這個模式花費了挺長時間,開始有點難理解,其實就是
定義:動態給一個對象添加一些額外的職責,就象在牆上刷油漆.使用Decorator模式相比用生成子類方式達到功能的擴充顯得更爲靈活。
設計初衷:通常可以使用繼承來實現功能的拓展,如果這些需要拓展的功能的種類很繁多,那麼勢必生成很多子類,增加系統的複雜性,同時,使用繼承實現功能拓展,我們必須可預見這些拓展功能,這些功能是編譯時就確定了,是靜態的。
要點:裝飾者與被裝飾者擁有共同的超類,繼承的目的是繼承類型,而不是行爲
實際上Java 的I/O API就是使用Decorator實現的。
- //定義被裝飾者
- public interface Human {
- public void wearClothes();
- public void walkToWhere();
- }
- //定義裝飾者
- public abstract class Decorator implements Human {
- private Human human;
- public Decorator(Human human) {
- this.human = human;
- }
- public void wearClothes() {
- human.wearClothes();
- }
- public void walkToWhere() {
- human.walkToWhere();
- }
- }
- //下面定義三種裝飾,這是第一個,第二個第三個功能依次細化,即裝飾者的功能越來越多
- public class Decorator_zero extends Decorator {
- public Decorator_zero(Human human) {
- super(human);
- }
- public void goHome() {
- System.out.println("進房子。。");
- }
- public void findMap() {
- System.out.println("書房找找Map。。");
- }
- @Override
- public void wearClothes() {
- // TODO Auto-generated method stub
- super.wearClothes();
- goHome();
- }
- @Override
- public void walkToWhere() {
- // TODO Auto-generated method stub
- super.walkToWhere();
- findMap();
- }
- }
- public class Decorator_first extends Decorator {
- public Decorator_first(Human human) {
- super(human);
- }
- public void goClothespress() {
- System.out.println("去衣櫃找找看。。");
- }
- public void findPlaceOnMap() {
- System.out.println("在Map上找找。。");
- }
- @Override
- public void wearClothes() {
- // TODO Auto-generated method stub
- super.wearClothes();
- goClothespress();
- }
- @Override
- public void walkToWhere() {
- // TODO Auto-generated method stub
- super.walkToWhere();
- findPlaceOnMap();
- }
- }
- public class Decorator_two extends Decorator {
- public Decorator_two(Human human) {
- super(human);
- }
- public void findClothes() {
- System.out.println("找到一件D&G。。");
- }
- public void findTheTarget() {
- System.out.println("在Map上找到神祕花園和城堡。。");
- }
- @Override
- public void wearClothes() {
- // TODO Auto-generated method stub
- super.wearClothes();
- findClothes();
- }
- @Override
- public void walkToWhere() {
- // TODO Auto-generated method stub
- super.walkToWhere();
- findTheTarget();
- }
- }
- //定義被裝飾者,被裝飾者初始狀態有些自己的裝飾
- public class Person implements Human {
- @Override
- public void wearClothes() {
- // TODO Auto-generated method stub
- System.out.println("穿什麼呢。。");
- }
- @Override
- public void walkToWhere() {
- // TODO Auto-generated method stub
- System.out.println("去哪裏呢。。");
- }
- }
- //測試類,看一下你就會發現,跟java的I/O操作有多麼相似
- public class Test {
- public static void main(String[] args) {
- Human person = new Person();
- Decorator decorator = new Decorator_two(new Decorator_first(
- new Decorator_zero(person)));
- decorator.wearClothes();
- decorator.walkToWhere();
- }
- }
//定義被裝飾者
public interface Human {
public void wearClothes();
public void walkToWhere();
}
//定義裝飾者
public abstract class Decorator implements Human {
private Human human;
public Decorator(Human human) {
this.human = human;
}
public void wearClothes() {
human.wearClothes();
}
public void walkToWhere() {
human.walkToWhere();
}
}
//下面定義三種裝飾,這是第一個,第二個第三個功能依次細化,即裝飾者的功能越來越多
public class Decorator_zero extends Decorator {
