常用设计模式——状态模式

状态模式

概念

状态模式允许对象在内部状态改变时，改变它的行为。对象好像看起来修改了它的类。

这个模式将状态封装成了独立的类，并将动作委托到当前状态的对象。

• 状态模式用类代表不同的状态
• Context会将行为委托到当前对象
• 状态转换可以由State类控制或者Context控制
• 使用状态模式通常会导致程序中类的数目大大增加
• State可以被多个Context实例共享

策略模式区别

• 以状态模式而言，根据不同状态执行不同的行为，客户端对状态对象无需过多的了解。
• 对于策略对象而言，客户端通常要指定Context使用哪一个策略对象。

示例

代码语言：javascript复制

/**
 * 糖果机 状态接口
 * @author huangy on 2019-06-08
 */
public interface State {

    /**
     * 投币
     */
    void insertQuarter();

    /**
     * 退钱
     */
    void ejectQuarter();

    /**
     * 试着转动曲柄
     */
    void turnCrank();

    /**
     * 发放糖果
     */
    void dispense();
}

代码语言：javascript复制

/**
 * @author huangy on 2019-06-08
 */
public class HasQuarterState implements State {

    GumballMachine gumballMachine;

    public HasQuarterState(GumballMachine gumballMachine) {
        this.gumballMachine = gumballMachine;
    }

    @Override
    public void insertQuarter() {
        System.out.println("HasQuarterState insertQuarter");
    }

    @Override
    public void ejectQuarter() {
        System.out.println("HasQuarterState ejectQuarter");
    }

    @Override
    public void turnCrank() {
        System.out.println("HasQuarterState turnCrank");
        // 状态里面可以改变状态
        gumballMachine.setState(gumballMachine.soldState);
    }

    @Override
    public void dispense() {
        System.out.println("HasQuarterState dispense");
    }
}

代码语言：javascript复制

/**
 * @author huangy on 2019-06-08
 */
public class NoQuarterState implements State {

    GumballMachine gumballMachine;

    public NoQuarterState(GumballMachine gumballMachine) {
        this.gumballMachine = gumballMachine;
    }

    @Override
    public void insertQuarter() {
        System.out.println("NoQuarterState insertQuarter");
        gumballMachine.setState(gumballMachine.hasQuqrterState);
    }

    @Override
    public void ejectQuarter() {
        System.out.println("NoQuarterState ejectQuarter");
    }

    @Override
    public void turnCrank() {
        System.out.println("NoQuarterState turnCrank");
    }

    @Override
    public void dispense() {
        System.out.println("NoQuarterState dispense");
    }
}

代码语言：javascript复制

/**
 * @author huangy on 2019-06-08
 */
public class SoldOutState implements State {

    GumballMachine gumballMachine;

    public SoldOutState(GumballMachine gumballMachine) {
        this.gumballMachine = gumballMachine;
    }

    @Override
    public void insertQuarter() {
        System.out.println("SoldOutState insertQuarter");
    }

    @Override
    public void ejectQuarter() {
        System.out.println("SoldOutState ejectQuarter");
    }

    @Override
    public void turnCrank() {
        System.out.println("SoldOutState turnCrank");
    }

    @Override
    public void dispense() {
        System.out.println("SoldOutState dispense");
    }
}

代码语言：javascript复制

/**
 * @author huangy on 2019-06-08
 */
public class SoldState implements State {

    GumballMachine gumballMachine;

    public SoldState(GumballMachine gumballMachine) {
        this.gumballMachine = gumballMachine;
    }

    @Override
    public void insertQuarter() {
        System.out.println("SoldState insertQuarter");
    }

    @Override
    public void ejectQuarter() {
        System.out.println("SoldState ejectQuarter");
    }

    @Override
    public void turnCrank() {
        System.out.println("SoldState turnCrank");
    }

    @Override
    public void dispense() {
        System.out.println("SoldState dispense");
    }
}

代码语言：javascript复制

/**
 * 糖果机  （Context）
 * @author huangy on 2019-06-08
 */
public class GumballMachine {

    /**
     * 糖果机的状态
     */
    State soldOutState;

    State noQuqrterState;

    State hasQuqrterState;

    State soldState;

    // 当前状态
    State state = soldOutState;

    // 糖果数目
    int count = 0;

    public GumballMachine(int count) {
        this.count = count;
        soldOutState = new SoldOutState(this);
        noQuqrterState = new NoQuarterState(this);
        hasQuqrterState = new HasQuarterState(this);
        soldState = new SoldState(this);

        if (count > 0) {
            // Context里面可以改变状态
            state = noQuqrterState;
        }
    }

    public void insertQuarter() {
        state.insertQuarter();
    }

    public void ejectQuarter() {
        state.ejectQuarter();
    }

    public void turnCrank() {
        state.turnCrank();
        state.dispense();
    }

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

    public void releaseBall() {
        System.out.println("releaseBall");

        if (count != 0) {
            count--;
        }
    }

    @Override
    public String toString() {
        return "GumballMachine{"  
                "state="   state  
                ", count="   count  
                '}';
    }
}

代码语言：javascript复制

public class DemoTest {

    public static void main(String[] args) {
        GumballMachine gumballMachine = new GumballMachine(5);

        System.out.println(gumballMachine);

        gumballMachine.insertQuarter();
        gumballMachine.turnCrank();


        System.out.println(gumballMachine);
    }

}

state 客户端

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