状态模式

1. 定义

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。

2. 类图

3. Example

下面定义了一个State接口，接口里有个meaningOfLife的方法，定义了出生、三十、四十、五十、顿悟的几种状态。

人的主体PersonContext成员变量有State和感受（feeling）方法，测试代码中setAge来模拟人生阶段的变化，两次调用feeling略显不合理。。。

package com.gitlearning.hanldegit.patterns.state;


public interface State {
    void meaningOfLife(PersonContext personContext);
}

class Born implements State {

    @Override
    public void meaningOfLife(PersonContext personContext) {
        if (personContext.getAge() == 0) {

            System.out.println("Cry...");
        } else {
            personContext.setState(new Thirty());
        }
    }
}

class Thirty implements State {

    @Override
    public void meaningOfLife(PersonContext personContext) {
        if (personContext.getAge() <= 30) {

            System.out.println("三十而立");
        } else {
            personContext.setState(new Fourty());
        }
    }
}


class Fourty implements State {

    @Override
    public void meaningOfLife(PersonContext personContext) {
        if (personContext.getAge() <= 40) {
            System.out.println("四十而不惑");
        } else {
            personContext.setState(new Fifty());
        }
    }
}


class Fifty implements  State {

    @Override
    public void meaningOfLife(PersonContext personContext) {
        if (personContext.getAge() <= 50) {
            System.out.println("五十而知天命");
        } else {
            personContext.setState(new Hit());
        }
    }
}

class Hit implements State {

    @Override
    public void meaningOfLife(PersonContext personContext) {
        System.out.println("处世若大梦，胡为劳其生");
    }
}


package com.gitlearning.hanldegit.patterns.state;

import lombok.Data;

@Data
public class PersonContext {
    // 人生状态
    State state;
    int age;

    public void feeling() {
        state.meaningOfLife(this);
    }

    public void setAge(int age) {
        this.age = age;
        // 这里纯粹是为了改变一下状态
        feeling();
    }

    public PersonContext() {
        state = new Born();
    }
}


class Test {
    public static void main(String[] args) {
        PersonContext personContext = new PersonContext();
        personContext.feeling();
        personContext.setAge(30);
        personContext.feeling();
        personContext.setAge(40);
        personContext.feeling();
        personContext.setAge(50);
        personContext.feeling();
        personContext.setAge(60);
        personContext.feeling();
    }
}

输出：

Cry...
三十而立
四十而不惑
五十而知天命
处世若大梦，胡为劳其生