一、状态模式概述
状态模式的定义: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。(对象行为型)
策略模式和状态模式是双胞胎,在出生时才分开。
- 策略模式是围绕可以互换的算法来创建成功业务的。
- 状态模式走的是更崇高的路,它通过改变对象内部的状态来帮助对象控制自己的行为。
- 状态模式的优缺点:
- 优点:
- 1.可以将不同的状态隔离;
- 2.每个状态都是一个单独的类;
- 3.可以将各种状态的转换逻辑 , 分布到状态的子类中 ,减少相互依赖;
- 4.增加新状态操作简单。
- 缺点:
- 如果状态数量比较多,状态类的数量会增加,业务场景系统变得很复杂;
- 如果业务中某个对象由几十上百个状态,就会很复杂,这时就需要对状态进行拆分处理。
- 优点:
- 适用场景:
- 一个对象存在多个状态,状态可以相互转换;
- 不同状态下,行为不同。
二、代码实现
状态模式主要包含三个角色:
- 环境(Context)角色:也称为上下文,它定义了客户感兴趣的接口,维护一个当前状态,并将与状态相关的操作委托给当前状态对象来处理;
- 抽象状态(State)角色:定义一个接口,用以封装环境对象中的特定状态所对应的行为;
- 具体状态(Concrete State)角色:实现抽象状态所对应的行为。
2.1 环境角色(GumballMachine)
package state.CandySolder;
//环境角色
public class GumballMachine {
private State noQuarterState;
private State hasQuarterState;
private State soldState;
private State soldOutState;
private State state = soldOutState; // 糖果机默认状态为售罄状态
int count = 0; // 糖果库存量
public GumballMachine(int numberGumballs) {
noQuarterState = new NoQuarterState(this);
hasQuarterState = new HasQuarterState(this);
soldState = new SoldState(this);
soldOutState = new SoldOutState(this);
count = numberGumballs;
if (numberGumballs > 0) {
state = noQuarterState; // 如果采购了糖果球(numberGumballs>0),则糖果机的状态为未投币状态
}
}
// 投入钱币
public void insertQuarter() {
state.insertQuarter();
}
// 退出钱币
public void ejectQuarter() {
state.ejectQuarter();
}
// 扭转曲柄
public void turnCrank() {
state.turnCrank();
state.dispense();
}
// 减少库存
public void releaseBall() {
if (count > 0) {
System.out.println("一个糖果球正在出库");
--count;
} else {
System.out.println("库存不足,一个糖果球无法出库");
}
}
// 设置状态
void setState(State state) {
this.state = state;
}
//get,set方法
public State getNoQuarterState() {
return noQuarterState;
}
public State getSoldOutState() {
return soldOutState;
}
public void setSoldOutState(State soldOutState) {
this.soldOutState = soldOutState;
}
public int getCount() {
return count;
}
public void setCount(int count) {
this.count = count;
}
public void setNoQuarterState(State noQuarterState) {
this.noQuarterState = noQuarterState;
}
public State getHasQuarterState() {
return hasQuarterState;
}
public void setHasQuarterState(State hasQuarterState) {
this.hasQuarterState = hasQuarterState;
}
public State getSoldState() {
return soldState;
}
public void setSoldState(State soldState) {
this.soldState = soldState;
}
}
2.2 抽象状态(State)
package state.CandySolder;
//抽象角色
public interface State {
void insertQuarter(); // 投入硬币操作
void ejectQuarter(); // 退出硬币操作
void turnCrank(); // 扭转曲柄操作
void dispense(); // 发放糖果操作
}
2.3 具体状态(HasQuarterState、NoQuarterState、SoldOutState、SoldState)
package state.CandySolder;
//具体状态,已经投放钱币状态
public class HasQuarterState implements State {
private GumballMachine gumballMachine;
public HasQuarterState(GumballMachine gumballMachine) {
this.gumballMachine = gumballMachine;
}
@Override
public void insertQuarter() {
// TODO Auto-generated method stub
System.out.println("您已经投入钱币!无须再次投入钱币!");
}
@Override
public void ejectQuarter() {
// TODO Auto-generated method stub
System.out.println("退款成功!");
gumballMachine.setState(gumballMachine.getNoQuarterState()); // 状态流转
}
@Override
public void turnCrank() {
