// generics/CoffeeDecoration38.java
// TIJ4 Chapter Generics, Exercise 38, page 719
// Create a simple Decorator system by starting with basic coffee, then
// providing decorators of steamed milk, foam, chocolate, caramel and 
// whipped cream.
import java.util.*;

class BasicCoffee {
    private static long counter = 0;
      private final long id = counter++;
    private String value;
    public void set(String val) { value = val; }
    public String get() { return value; }
      public String toString() {
            return getClass().getSimpleName() + " " + id;
      }
}

class Decorator extends BasicCoffee {
    protected BasicCoffee basicCoffee;
    public Decorator(BasicCoffee basicCoffee) { 
        this.basicCoffee = basicCoffee; 
    }
    public void set(String val) { basicCoffee.set(val); }
    public String get() { return basicCoffee.get(); }
}

class SteamedMilk extends Decorator {
    private final String steamedMilk = "steamedMilk";
    public SteamedMilk(BasicCoffee basicCoffee) {
        super(basicCoffee);
    }
    public String getSteamedMilk() { return steamedMilk; }
}

class Foam extends Decorator {
    private final String foam = "foam";
    public Foam(BasicCoffee basicCoffee) {
        super(basicCoffee);
    }
    public String getFoam() { return foam; }
}

class Chocolate extends Decorator {
    private final String chocolate = "chocolate";
    public Chocolate(BasicCoffee basicCoffee) {
        super(basicCoffee);
    }
    public String getChocolate() { return chocolate; }
}

class Caramel extends Decorator {
    private final String caramel = "caramel";
    public Caramel(BasicCoffee basicCoffee) {
        super(basicCoffee);
    }
    public String getCaramel() { return caramel; }
}

class WhippedCream extends Decorator {
    private final String whippedCream = "whippedCream";
    public WhippedCream(BasicCoffee basicCoffee) {
        super(basicCoffee);
    }
    public String getWhippedCream() { return whippedCream; }
}

public class CoffeeDecoration38 {
    public static void main(String[] args) {
        SteamedMilk sm = new SteamedMilk(new BasicCoffee());
        SteamedMilk sm2 = new SteamedMilk(
            new Foam(new BasicCoffee()));
        Chocolate c = new Chocolate(new BasicCoffee());
        WhippedCream wc = new WhippedCream(new Caramel(
            new Chocolate(new Foam(new SteamedMilk(
            new BasicCoffee())))));
    }
}

------解决方案--------------------
上网搜搜

------解决方案--------------------
class A {
private String a;//1
public A() {//2
}
}

class B extends A {
private string b;//3
public B()//4 {
}
}

main() {
B b = new B();
}

b的初始化时，上面标识的1,2,3,4的执行顺序