public Decorator_zero(Human human) {
super(human);
}
public void goHome() {
System.out.println("進房子。。");
}
public void findMap() {
System.out.println("書房找找Map。。");
}
@Override
public void wearClothes() {
// TODO Auto-generated method stub
super.wearClothes();
goHome();
}
@Override
public void walkToWhere() {
// TODO Auto-generated method stub
super.walkToWhere();
findMap();
}
}
public class Decorator_first extends Decorator {
public Decorator_first(Human human) {
super(human);
}
public void goClothespress() {
System.out.println("去衣櫃找找看。。");
}
public void findPlaceOnMap() {
System.out.println("在Map上找找。。");
}
@Override
public void wearClothes() {
// TODO Auto-generated method stub
super.wearClothes();
goClothespress();
}
@Override
public void walkToWhere() {
// TODO Auto-generated method stub
super.walkToWhere();
findPlaceOnMap();
}
}
public class Decorator_two extends Decorator {
public Decorator_two(Human human) {
super(human);
}
public void findClothes() {
System.out.println("找到一件D&G。。");
}
public void findTheTarget() {
System.out.println("在Map上找到神祕花園和城堡。。");
}
@Override
public void wearClothes() {
// TODO Auto-generated method stub
super.wearClothes();
findClothes();
}
@Override
public void walkToWhere() {
// TODO Auto-generated method stub
super.walkToWhere();
findTheTarget();
}
}
//定義被裝飾者,被裝飾者初始狀態有些自己的裝飾
public class Person implements Human {
@Override
public void wearClothes() {
// TODO Auto-generated method stub
System.out.println("穿什麼呢。。");
}
@Override
public void walkToWhere() {
// TODO Auto-generated method stub
System.out.println("去哪裏呢。。");
}
}
//測試類,看一下你就會發現,跟java的I/O操作有多麼相似
public class Test {
public static void main(String[] args) {
Human person = new Person();
Decorator decorator = new Decorator_two(new Decorator_first(
new Decorator_zero(person)));
decorator.wearClothes();
decorator.walkToWhere();
}
}
運行結果:
其實就是進房子找衣服,然後找地圖這樣一個過程,通過裝飾者的三層裝飾,把細節變得豐富。
關鍵點:
1、Decorator抽象類中,持有Human接口,方法全部委託給該接口調用,目的是交給該接口的實現類即子類進行調用。
2、Decorator抽象類的子類(具體裝飾者),裏面都有一個構造方法調用super(human),這一句就體現了抽象類依賴於子類實現即抽象依賴於實現的原則。因爲構造裏面參數都是Human接口,只要是該Human的實現類都可以傳遞進去,即表現出Decorator dt = new Decorator_second(new Decorator_first(new Decorator_zero(human)));這種結構的樣子。所以當調用dt.wearClothes();dt.walkToWhere()的時候,又因爲每個具體裝飾者類中,都先調用super.wearClothes和super.walkToWhere()方法,而該super已經由構造傳遞並指向了具體的某一個裝飾者類(這個可以根據需要調換順序),那麼調用的即爲裝飾類的方法,然後才調用自身的裝飾方法,即表現出一種裝飾、鏈式的類似於過濾的行爲。
3、具體被裝飾者類,可以定義初始的狀態或者初始的自己的裝飾,後面的裝飾行爲都在此基礎上一步一步進行點綴、裝飾。
4、裝飾者模式的設計原則爲:對擴展開放、對修改關閉,這句話體現在我如果想擴展被裝飾者類的行爲,無須修改裝飾者抽象類,只需繼承裝飾者抽象類,實現額外的一些裝飾或者叫行爲即可對被裝飾者進行包裝。所以:擴展體現在繼承、修改體現在子類中,而不是具體的抽象類,這充分體現了依賴倒置原則,這是自己理解的裝飾者模式。
說的不清楚,有些只可意會不可言傳的感覺,多看幾遍代碼,然後自己敲出來運行一下,基本上就領悟了。
下面這個例子也有助於理解 裝飾的流程和作用
現在需要一個漢堡,主體是雞腿堡,可以選擇添加生菜、醬、辣椒等等許多其他的配料,這種情況下就可以使用裝飾者模式。
漢堡基類(被裝飾者,相當於上面的Human)
- package decorator;
- public abstract class Humburger {
- protected String name ;
- public String getName(){
- return name;
- }
- public abstract double getPrice();
- }
package decorator;
public abstract class Humburger {
protected String name ;
public String getName(){
return name;
}
public abstract double getPrice();
}
雞腿堡類(被裝飾者的初始狀態,有些自己的簡單裝飾,相當於上面的Person)- package decorator;
- public class ChickenBurger extends Humburger {