// TODO Auto-generated method stub
System.out.println("正在出货中,请稍等");
gumballMachine.setState(gumballMachine.getSoldState()); // 状态流转
}
@Override
public void dispense() {
// TODO Auto-generated method stub
System.out.println("你还没有扭转曲柄,糖果不可以发放!");
}
}
package state.CandySolder;
//具体状态,没有投放钱币状态
public class NoQuarterState implements State {
private GumballMachine gumballMachine;
public NoQuarterState(GumballMachine gumballMachine) {
this.gumballMachine = gumballMachine;
}
@Override
public void insertQuarter() {
// TODO Auto-generated method stub
System.out.println("投入钱币成功!");
gumballMachine.setState(gumballMachine.getHasQuarterState()); // 状态流转
}
@Override
public void ejectQuarter() {
// TODO Auto-generated method stub
System.out.println("你还没有投入钱币,不能退回钱币!");
}
@Override
public void turnCrank() {
// TODO Auto-generated method stub
System.out.println("你还没有投入钱币,不能扭转曲柄!");
}
@Override
public void dispense() {
// TODO Auto-generated method stub
System.out.println("你还没有投入钱币,糖果不可以发放!");
}
}
package state.CandySolder;
//具体状态,糖果售空状态
public class SoldOutState implements State {
private GumballMachine gumballMachine;
public SoldOutState(GumballMachine gumballMachine) {
this.gumballMachine = gumballMachine;
}
@Override
public void insertQuarter() {
// TODO Auto-generated method stub
System.out.println("糖果已经售罄。不能投入钱币");
}
@Override
public void ejectQuarter() {
// TODO Auto-generated method stub
System.out.println("退回钱币成功!");
}
@Override
public void turnCrank() {
// TODO Auto-generated method stub
System.out.println("糖果已经售罄。不能扭转曲柄!");
}
@Override
public void dispense() {
// TODO Auto-generated method stub
System.out.println("糖果已经售罄。糖果无法出售!");
}
}
package state.CandySolder;
//具体状态,糖果售卖状态
public class SoldState implements State {
private GumballMachine gumballMachine;
public SoldState(GumballMachine gumballMachine) {
this.gumballMachine = gumballMachine;
}
@Override
public void insertQuarter() {
// TODO Auto-generated method stub
System.out.println("糖果正在出货中,请稍等。无须再次投入钱币!");
}
@Override
public void ejectQuarter() {
// TODO Auto-generated method stub
System.out.println("糖果正在出货中,请稍等。不能退回钱币!");
}
@Override
public void turnCrank() {
// TODO Auto-generated method stub
System.out.println("糖果正在出货中,请稍等。不需要再次扭转曲柄!");
}
@Override
public void dispense() {
// TODO Auto-generated method stub
if (gumballMachine.getCount() > 0) {
System.out.println("糖果正在出货中,请稍等!");
gumballMachine.releaseBall();
gumballMachine.setState(gumballMachine.getNoQuarterState()); // 状态流转
} else {
System.out.println("糖果库存不足,无法出货!");
gumballMachine.setState(gumballMachine.getSoldOutState()); // 状态流转
}
}
}
2.4 main方法实现状态模式
package state.CandySolder;
//测试
public class Test {
public static void main(String[] args) {
System.out.println("-----向糖果机中放入1枚糖果-----");
GumballMachine machine = new GumballMachine(1);
System.out.println("-----第一次购买糖果-----");
machine.insertQuarter();
machine.ejectQuarter();
machine.turnCrank();
System.out.println("-----第二次购买糖果-----");
machine.insertQuarter();
machine.turnCrank();
System.out.println("-----第三次购买糖果-----");
machine.insertQuarter();
machine.turnCrank();
machine.ejectQuarter();
}
}