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一. 前言
二. 实现 一. 前言 状态模式#xff08;State Pattern#xff09;#xff1a;它主要用来解决对象在多种状态转换时#xff0c;需要对外输出不同的行为的问题。状态和行为是一一对应的#xff0c;状态之间可以相互转换。当一个对象的内在状态改变时#x…目录
一. 前言
二. 实现 一. 前言 状态模式State Pattern它主要用来解决对象在多种状态转换时需要对外输出不同的行为的问题。状态和行为是一一对应的状态之间可以相互转换。当一个对象的内在状态改变时允许改变其行为这个对象看起来像是改变了其类。
状态模式和策略模式区别 1、策略模式封装了一组行为或者算法它允许Client在运行时动态的切换状态模式是帮助一个类在不同的状态下显示不同的行为依赖于内部的状态 2、策略模式不持有Context的引用而是被Context所使用状态模式的每个状态都持有Context的引用从而在Context中实现状态的转移 3、从理论上说策略模式定义对象应该“怎么做”状态模式定义了对象“是什么”“什么时候做”。 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。
二. 实现 Context 类为环境角色, 用于维护State 实例,这个实例定义当前状态聚合State。 State 是抽象状态角色,定义一个接口封装与Context 的一个特点接口相关行为。 ConcreteState 具体的状态角色每个子类实现一个与Context 的一个状态相关行为。
案例糖果销售机有多种状态每种状态下销售机有不同的行为状态可以发生转移使得销售机的行为也发生改变。 public interface State {/*** 投入 25 分钱*/void insertQuarter();/*** 退回 25 分钱*/void ejectQuarter();/*** 转动曲柄*/void turnCrank();/*** 发放糖果*/void dispense();
}
public class HasQuarterState implements State {private GumballMachine gumballMachine;public HasQuarterState(GumballMachine gumballMachine) {this.gumballMachine gumballMachine;}Overridepublic void insertQuarter() {System.out.println(You cant insert another quarter);}Overridepublic void ejectQuarter() {System.out.println(Quarter returned);gumballMachine.setState(gumballMachine.getNoQuarterState());}Overridepublic void turnCrank() {System.out.println(You turned...);gumballMachine.setState(gumballMachine.getSoldState());}Overridepublic void dispense() {System.out.println(No gumball dispensed);}
}
public class NoQuarterState implements State {GumballMachine gumballMachine;public NoQuarterState(GumballMachine gumballMachine) {this.gumballMachine gumballMachine;}Overridepublic void insertQuarter() {System.out.println(You insert a quarter);gumballMachine.setState(gumballMachine.getHasQuarterState());}Overridepublic void ejectQuarter() {System.out.println(You havent insert a quarter);}Overridepublic void turnCrank() {System.out.println(You turned, but theres no quarter);}Overridepublic void dispense() {System.out.println(You need to pay first);}
}
public class SoldOutState implements State {GumballMachine gumballMachine;public SoldOutState(GumballMachine gumballMachine) {this.gumballMachine gumballMachine;}Overridepublic void insertQuarter() {System.out.println(You cant insert a quarter, the machine is sold out);}Overridepublic void ejectQuarter() {System.out.println(You cant eject, you havent inserted a quarter yet);}Overridepublic void turnCrank() {System.out.println(You turned, but there are no gumballs);}Overridepublic void dispense() {System.out.println(No gumball dispensed);}
}
public class SoldState implements State {GumballMachine gumballMachine;public SoldState(GumballMachine gumballMachine) {this.gumballMachine gumballMachine;}Overridepublic void insertQuarter() {System.out.println(Please wait, were already giving you a gumball);}Overridepublic void ejectQuarter() {System.out.println(Sorry, you already turned the crank);}Overridepublic void turnCrank() {System.out.println(Turning twice doesnt get you another gumball!);}Overridepublic void dispense() {gumballMachine.releaseBall();if (gumballMachine.getCount() 0) {gumballMachine.setState(gumballMachine.getNoQuarterState());} else {System.out.println(Oops, out of gumballs);gumballMachine.setState(gumballMachine.getSoldOutState());}}
}
public class GumballMachine {private State soldOutState;private State noQuarterState;private State hasQuarterState;private State soldState;private State state;private int count 0;public GumballMachine(int numberGumballs) {count numberGumballs;soldOutState new SoldOutState(this);noQuarterState new NoQuarterState(this);hasQuarterState new HasQuarterState(this);soldState new SoldState(this);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();}public void setState(State state) {this.state state;}public void releaseBall() {System.out.println(A gumball comes rolling out the slot...);if (count ! 0) {count - 1;}}public State getSoldOutState() {return soldOutState;}public State getNoQuarterState() {return noQuarterState;}public State getHasQuarterState() {return hasQuarterState;}public State getSoldState() {return soldState;}public int getCount() {return count;}
}
public class Client {public static void main(String[] args) {GumballMachine gumballMachine new GumballMachine(5);gumballMachine.insertQuarter();gumballMachine.turnCrank();gumballMachine.insertQuarter();gumballMachine.ejectQuarter();gumballMachine.turnCrank();gumballMachine.insertQuarter();gumballMachine.turnCrank();gumballMachine.insertQuarter();gumballMachine.turnCrank();gumballMachine.ejectQuarter();gumballMachine.insertQuarter();gumballMachine.insertQuarter();gumballMachine.turnCrank();gumballMachine.insertQuarter();gumballMachine.turnCrank();gumballMachine.insertQuarter();gumballMachine.turnCrank();}
}
You insert a quarter
You turned...
A gumball comes rolling out the slot...
You insert a quarter
Quarter returned
You turned, but theres no quarter
You need to pay first
You insert a quarter
You turned...
A gumball comes rolling out the slot...
You insert a quarter
You turned...
A gumball comes rolling out the slot...
You havent insert a quarter
You insert a quarter
You cant insert another quarter
You turned...
A gumball comes rolling out the slot...
You insert a quarter
You turned...
A gumball comes rolling out the slot...
Oops, out of gumballs
You cant insert a quarter, the machine is sold out
You turned, but there are no gumballs
No gumball dispensed
