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;
}
@Override
public void insertQuarter() {
System.out.println("You can't insert another quarter");
}
@Override
public void ejectQuarter() {
System.out.println("Quarter returned");
gumballMachine.setState(gumballMachine.getNoQuarterState());
}
@Override
public void turnCrank() {
System.out.println("You turned...");
gumballMachine.setState(gumballMachine.getSoldState());
}
@Override
public void dispense() {
System.out.println("No gumball dispensed");
}
}public class NoQuarterState implements State {
GumballMachine gumballMachine;
public NoQuarterState(GumballMachine gumballMachine) {
this.gumballMachine = gumballMachine;
}
@Override
public void insertQuarter() {
System.out.println("You insert a quarter");
gumballMachine.setState(gumballMachine.getHasQuarterState());
}
@Override
public void ejectQuarter() {
System.out.println("You haven't insert a quarter");
}
@Override
public void turnCrank() {
System.out.println("You turned, but there's no quarter");
}
@Override
public void dispense() {
System.out.println("You need to pay first");
}
}public class SoldOutState implements State {
GumballMachine gumballMachine;
public SoldOutState(GumballMachine gumballMachine) {
this.gumballMachine = gumballMachine;
}
@Override
public void insertQuarter() {
System.out.println("You can't insert a quarter, the machine is sold out");
}
@Override
public void ejectQuarter() {
System.out.println("You can't eject, you haven't inserted a quarter yet");
}
@Override
public void turnCrank() {
System.out.println("You turned, but there are no gumballs");
}
@Override
public void dispense() {
System.out.println("No gumball dispensed");
}
}public class SoldState implements State {
GumballMachine gumballMachine;
public SoldState(GumballMachine gumballMachine) {
this.gumballMachine = gumballMachine;
}
@Override
public void insertQuarter() {
System.out.println("Please wait, we're already giving you a gumball");
}
@Override
public void ejectQuarter() {
System.out.println("Sorry, you already turned the crank");
}
@Override
public void turnCrank() {
System.out.println("Turning twice doesn't get you another gumball!");
}
@Override
public 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 there's 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 haven't insert a quarter
You insert a quarter
You can't 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 can't insert a quarter, the machine is sold out
You turned, but there are no gumballs
No gumball dispensed
