状态模式(state pattern) 未使用状态模式详解

状态模式可以控制状态的转换, 未使用设计模式时, 程序会非常繁杂.

具体方法:

1. 状态转换类.

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

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

    final static int SOLD_OUT = 0;
    final static int NO_QUARTER = 1;
    final static int HAS_QUARTER = 2;
    final static int SOLD = 3;  

    int state = SOLD_OUT;
    int count = 0;  

    public GumballMachine(int count) {
        this.count = count;
        if (count > 0) {
            state = NO_QUARTER; //转换模式
        }
    }  

    public void insertQuarter() { //输入25分钱
        if (state == HAS_QUARTER) {
            System.out.println("You can't insert another quarter.");
        } else if (state == NO_QUARTER) {
            state = HAS_QUARTER;
            System.out.println("You inserted a quarter.");
        } else if (state == SOLD_OUT) {
            System.out.println("You can't insert a quarter, the machine is sold out.");
        } else if (state == SOLD) {
            System.out.println("Please wait, we're already giving you a gumball.");
        }
    }  

    public void ejectQuarter() { //退回25分钱
        if (state == HAS_QUARTER) {
            System.out.println("Quarter returned.");
            state = NO_QUARTER;
        } else if (state == NO_QUARTER) {
            System.out.println("You haven't inserted a quarter.");
        } else if (state == SOLD) {
            System.out.println("Sorry, you already turned the crank.");
        } else if (state == SOLD_OUT) {
            System.out.println("You can't eject, you haven't inserted a quarter yet.");
        }
    }  

    public void turnCrank() { //摇动转杆
        if (state == SOLD) {
            System.out.println("Turning twice doesn't get another gumball.");
        } else if (state == NO_QUARTER) {
            System.out.println("You turned but there's no quarter.");
        } else if (state == SOLD_OUT) {
            System.out.println("You turned, but there are no gumballs");
        } else if (state == HAS_QUARTER) {
            System.out.println("You turned...");
            state = SOLD;
            dispense();
        }
    }  

    public void dispense() {
        if (state == SOLD) {
            System.out.println("A gumball comes rolling out the slot.");
            count--;
            if (count == 0) {
                System.out.println("Opps, out of gumballs.");
                state = SOLD_OUT;
            } else {
                state = NO_QUARTER;
            }
        } else if (state == NO_QUARTER) {
            System.out.println("You need to pay first.");
        } else if (state == SOLD_OUT) {
            System.out.println("No gumball dispensed.");
        } else if (state == HAS_QUARTER) {
            System.out.println("No gumball dispensed.");
        }
    }  

    public void refill(int numGumballs) {
        this.count = numGumballs;
        state = NO_QUARTER;
    }  

    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 ");
        if (state == SOLD_OUT) {
            result.append("sold out.");
        } else if (state == NO_QUARTER) {
            result.append("waiting for quarter.");
        } else if (state == HAS_QUARTER) {
            result.append("waitring for turn of crank.");
        } else if (state == SOLD) {
            result.append("delivering a gumball.");
        }
        result.append("\n");
        return result.toString();
    }
}

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