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状态模式，实时监测状态，当状态发生变化相应的也会进行一些更新。通过把各种状态转移逻辑分布到state的子类，来减少相互之间的依赖，可以消除庞大的条件分支语句。当一个对象的行为取决于它的状态，并且它必须在运行时刻根据状态改变它的行为时，就可以考虑使用状态模式了。

看看状态模式的UML类图：

基本逻辑代码

abstract class State{ public abstract void Handle(Context context);}

class ConcreteStateA extends State{ @Override public void Handle(Context context){   context.State = new ConcreteStateB(); }}

class ConcreteStateB extends State{ @Override public void Handle(Context context){   context.State = new ConcreteStateA(); }

class Context{ private State state; public Context(State state){  this.state = state; }  public State state{  return state; } public void setState(State s){   state = s; } public void                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              (){  state.Handle(this); }}

static void main(String[] args){ Context c = new Context(new ContextStateA()); c.Request(); c.Request();}

举个例子，一个人上班期间，根据时间的不同，对应不同的工作状态，那么按照平常的思路就是输入时间，一一去判断，这样的话就会违背了开放-封闭原则，这个时候采用状态模式，把每个时间点对应的状态，创建成为一个类，那么再添加类或者修改。都不会影响其他时间点的状态。

package com.abings.statemodel.StateModel;/** * Created by HaomingXu on 2016/9/12. */public abstract class State {    public abstract void workstate(Work work);}

package com.abings.statemodel.StateModel;import android.util.Log;/** * Created by HaomingXu on 2016/9/12. */public class AfternoonState extends State {    @Override    public void workstate(Work work) {        if (work.getHour() < 17){            Log.i("Tag","当前时间："+work.getHour()+"，下午工作，状态不错，继续努力。");        }else{            work.setState(new EveningState());            work.writeProgram();        }    }}

package com.abings.statemodel.StateModel;import android.util.Log;/** * Created by HaomingXu on 2016/9/12. */public class NoonState extends State {    @Override    public void workstate(Work work) {        if (work.getHour() < 14){            Log.i("Tag","当前时间："+work.getHour()+"，中午工作，饿了，犯困。");        }else{            work.setState(new AfternoonState());            work.writeProgram();        }    }}

package com.abings.statemodel.StateModel;import android.util.Log;/** * Created by HaomingXu on 2016/9/12. */public class ForenoonState extends State {    @Override    public void workstate(Work work) {        if (work.getHour() < 12){            Log.i("Tag","当前时间："+work.getHour()+"，上午工作，精神百倍。");        }else{            work.setState(new NoonState());            work.writeProgram();        }    }}

package com.abings.statemodel.StateModel;import android.util.Log;/** * Created by HaomingXu on 2016/9/12. */public class EveningState extends State {    @Override    public void workstate(Work work) {        if (work.isFinished()){            Log.i("Tag","当前时间："+work.getHour()+"，完成了。回家吧。");        }else{            if (work.getHour() < 21){                Log.i("Tag", "当前时间：" + work.getHour() + ",不行，没完成，继续加班。");            }else{                Log.i("Tag","当前时间："+work.getHour()+"，不行，没完成也要回家了。");            }        }    }}

package com.abings.statemodel.StateModel;/** * Created by HaomingXu on 2016/9/12. */public class Work {    private State state;    private int hour;    private boolean isFinished = false;    public boolean isFinished() {        return isFinished;    }    public void setIsFinished(boolean isFinished) {        this.isFinished = isFinished;    }    public int getHour() {        return hour;    }    public void setHour(int hour) {        this.hour = hour;    }    public Work(State state){        setState(state);    }    public State getState() {        return state;    }    public void setState(State state) {        this.state = state;    }    public void writeProgram(){        state.workstate(this);    }}

package com.abings.statemodel;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import com.abings.statemodel.StateModel.ForenoonState;import com.abings.statemodel.StateModel.Work;public class MainActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Work work = new Work(new ForenoonState());        //一天的工作        work.setHour(10);        work.writeProgram();        work.setHour(12);        work.writeProgram();        work.setHour(13);        work.writeProgram();        work.setHour(15);        work.writeProgram();        work.setHour(19);        work.writeProgram();        work.setHour(21);        work.setIsFinished(true);        work.writeProgram();    }}

09-12 15:28:19.201 20503-20503/? I/Tag: 当前时间：10，上午工作，精神百倍。09-12 15:28:19.201 20503-20503/? I/Tag: 当前时间：12，中午工作，饿了，犯困。09-12 15:28:19.201 20503-20503/? I/Tag: 当前时间：13，中午工作，饿了，犯困。09-12 15:28:19.202 20503-20503/? I/Tag: 当前时间：15，下午工作，状态不错，继续努力。09-12 15:28:19.202 20503-20503/? I/Tag: 当前时间：19,不行，没完成，继续加班。09-12 15:28:19.202 20503-20503/? I/Tag: 当前时间：21，完成了。回家吧。