设计模式之组合模式java实现

组合模式：允许你将对象组合成树形结构来表现 “整体/部分” 层次结构。组合能让客户以一致的方式处理个别对象以及对象组合。

案例情景：上次，我和友人去超市分头购物，在结帐时，我们遍历一下我们的 “扫货” 清单（遍历打印购物清单），在实现上，Me使用ArrayList，友人使用Thing[]数组，给遍历造成困扰。

在遍历时发现赠送的商品，没有打印。现在我们有打印赠送物品的需求。

AbstractThing.java

public abstract class AbstractThing {
public abstract String toString();
public void add(AbstractThing thing){};
public void remove(AbstractThing thing){};

}

Thing.java

import java.util.ArrayList;
import java.util.Iterator;

public class Thing extends AbstractThing{
private ArrayList<AbstractThing> list = new ArrayList<AbstractThing>();

private String name;
private long price;
public Thing(String name,long price){
this.name = name;
this.price = price;
}
@Override
public String toString() {
String returnString  = "Thing [name=" + name + ", price=" + price + "]";
for(Iterator<AbstractThing> iterator=list.iterator();iterator.hasNext();){
returnString +=iterator.next();
}
return returnString;
}
@Override
public void add(AbstractThing thing) {
list.add(thing);
}
@Override
public void remove(AbstractThing thing) {
list.remove(thing);
}

}

ThingItem.java

public class ThingItem extends AbstractThing{
private String name;
private long price;
public ThingItem(String name,long price){
this.name = name;
this.price = price;
}
@Override
public String toString() {
return "赠送 [name=" + name + ", price=" + price + "]";
}
}

ArrayIterator.java

import java.util.Iterator;

public class ArrayIterator implements Iterator<Thing>{
private Thing[] thingArray;
private int position = 0;
public ArrayIterator(Thing[] array){
thingArray = array;
}

@Override
public boolean hasNext() {
while(position<thingArray.length && thingArray[position] != null){
return true;
}
return false;
}

@Override
public Thing next() {
return thingArray[position++];
}

@Override
public void remove() {
//noting to do
}

}

Me.java

import java.util.ArrayList;
import java.util.Iterator;

public class Me {
private ArrayList<Thing> shopping = new ArrayList<Thing>();

public Me(){
shopping.add(new Thing("巧克力", 35));
shopping.add(new Thing("凉茶", 4));
shopping.add(new Thing("袜子", 9));
shopping.add(new Thing("香蕉", 12));
//买电脑送鼠标，耳机，键盘
Thing computer = new Thing("电脑", 3000);
computer.add(new ThingItem("鼠标", 0));
computer.add(new ThingItem("耳机", 0));
computer.add(new ThingItem("键盘", 0));

shopping.add(computer);

}

public Iterator<Thing> createIterator(){
return shopping.iterator();
}
}

Friends.java

import java.util.Iterator;

public class Friends {
private Thing[] shopping = new Thing[100];

public Friends(){
shopping[0] = new Thing("牛奶",15);
shopping[1] = new Thing("苹果",10);
shopping[2] = new Thing("薯片",4);

//买手机送蓝牙耳机
Thing phone = new Thing("手机", 2000);
ThingItem bluetoothHeadset = new ThingItem("蓝牙耳机", 0);
phone.add(bluetoothHeadset);

shopping[3] = phone;
}

public Iterator<Thing> createIterator(){
return new ArrayIterator(shopping);
}
}

Test.java

import java.security.AllPermission;
import java.util.ArrayList;
import java.util.Iterator;

public class Test {
public static void main(String args[]){
ArrayList<Iterator<Thing>> allIterator = new ArrayList<Iterator<Thing>>();
Me me = new Me();
Friends friends = new Friends();

Iterator<Thing> meIterator = me.createIterator();
Iterator<Thing> friendsIterator = friends.createIterator();
allIterator.add(meIterator);
allIterator.add(friendsIterator);

for(Iterator<Thing> iterator:allIterator){
while(iterator.hasNext()){
System.out.println(iterator.next());
}
System.out.println("---------------------");
}
}
}

测试结果：

Thing [name=巧克力, price=35]
Thing [name=凉茶, price=4]
Thing [name=袜子, price=9]
Thing [name=香蕉, price=12]
Thing [name=电脑, price=3000]赠送 [name=鼠标, price=0]赠送 [name=耳机, price=0]赠送 [name=键盘, price=0]
---------------------
Thing [name=牛奶, price=15]
Thing [name=苹果, price=10]
Thing [name=薯片, price=4]
Thing [name=手机, price=2000]赠送 [name=蓝牙耳机, price=0]
---------------------