一个问题引发的OOA&OOD讨论.

ooa(面向对象分析 analysis):
    要干什么？
ood(面向对象设计 design):
    怎么做？

面向对象的三大特称：封装，继承，多态。

模拟一下情形：
    小孩在睡觉
    醒来要求我喂他吃东西

先抽象出有哪些类，在确定每个类有哪些属性（变量而非方法）。
    利用要求中有哪些名词来确定（其中的名词可能是类也可能是属性）。

用设计模式，会使复杂度增加，开发成本增加，维护成本降低。

第一种方法（Dad主动监测Child是否醒来，比较耗费资源）：

class Child implements Runnable{
    private boolean wakenUp = false;
    
    void wakeUp(){
        wakenUp = true;
    }

    public boolean isWakenUp() {
        return wakenUp;
    }

    public void setWakenUp(boolean wakenUp) {
        this.wakenUp = wakenUp;
    }


    public void run() {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        this.wakeUp();
    }
}

class Dad implements Runnable{
    Child c;
    
    public Dad(Child c){
        this.c = c;
    }
    
    public void run(){
        while(!c.isWakenUp()){
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        feed(c);
    }

    private void feed(Child c2) {
        System.out.println("feed child!");
    }
}

public class Test {
    public static void main(String args[]){
        Child d = new Child();
        new Thread(d).start();
        new Thread(new Dad(d)).start();
    }
}

第二种方法（Dad不主动监测，Child醒来后调用，不具备可扩扩展，没有弹性）：

class Child implements Runnable{
    private boolean wakenUp = false;
    private Dad d;
    
    void wakeUp(){
        wakenUp = true;
        d.feed(this);
    }
    
    public Child(Dad d){
        this.d=d;
    }

    public void run() {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        this.wakeUp();
    }
}

class Dad{
    public void feed(Child c2) {
        System.out.println("feed child!");
    }
}

public class Test {
    public static void main(String args[]){
        Dad d = new Dad();
        Child c = new Child(d);
        new Thread(c).start();
    }
}

对于Child醒来会有不同的情况（如在哪里醒，什么时候醒，不同时候喂不同的东西），将这些信息告诉Dad。
第三种方法（将小孩醒来的情况封装为一个事件类）：

class WakenUpEvent{
    private long time;
    private String loc;
    private Child source;
    
    public long getTime() {
        return time;
    }
    public void setTime(long time) {
        this.time = time;
    }
    public String getLoc() {
        return loc;
    }
    public void setLoc(String loc) {
        this.loc = loc;
    }
    public Child getSource() {
        return source;
    }
    public void setSource(Child source) {
        this.source = source;
    }
    public WakenUpEvent(long time, String loc, Child source) {
        super();
        this.time = time;
        this.loc = loc;
        this.source = source;
    }
}

class Child implements Runnable{
    private Dad d;
    
    void wakeUp(){
        d.ActionToWakenUp(new WakenUpEvent(System.currentTimeMillis(),"bed",this));
    }
    
    public Child(Dad d){
        this.d=d;
    }

    public void run() {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        this.wakeUp();
    }
}

class Dad{
    public void ActionToWakenUp(WakenUpEvent wakenUpEvent) {
        System.out.println("feed child!");
    }
}

public class Test {
    public static void main(String args[]){
        Dad d = new Dad();
        Child c = new Child(d);
        new Thread(c).start();
    }
}

第四种方法（醒来之后，爷爷、奶奶、叔叔等也要做出反应）：

import java.util.ArrayList;
import java.util.List;

class WakenUpEvent{
    private long time;
    private String loc;
    private Child source;
    
    public long getTime() {
        return time;
    }
    public void setTime(long time) {
        this.time = time;
    }
    public String getLoc() {
        return loc;
    }
    public void setLoc(String loc) {
        this.loc = loc;
    }
    public Child getSource() {
        return source;
    }
    public void setSource(Child source) {
        this.source = source;
    }
    public WakenUpEvent(long time, String loc, Child source) {
        super();
        this.time = time;
        this.loc = loc;
        this.source = source;
    }
}

class Child implements Runnable{
    private List<WakenUpListener> wakenUpListeners=new ArrayList<WakenUpListener>();
    public void addWakenUpListener(WakenUpListener l){
        wakenUpListeners.add(l);
    }
    
    void wakeUp(){
        for(int i=0;i<wakenUpListeners.size();i++){
            WakenUpListener l = wakenUpListeners.get(i);
            l.ActionToWakenUp(new WakenUpEvent(System.currentTimeMillis(),"bed",this));
        }
    }

    public void run() {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        this.wakeUp();
    }
}

class Dad implements WakenUpListener{
    public void ActionToWakenUp(WakenUpEvent wakenUpEvent) {
        System.out.println("feed child!");
    }
}

class GrandFather implements WakenUpListener{
    public void ActionToWakenUp(WakenUpEvent wakenUpEvent) {
        System.out.println("hug child!");
    }
}

interface WakenUpListener{
    public void ActionToWakenUp(WakenUpEvent wakenUpEvent);
}

public class Test {
    public static void main(String args[]){
        Dad d = new Dad();
        Child c = new Child();
        GrandFather gf = new GrandFather();
        c.addWakenUpListener(d);
        c.addWakenUpListener(gf);
        new Thread(c).start();
    }
}

