设计模式-状态者模式

• 定义

允许一个对象在内部状态变化时改变它的行为，类似于改变类

• 结构
  • Context: 环境类
  • State: 抽象状态类
  • ConcreteState: 具体状态类

• 优点
  • 枚举可能的状态，在枚举状态之前需要确定状态种类。
  • 将所有与某个状态有关的行为放到一个类中，并且可以方便地增加新的状态，只需要改变对象状态即可改变对象的行为。
  • 允许状态转换逻辑与状态对象合成一体，而不是某一个巨大的条件语句块。
• 缺点
  • 状态模式的使用必然会增加系统类和对象的个数。
  • 状态模式的结构与实现都较为复杂，如果使用不当将导致程序结构和代码的混乱。
  • 状态模式对“开闭原则”的支持并不太好，对于可以切换状态的状态模式，增加新的状态类需要修改那些负责状态转换的源代码，否则无法切换到新增状态；而且修改某个状态类的行为也需修改对应类的源代码
• 代码

原始代码

package com.example.design.pattern.book.state;

public class BallMachine {

    final static int sold_out = 0;
    final static int no_quarter = 1;
    final static int has_quarter = 2;
    final static int sold = 3;

    int count = 0;
    int currentState = sold_out;

    public BallMachine(int count) {

        this.count = count;
        if (this.count > 0) {
            currentState = no_quarter;
        }
    }

    /**
     * 投入钱
     */
    public void insertQuarter() {

        if (currentState == has_quarter) {
            System.out.println("has quart");
        } else if (currentState == no_quarter) {
            currentState = has_quarter;
            System.out.println("you insert a quarter");
        } else if (currentState == sold_out) {
            System.out.println("can not insert a quarter , sold out");
        } else if (currentState == sold) {
            System.out.println("please wait ,a ball will come out");
        }
    }

    /**
     * 退回钱
     */
    public void ejectQuarter() {

        if (currentState == has_quarter) {
            System.out.println("quarter turn back");
            currentState = no_quarter;
        } else if (currentState == no_quarter) {
            System.out.println("no quarter");
        } else if (currentState == sold_out) {
            System.out.println("can not eject");
        } else if (currentState == sold) {
            System.out.println("can not eject");
        }
    }

    /**
     * 转动手柄
     */
    public void turnCrank() {
        if (currentState == has_quarter) {
            System.out.println("you turned ....");
            currentState = sold;
            dispense();
        } else if (currentState == no_quarter) {
            System.out.println("no quarter");
        } else if (currentState == sold_out) {
            System.out.println("can not turn");
        } else if (currentState == sold) {
            System.out.println("can not turn");
        }
    }

    private void dispense() {

        if (currentState == has_quarter) {
            System.out.println("no");
        } else if (currentState == no_quarter) {
            currentState = has_quarter;
            System.out.println("no");
        } else if (currentState == sold_out) {
            System.out.println("no");
        } else if (currentState == sold) {

            System.out.println("a ball come");

            count = count - 1;
            if (count == 0) {
                System.out.println("no ball");
                currentState = sold_out;
            } else {
                currentState = no_quarter;
            }
        }
    }


}

Test

 @org.junit.Test
    public void testxx(){
       BallMachine ballMachine = new BallMachine(1);

       ballMachine.insertQuarter();
        ballMachine.turnCrank();

使用状态模式后的代码

抽象状态类

package com.example.design.pattern.book.state.ok;

public interface AbState {
    final static int sold_out = 0;
    final static int no_quarter = 1;
    final static int has_quarter = 2;
    final static int sold = 3;

     void insertQuarter();

     void ejectQuarter();

     void turnCrank();

     void dispense();
}

各状态类

package com.example.design.pattern.book.state.ok;

public class HasQuarterState implements AbState {

    private BallMachine1 ballMachine1;

    public HasQuarterState(BallMachine1 ballMachine1) {
        this.ballMachine1 = ballMachine1;
    }

    @Override
    public void insertQuarter() {

        System.out.println("has quart");

    }

    @Override
    public void ejectQuarter() {

        System.out.println("quarter returned");
        ballMachine1.setCurrentState(ballMachine1.noQuarterState);
    }

    @Override
    public void turnCrank() {
        System.out.println("you turned");
        ballMachine1.setCurrentState(ballMachine1.soldState);
    }

    @Override
    public void dispense() {
        System.out.println("no ball dispense");
    }
}

package com.example.design.pattern.book.state.ok;

public class NoQuarterState implements AbState {
    private BallMachine1 ballMachine1;

    public NoQuarterState(BallMachine1 ballMachine1) {
        this.ballMachine1 = ballMachine1;
    }

    @Override
    public void insertQuarter() {
        System.out.println("insert a quarter");
        ballMachine1.setCurrentState(ballMachine1.hasQuarterState);
    }

    @Override
    public void ejectQuarter() {
        System.out.println("has no quarter");
    }

    @Override
    public void turnCrank() {

        System.out.println("no quarter");
    }

    @Override
    public void dispense() {

        System.out.println("no quarter");
    }
}

package com.example.design.pattern.book.state.ok;

public class SoldoutQuarterState implements AbState {


    private BallMachine1 ballMachine1;

    public SoldoutQuarterState(BallMachine1 ballMachine1) {
        this.ballMachine1 = ballMachine1;
    }

    @Override
    public void insertQuarter() {
//.....
    }

    @Override
    public void ejectQuarter() {
//.....

    }

    @Override
    public void turnCrank() {
//.....

    }

    @Override
    public void dispense() {
//.....

    }
}

package com.example.design.pattern.book.state.ok;

public class SoldState implements AbState {

    private BallMachine1 ballMachine1;

    public SoldState(BallMachine1 ballMachine1) {
        this.ballMachine1 = ballMachine1;
    }

    @Override
    public void insertQuarter() {
//.....

    }

    @Override
    public void ejectQuarter() {
//.....

    }

    @Override
    public void turnCrank() {
//.....

    }

    @Override
    public void dispense() {
//.....

    }
}

package com.example.design.pattern.book.state.ok;

import com.example.design.pattern.book.state.ok.*;

public class BallMachine1 {

    SoldState soldState;
    HasQuarterState hasQuarterState;
    NoQuarterState noQuarterState;
    SoldoutQuarterState soldoutQuarterState;

    int count = 0;
    AbState currentState = soldState;

    public BallMachine1(int count) {
        soldState = new SoldState(this);
        noQuarterState = new NoQuarterState(this);
        hasQuarterState = new HasQuarterState(this);
        soldoutQuarterState = new SoldoutQuarterState(this);

        this.count = count;

        if (this.count > 0) {
            currentState = noQuarterState;
        }
    }

    /**
     * 投入钱
     */
    public void insertQuarter() {

        currentState.insertQuarter();
    }

    /**
     * 退回钱
     */
    public void ejectQuarter() {

        currentState.ejectQuarter();

    }

    /**
     * 转动手柄
     */
    public void turnCrank() {
        currentState.turnCrank();
    }

    private void dispense() {

        currentState.dispense();

    }


    public void setCurrentState(AbState currentState) {
        this.currentState = currentState;
    }
}

        BallMachine1 ballMachine1 = new BallMachine1(1);

        ballMachine1.insertQuarter();
        ballMachine1.turnCrank();

运行后打印

insert a quarter
you turned