状态模式(state pattern) 详解

状态模式(state pattern): 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.

建立Context类, 包含多个具体状态(concrete state)类的组合, 根据状态的不同调用具体的方法, state.handle(), 包含set\get方法改变状态.

状态接口(state interface), 包含抽象方法handle(), 具体状态类(concrete state)继承(implement)状态类(state), 实现handle()方法;

具体方法:

1. Context类, 组合多个具体状态类(concrete state), 并提供set\get方法, 调用状态的方法(handle), 改变状态.

/**
 * @time 2014年7月11日
 */
package state.pattern;  

/**
 * @author C.L.Wang
 *
 */
public class GumballMachine {  

    State soldOutState;
    State noQuarterState;
    State hasQuarterState;
    State soldState;
    State winnerState;  

    State state = soldOutState;
    int count = 0;  

    /**
     *
     */
    public GumballMachine(int numberGumballs) {
        // TODO Auto-generated constructor stub
        soldOutState = new SoldOutState(this);
        noQuarterState = new NoQuarterState(this);
        hasQuarterState = new HasQuarterState(this);
        soldState = new SoldState(this);
        winnerState = new WinnerState(this);  

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

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

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

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

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

    void releaseBall() {
        System.out.println("A gumball comes rolling out the slot...");
        if (count != 0)
            count --;
    }  

    int getCount() {
        return count;
    }  

    void refill(int count) {
        this.count = count;
        state = noQuarterState;
    }  

    public State getState() {
        return state;
    }  

    public State getSoldOutState() {
        return soldOutState;
    }  

    public State getNoQuarterState() {
        return noQuarterState;
    }  

    public State getHasQuarterState() {
        return hasQuarterState;
    }  

    public State getSoldState() {
        return soldState;
    }  

    public State getWinnerState() {
        return winnerState;
    }  

    public String toString() {
        StringBuffer result = new StringBuffer();
        result.append("\nMighty Gumball, Inc.");
        result.append("\nJava-enabled Standing Gumball Model #2004\n");
        result.append("Inventory: " + count + " gumball");
        if (count != 1) {
            result.append("s");
        }
        result.append("\nMachine is " + state + "\n");
        return result.toString();
    }
}

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