多态及装饰者模式辨析

装饰者模式代码如下：

public class Coffee{
public void drink(){
System.out.println("drink coffee");
}
}

 

public abstract class CoffeeDecorator extends Coffee{
protected Coffee coffee;
public CoffeeDecorator(Coffee coffee){
this.coffee = coffee;
}
public void drink(){
coffee.drink();
}

}

public class Latte extends CoffeeDecorator {

public Latte(Coffee coffee) {
super(coffee);
}

void addSomething() {
System.out.println("add some milk");
}

public void drink(){
this.addSomething();
super.drink();
}

}

public class Mocha extends CoffeeDecorator{

public Mocha(Coffee coffee) {
super(coffee);
}

void addSomething() {
System.out.println("add some chocolates");

}
public void drink(){
addSomething();
super.drink();
}
}

 

public class Person {
public static void main(String[] args) {
Coffee coffee = new Coffee();
CoffeeDecorator latte = new Latte(new Mocha(coffee));
latte.drink();
}
}

///：输出结果

add some milk
add some chocolates
drink coffee

 

 

错误代码：

public class Coffee{
public void drink(){
System.out.println("drink coffee");
}
}

 

public abstract class CoffeeDecorator extends Coffee{
protected Coffee coffee;
public CoffeeDecorator(Coffee coffee){
this.coffee = coffee;
}

public void drinkcoffee(){
coffee.drink();
}

}

 

public class Latte extends CoffeeDecorator {

public Latte(Coffee coffee) {
super(coffee);
}

void addSomething() {
System.out.println("add some milk");
}

public void drinkcoffee(){
this.addSomething();
super.drinkcoffee();
}

}

 

public class Mocha extends CoffeeDecorator{

public Mocha(Coffee coffee) {
super(coffee);
}

void addSomething() {
System.out.println("add some chocolates");

}
public void drinkcoffee(){
addSomething();
super.drinkcoffee();
}
}

 

public class Person {
public static void main(String[] args) {
Coffee coffee = new Coffee();
CoffeeDecorator latte = new Latte(new Mocha(coffee));
latte.drinkcoffee();
}
}

///：输出结果

add some milk
drink coffee

 

错误原因：

Latte的super.drinkcoffee();会走到coffee.drink（），虽然Mocha也是Coffee，但是Mocha没有drink方法，不会向下绑定到Mocha，直接走了CoffeeDecorator的drinkcoffee方法

装饰着模式的原因：

因为动态绑定的机制，会自动执行子类的方法，所以同样的调用会不停调用每个实现类的相同方法，以此实现装饰