design pattern——状态模式
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针对问题：有时候一个方法可能有很多if..else来判断状态后再执行相关操作，当很多方法都重复的出现这样的if..else判断时，就可以考虑用状态模式了。
? ? ? 状态模式的结构图和策略模式一样，事实上状态模式和策略很相似，不同的是状态模式除了委托状态外，状态实体自身持有主实体对象的引用，在状态实体内部可以动态的改变主实体的状态。
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状态模式结构图：
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状态模式实现代码：
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/** * 状态接口 * @author bruce * */public interface State {public void insertQuarter();public void ejectQuarter();public void turnCrank();public void dispense();}/** * 有钱状态 * @author bruce * */public class HasQuarterState implements State{GumballMachine gumballMachine;public HasQuarterState(GumballMachine gumballMachine){this.gumballMachine=gumballMachine;}public void dispense() {// TODO Auto-generated method stubSystem.out.println("No gumball dispensed");}public void ejectQuarter() {// TODO Auto-generated method stubSystem.out.println("Quarter returned");gumballMachine.setState(gumballMachine.getNoQuarterState());}public void insertQuarter() {// TODO Auto-generated method stubSystem.out.println("You can't insert another quarter");}public void turnCrank() {// TODO Auto-generated method stubSystem.out.println("You returned...");gumballMachine.setState(gumballMachine.getSoldState());}}/** * 没钱状态 * @author bruce * */public class NoQuarterState implements State{private GumballMachine gumballMachine;public NoQuarterState(GumballMachine gumballMachine){this.gumballMachine=gumballMachine;}public void dispense() {// TODO Auto-generated method stubSystem.out.println("You need to pay first");}public void ejectQuarter() {// TODO Auto-generated method stubSystem.out.println("You haven't inserted a quarter");}public void insertQuarter() {// TODO Auto-generated method stubSystem.out.println("You inserted a quarter");gumballMachine.setState(gumballMachine.getHasQuarterState());}public void turnCrank() {// TODO Auto-generated method stubSystem.out.println("You turned,but there's no quarter");}}/** * 售出状态 * @author bruce * */public class SoldState implements State{private GumballMachine gumballMachine;public SoldState(GumballMachine gumballMachine){this.gumballMachine=gumballMachine;}public void dispense() {// TODO Auto-generated method stubgumballMachine.releaseBall();if(gumballMachine.getCount()>0){gumballMachine.setState(gumballMachine.getNoQuarterState());}else{System.out.println("Oops,out of gumballs!");gumballMachine.setState(gumballMachine.getSoldOutState());}}public void ejectQuarter() {// TODO Auto-generated method stubSystem.out.println("Sorry, you already turned the crank");}public void insertQuarter() {// TODO Auto-generated method stubSystem.out.println("Please wait, we're already giving you a gumball");}public void turnCrank() {// TODO Auto-generated method stubSystem.out.println("Turning twice doesn't get you another gumball!");}}/** * 卖完状态 * @author bruce * */public class SoldOutState implements State{@SuppressWarnings("unused")private GumballMachine gumballMachine;public SoldOutState(GumballMachine gumballMachine){this.gumballMachine=gumballMachine;}public void dispense() {// TODO Auto-generated method stubSystem.out.println("No gumball dispensed");}public void ejectQuarter() {// TODO Auto-generated method stubSystem.out.println("You can't eject, you haven't inserted a quarter yet");}public void insertQuarter() {// TODO Auto-generated method stubSystem.out.println("You can't insert a quarter,the machine is sold out");}public void turnCrank() {// TODO Auto-generated method stubSystem.out.println("You turned, but there are no gumballs");}}/** * 糖果机 * @author bruce * */public class GumballMachine {State soldOutState;State noQuarterState;State hasQuarterState;State soldState;State state=soldOutState;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;}}public void insertQuarter(){state.insertQuarter();}public void ejectQuarter(){state.ejectQuarter();}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=count-1;}}public State getSoldOutState() {return soldOutState;}public State getNoQuarterState() {return noQuarterState;}public State getHasQuarterState() {return hasQuarterState;}public State getSoldState() {return soldState;}public State getState() {return state;}public int getCount() {return count;}}/** * 测试 * @author bruce * */public class Client {public static void main(String[] args) {GumballMachine gumballMachine=new GumballMachine(5);System.out.println("-------------");gumballMachine.insertQuarter();gumballMachine.turnCrank();System.out.println("-------------");gumballMachine.insertQuarter();gumballMachine.turnCrank();gumballMachine.insertQuarter();gumballMachine.turnCrank();System.out.println("-------------");/** * output: * -------------You inserted a quarterYou returned...A gumball comes rolling out the slot...-------------You inserted a quarterYou returned...A gumball comes rolling out the slot...You inserted a quarterYou returned...A gumball comes rolling out the slot...------------- */}}?