
        }
    }
}