结合使用组合（composition）和继承（inheritance）

同时使用组合和继承是很常见的事。下例就展示了同时使用这两种技术，并配以必要的构造
器初始化，来创建更加复杂的类：
 
//:c06:PlaceSetting.java
// Combiningcomposition & inheritance.
import com.bruceeckel.simpletest.*;

 
class Plate {
  Plate(int i) {
    System.out.println("Plate constructor");
  }
}
 
class DinnerPlate    
extends Plate {
  DinnerPlate(int i) {
super(i);
    System.out.println("DinnerPlate constructor");
  }
}
 
class Utensil {
  Utensil(int i) {

 
 
 
    System.out.println("Utensil constructor");
  }
}
 
class Spoon 
extends Utensil {
  Spoon(int i) {
super(i);
    System.out.println("Spoon constructor");
  }
}
 
class Fork   
extends Utensil {
  Fork(int i) {
super(i);
    System.out.println("Fork constructor");

  }
}
 
class Knife  
extends Utensil {
  Knife(int i) {
super(i);
    System.out.println("Knife constructor");
  }
}
 
// A culturalway of doing something:
class Custom {
  Custom(int i) {
    System.out.println("Custom constructor");

  }
}
 
public  class PlaceSetting
extends Custom {
private   static Test monitor =
new Test();
private Spoon sp;
private Fork frk;
private Knife kn;
private DinnerPlate pl;
public PlaceSetting(int i) {

super(i + 1);
    sp = new Spoon(i + 2);
    frk =   new Fork(i + 3);
    kn = new Knife(i + 4);
    pl = new DinnerPlate(i + 5);

 
 
 
    System.out.println("PlaceSetting constructor");

  }
public   static    void main(String[] args) {

    PlaceSetting x = new PlaceSetting(9);
    monitor.expect(new String[] {

"Customconstructor",
"Utensilconstructor",
"Spoonconstructor",
"Utensilconstructor",
"Forkconstructor",
"Utensilconstructor",
"Knifeconstructor",
"Plateconstructor",
"DinnerPlateconstructor",
"PlaceSettingconstructor"
    });
  }
}   ///:~
 
虽然编译器强制你去初始化基类，并且要求你要在构造器起始处就要这么做，但是它并不监
督你必须将成员对象也初始化，因此在这一点上你自己必须时刻注意。