- public ChickenBurger(){
- name = "雞腿堡";
- }
- @Override
- public double getPrice() {
- return 10;
- }
- }
package decorator;
public class ChickenBurger extends Humburger {
public ChickenBurger(){
name = "雞腿堡";
}
@Override
public double getPrice() {
return 10;
}
}
配料的基類(裝飾者,用來對漢堡進行多層裝飾,每層裝飾增加一些配料,相當於上面Decorator)
- package decorator;
- public abstract class Condiment extends Humburger {
- public abstract String getName();
- }
package decorator;
public abstract class Condiment extends Humburger {
public abstract String getName();
}
生菜(裝飾者的第一層,相當於上面的decorator_zero)
- package decorator;
- public class Lettuce extends Condiment {
- Humburger humburger;
- public Lettuce(Humburger humburger){
- this.humburger = humburger;
- }
- @Override
- public String getName() {
- return humburger.getName()+" 加生菜";
- }
- @Override
- public double getPrice() {
- return humburger.getPrice()+1.5;
- }
- }
package decorator;
public class Lettuce extends Condiment {
Humburger humburger;
public Lettuce(Humburger humburger){
this.humburger = humburger;
}
@Override
public String getName() {
return humburger.getName()+" 加生菜";
}
@Override
public double getPrice() {
return humburger.getPrice()+1.5;
}
}
辣椒(裝飾者的第二層,相當於上面的decorator_first)
- package decorator;
- public class Chilli extends Condiment {
- Humburger humburger;
- public Chilli(Humburger humburger){
- this.humburger = humburger;
- }
- @Override
- public String getName() {
- return humburger.getName()+" 加辣椒";
- }
- @Override
- public double getPrice() {
- return humburger.getPrice(); //辣椒是免費的哦
- }
- }
package decorator;
public class Chilli extends Condiment {
Humburger humburger;
public Chilli(Humburger humburger){
this.humburger = humburger;
}
@Override
public String getName() {
return humburger.getName()+" 加辣椒";
}
@Override
public double getPrice() {
return humburger.getPrice(); //辣椒是免費的哦
}
}
測試類
- package decorator;
- public class Test {
- /**
- * @param args
- */
- public static void main(String[] args) {
- Humburger humburger = new ChickenBurger();
- System.out.println(humburger.getName()+" 價錢:"+humburger.getPrice());
- Lettuce lettuce = new Lettuce(humburger);
- System.out.println(lettuce.getName()+" 價錢:"+lettuce.getPrice());
- Chilli chilli = new Chilli(humburger);
- System.out.println(chilli.getName()+" 價錢:"+chilli.getPrice());
- Chilli chilli2 = new Chilli(lettuce);
- System.out.println(chilli2.getName()+" 價錢:"+chilli2.getPrice());
- }
- }
package decorator;
public class Test {
/**
* @param args
*/
public static void main(String[] args) {
Humburger humburger = new ChickenBurger();
System.out.println(humburger.getName()+" 價錢:"+humburger.getPrice());
Lettuce lettuce = new Lettuce(humburger);
System.out.println(lettuce.getName()+" 價錢:"+lettuce.getPrice());
Chilli chilli = new Chilli(humburger);
System.out.println(chilli.getName()+" 價錢:"+chilli.getPrice());
Chilli chilli2 = new Chilli(lettuce);
System.out.println(chilli2.getName()+" 價錢:"+chilli2.getPrice());
}
}
輸出
- 雞腿堡 價錢:10.0
- 雞腿堡 加生菜 價錢:11.5
- 雞腿堡 加辣椒 價錢:10.0
- 雞腿堡 加生菜 加辣椒 價錢:11.5
雞腿堡 價錢:10.0
雞腿堡 加生菜 價錢:11.5
雞腿堡 加辣椒 價錢:10.0
雞腿堡 加生菜 加辣椒 價錢:11.5
作者:jason0539
微博:http://weibo.com/2553717707
博客:http://blog.csdn.net/jason0539(轉載請說明出處)