网站开发强制开启浏览器极速模式,深圳专业网站建设价格,广州市建设监理协会网站,扬州网站建设文章状态模式通过改变对象内部的状态来帮助对象控制自己的行为。 这是一张状态图#xff0c;其中每个圆圈都是一个状态。
最简单#xff0c;第一反应的实现就是使用一个变量来控制状态值#xff0c;并在方法内书写条件代码来处理不同情况。
package headfirst.designpatterns.…状态模式通过改变对象内部的状态来帮助对象控制自己的行为。 这是一张状态图其中每个圆圈都是一个状态。
最简单第一反应的实现就是使用一个变量来控制状态值并在方法内书写条件代码来处理不同情况。
package headfirst.designpatterns.state.gumball;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;}}public void insertQuarter() {if (state HAS_QUARTER) {System.out.println(You cant 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 cant insert a quarter, the machine is sold out);} else if (state SOLD) {System.out.println(Please wait, were already giving you a gumball);}}public void ejectQuarter() {if (state HAS_QUARTER) {System.out.println(Quarter returned);state NO_QUARTER;} else if (state NO_QUARTER) {System.out.println(You havent 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 cant eject, you havent inserted a quarter yet);}}public void turnCrank() {if (state SOLD) {System.out.println(Turning twice doesnt get you another gumball!);} else if (state NO_QUARTER) {System.out.println(You turned but theres 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();}}private void dispense() {if (state SOLD) {System.out.println(A gumball comes rolling out the slot);count count - 1;if (count 0) {System.out.println(Oops, 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(waiting for turn of crank);} else if (state SOLD) {result.append(delivering a gumball);}result.append(\n);return result.toString();}
}
以上的代码最大的问题就是没有遵守开发-关闭原则一遇到新的需求投币后有10%的概率出现“赢家”状态给出2颗糖果就需要修改源代码重新整理所有代码的逻辑。
重构后的代码理念
定义一个State接口糖果机器的每个动作都在接口中有一个对应的方法。为机器中的每个状态实现一个状态类。这些类将负责在对应状态下进行机器的行为。将动作委托到状态类。 // 每种状态的各个方法的行为都不一样NoQuarterState
{insertQuarter() // 转到HasQuarterStateejectQuarter() // 未投入25分钱turnCrank() // 未投入25分钱转动曲柄无效dispense() // 未投入25分钱不能分发糖果
}
在新的糖果机中我们不使用静态整数而使用state对象。
public class GumballMachine {// 所有的状态对象都在构造器中创建并赋值State soldOutState;State noQuarterState;State hasQuarterState;State soldState;State state;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 numberGumballs;if (numberGumballs 0) {state noQuarterState;} else {state soldOutState;}}public void insertQuarter() {state.insertQuarter();}public void ejectQuarter() {state.ejectQuarter();}public void turnCrank() {state.turnCrank();state.dispense();}void releaseBall() {System.out.println(A gumball comes rolling out the slot...);if (count 0) {count count - 1;}}int getCount() {return count;}void refill(int count) {this.count count;System.out.println(The gumball machine was just refilled; its new count is: this.count);state.refill();}void setState(State state) {this.state state;}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 String toString() {StringBuffer result new StringBuffer();result.append(\nMighty Gumball, Inc.);result.append(\nJava-enabled Standing Gumball Model #2004);result.append(\nInventory: count gumball);if (count ! 1) {result.append(s);}result.append(\n);result.append(Machine is state \n);return result.toString();}
}
现在我们已经可以
将每个状态的行为局部化到它自己的类中。将容易产生问题的if语句删除以方便日后的维护。让每个状态“对修改关闭”让糖果机“对扩展开放”可以加入新的状态类
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。 策略模式和状态模式的类图是一样的回去翻了下书好像没瞅到但
我们把策略模式想成是除了继承之外的一种弹性替代方案。如果使用继承定义一个类的行为则会被这个行为困住很难修改。
状态模式是不用在context中放置许多条件判断的替代方案。通过将行为包装进状态对象中可以通过在context内简单改变状态对象来改变context的行为。 在GumballMachine中状态决定了下一个状态应该是什么。ConcreteState总是决定接下来的状态是什么吗
状态转换是固定的时候就适合放在Context中。转换是更动态的适合通常就会放在状态类中。 // GumballMachine的修改和WinnerState的实现是很简单的
// 这里就只将HasQuarterState列出import java.util.Random;public class HasQuarterState implements State {Random randomWinner new Random(System.currentTimeMillis());GumballMachine gumballMachine;public HasQuarterState(GumballMachine gumballMachine) {this.gumballMachine gumballMachine;}public void insertQuarter() {System.out.println(You cant insert another quarter);}public void ejectQuarter() {System.out.println(Quarter returned);gumballMachine.setState(gumballMachine.getNoQuarterState());}public void turnCrank() {System.out.println(You turned...);int winner randomWinner.nextInt(10);if ((winner 0) (gumballMachine.getCount() 1)) {gumballMachine.setState(gumballMachine.getWinnerState());} else {gumballMachine.setState(gumballMachine.getSoldState());}}public void dispense() {System.out.println(No gumball dispensed);}public void refill() { }public String toString() {return waiting for turn of crank;}
} ------------------
