java设计模式_状态模式

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一、什么是状态模式

State模式也叫状态模式，是行为设计模式的一种。State模式允许通过改变对象的内部状态而改变对象的行为，这个对象表现得就好像修改
了它的类一样。

二、状态模式的应用场景

状态模式主要解决的是当控制一个对象状态转换的条件表达式过于复杂时的情况。把状态的判断逻辑转译到表现不同状态的一系列类当中，可
以把复杂的判断逻辑简化。

三、状态模式的结构

四、状态模式的角色和职责
Context：用户对象拥有一个State类型的成员，以标识对象的当前状态； State：接口或基类
封装与Context的特定状态相关的行为； ConcreteState：接口实现类或子类实现了一个与Context某个状态相关的行为。

//示例1:public class Person {    private int hour;    public void setHour(int hour) {        this.hour = hour;    }    public int getHour() {        return hour;    }    public void doSomething()    {        if(hour == 7)        {            System.out.println("吃早餐");        } else if(hour == 12) {            System.out.println("吃中饭");        } else if(hour == 18) {            System.out.println("吃晚饭");        }    }}public class MainClass {    public static void main(String[] args) {        Person person = new Person();        person.setHour(7);        person.doSomething();        person.setHour(12);        person.doSomething();        person.setHour(18);        person.doSomething();    }}//吃早餐//吃中饭//吃晚饭////示例2:public abstract class State {    public abstract void  doSomething();}public  class MState extends State {    @Override    public void doSomething() {        System.out.println("吃早餐");    }}public  class LState extends State {    @Override    public void doSomething() {        System.out.println("吃中饭");    }}public  class SState extends State {    @Override    public void doSomething() {        System.out.println("吃晚饭");    }}public  class NoState extends State {    @Override    public void doSomething() {        System.out.println("未定义");    }}public class Person {    private int hour;    private State state;    public void setHour(int hour) {        this.hour = hour;    }    public int getHour() {        return hour;    }    public void doSomething()    {        if(hour == 7)        {            state = new MState();            state.doSomething();        } else if(hour == 12) {            state = new LState();            state.doSomething();        } else if(hour == 18) {            state = new SState();            state.doSomething();        } else {            state = new NoState();            state.doSomething();        }    }}public class MainClass {    public static void main(String[] args) {        Person person = new Person();        person.setHour(7);        person.doSomething();        person.setHour(12);        person.doSomething();        person.setHour(18);        person.doSomething();        person.setHour(8);        person.doSomething();    }}//吃早餐//吃中饭//吃晚饭//未定义//示例3:public abstract class State {    public abstract void  doSomething(Person person);}public  class MState extends State {    @Override    public void doSomething(Person person) {        if(person.getHour() == 7)            System.out.println("吃早餐");        else {            person.setState(new LState());            person.doSomething();        }    }}public  class LState extends State {    @Override    public void doSomething(Person person) {        if(person.getHour() == 12)            System.out.println("吃中饭");        else {            person.setState(new SState());            person.doSomething();        }    }}public  class SState extends State {    @Override    public void doSomething(Person person) {        if(person.getHour() == 18)            System.out.println("吃晚饭");        else {            person.setState(new NoState());            person.doSomething();        }    }}public  class NoState extends State {    @Override    public void doSomething(Person person) {        System.out.println("未定义");    }}public class Person {    private int hour;    private State state = new MState();    public void setState(State state) {        this.state = state;    }    public void setHour(int hour) {        this.hour = hour;    }    public int getHour() {        return hour;    }    public void doSomething()    {        state.doSomething(this);    }}public class MainClass {    public static void main(String[] args) {        Person person = new Person();        person.setHour(7);        person.doSomething();        person.setHour(12);        person.doSomething();        person.setHour(18);        person.doSomething();        person.setHour(8);        person.doSomething();    }}//吃早餐//吃中饭//吃晚饭//未定义

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