除了WakenUpEvent,还可以有哭事件等等，类似的定义事件接口。

项目中的class编译好之后会放到bin目录中，而bin默认设置在本项目中的classpath之下。
String类的方法为重点。

第四种方法（利用配置文件设置，使我们不用改main方法，只用增加类和改配置文件即可增加新的监听者）：

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;

class WakenUpEvent{
    private long time;
    private String loc;
    private Child source;
    
    public long getTime() {
        return time;
    }
    public void setTime(long time) {
        this.time = time;
    }
    public String getLoc() {
        return loc;
    }
    public void setLoc(String loc) {
        this.loc = loc;
    }
    public Child getSource() {
        return source;
    }
    public void setSource(Child source) {
        this.source = source;
    }
    public WakenUpEvent(long time, String loc, Child source) {
        super();
        this.time = time;
        this.loc = loc;
        this.source = source;
    }
}

class Child implements Runnable{
    private List<WakenUpListener> wakenUpListeners=new ArrayList<WakenUpListener>();
    public void addWakenUpListener(WakenUpListener l){
        wakenUpListeners.add(l);
    }
    
    void wakeUp(){
        for(int i=0;i<wakenUpListeners.size();i++){
            WakenUpListener l = wakenUpListeners.get(i);
            l.ActionToWakenUp(new WakenUpEvent(System.currentTimeMillis(),"bed",this));
        }
    }

    public void run() {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        this.wakeUp();
    }
}

class Dad implements WakenUpListener{
    public void ActionToWakenUp(WakenUpEvent wakenUpEvent) {
        System.out.println("feed child!");
    }
}

class GrandFather implements WakenUpListener{
    public void ActionToWakenUp(WakenUpEvent wakenUpEvent) {
        System.out.println("hug child!");
    }
}

interface WakenUpListener{
    public void ActionToWakenUp(WakenUpEvent wakenUpEvent);
}

public class Test {
    public static void main(String args[]){
        Child c = new Child();
        Properties props = new Properties();
        try {
            props.load(Test.class.getClassLoader().getResourceAsStream("observer.properties"));
        } catch (IOException e) {
            e.printStackTrace();
        }
        String[] observers = props.getProperty("observers").split(",");
        for(String s : observers){
            try {
                c.addWakenUpListener((WakenUpListener)Class.forName(s).newInstance());
            } catch (InstantiationException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
        }
        new Thread(c).start();
    }
}

----observer.properties----    //配置文件
observers=Dad,GrandFather

第五种方法（单例模式）：

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;

class WakenUpEvent{
    private long time;
    private String loc;
    private Child source;
    
    public long getTime() {
        return time;
    }
    public void setTime(long time) {
        this.time = time;
    }
    public String getLoc() {
        return loc;
    }
    public void setLoc(String loc) {
        this.loc = loc;
    }
    public Child getSource() {
        return source;
    }
    public void setSource(Child source) {
        this.source = source;
    }
    public WakenUpEvent(long time, String loc, Child source) {
        super();
        this.time = time;
        this.loc = loc;
        this.source = source;
    }
}

class Child implements Runnable{
    private List<WakenUpListener> wakenUpListeners=new ArrayList<WakenUpListener>();
    public void addWakenUpListener(WakenUpListener l){
        wakenUpListeners.add(l);
    }
    
    void wakeUp(){
        for(int i=0;i<wakenUpListeners.size();i++){
            WakenUpListener l = wakenUpListeners.get(i);
            l.ActionToWakenUp(new WakenUpEvent(System.currentTimeMillis(),"bed",this));
        }
    }

    public void run() {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        this.wakeUp();
    }
}

class Dad implements WakenUpListener{
    public void ActionToWakenUp(WakenUpEvent wakenUpEvent) {
        System.out.println("feed child!");
    }
}

class GrandFather implements WakenUpListener{
    public void ActionToWakenUp(WakenUpEvent wakenUpEvent) {
        System.out.println("hug child!");
    }
}

interface WakenUpListener{
    public void ActionToWakenUp(WakenUpEvent wakenUpEvent);
}

class PropertyMgr{
    private static Properties props = new Properties();
    
    static {
        try {
            props.load(Test.class.getClassLoader().getResourceAsStream("observer.properties"));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public static String getProperty(String key){
        return props.getProperty(key);
    }
}

public class Test {
    public static void main(String args[]){
        Child c = new Child();
        String[] observers = PropertyMgr.getProperty("observers").split(",");
        for(String s : observers){
            try {
                c.addWakenUpListener((WakenUpListener)Class.forName(s).newInstance());
            } catch (InstantiationException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
        }
        new Thread(c).start();
    }
}