设计模式—状态模式【Head First 设计模式】

状态模式——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。
类图
关键代码展示
1.State接口

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

2.状态类

public class NoQuarterState implements State{
	GumballMachine GumballMachine;//糖果机的引用
	public NoQuarterState(GumballMachine gumballMachine){
		this.gumballMachine = gumballMachine;
	}
	public void insertQuarter(){
		System.out.println("You inserted a quarter");
		gumballMachine.setState(gumballMachine.getHasQuarterState());//进行了状态的转换
	}
	//其他方法
}

public class HasQuarterState implements State{
	GumballMachine gumballMachine;
	
	public HasQuarterState(GumballMachine gumballMachine){
		this.gumballMachine = gumballMachine;
	}
	public void ejectQuarter(){
		System.out.println("Quarter returned");
		gumballMachine.setState(gumballMachine.getNoQuarterState());
	}
	//其他方法
}
public class SoldOutState implements State{};
public class SoldState implements State{};

3.糖果机类

public class GumballMachine{
	State soldOutState;
	State noQuarterState;
	State hasQuarterState;
	State soldState;

	State state = soldOutState;
	int count = 0;

	public GumballMachine(int numberGumballs){
		soldOutState = new SoldOutState(this);
		noQuarterState = new NoQuarterState(this);
		hasQuarterState = new HasQuarterState(this);
		soldState = new SoldState(this);
		this.count = numberGunball;
		if(numberGumballs>0){
			state = noQuarterState;
		}
	}
	public void insertQuarter(){
		state.insertQuarter();
	}
	public void turnCrank(){
		state.turnCrank();
		state.dispense();
	}
	void setState(State state){
		this.state = state;
	}
	//其他方法
}

4.测试类

public class GumballMachineTest{
	public static void main(Stringp[] args){
		GumballMachine gumballMachine = new GumballMachine(5);
		System.out.println(gumballMachine);
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		System.out.println(gumballMachine);
	}
}

总结
1.状态模式允许一个对象基于内部状态而拥有不同的行为。
2.Context会将行为委托给当前的状态对象。
3.状态模式和策略模式有相同的类图，但是它们的意图不同：策略模式通常会用行为或算法来配置Context类。状态模式允许Context随着状态的改变而改变行为。
4.状态转换可以由State类或Context类控制。
如有错误欢迎评论指正
本文例子来自《Head First 设计模式》一书，若需要资源可以查看评论区

本文地址：https://blog.csdn.net/Aquaman_/article/details/109632625