一.概念
在新类中简单创建原有类的对象，即一个类的对象是另外一个类中的成员。其操作方法是将已经存在类的对象放到新类中即可。
例：厨房（Kitchen）中有炉子（cooker）和冰箱（refrigerator）。
class Cooker{//类的语句}
class Refrigerator{//类的语句}
class Kitchen{
Cooker myCooker;
Refrigerator myRefrigerator;
}
例：线段类--一个线段类包含两个端点。
public class Point //点类
{
private int x,y;
public Point(int x,int y)
{
this.x = x;
this.y = y;
}
public int GetX()
{
return x;
}
public inr GetY()
{
return y;
}
}
class Line
{
private Point p1,p2;
Line(Point a,Point b)
{
p1 = new Point(a.GetX(),a.GetY());
p2 = new Point(b.GetX(),b.GetY());
}
public double Length()
{
return Math.sqrt(Math.pow(p2.GetX() - p1.GetX(),2)
+ Math.pow(p2.GetY() - p1.GetY(),2));
}
}
二.组合与继承的结合
class Plate{//声明盘子
public Plate(int i){
System.out.println("Plate constructor");
}
}
class DinnerPlate extends Plate{//声明餐盘为盘子的子类
public DinnerPlate(int i){
super(i);
System.out.println("DinnerPlate constructor");
}
}
class Utensil{//声明器具
Utensil(int i){
System.out.println("Utensil constructor");
}
}
class Spoon extends Utensil{//声明勺子为器具的子类
public Spoon(int i){
super(i);
System.out.println("Spoon constructor");
}
}
class Fork extends Utensil{//声明叉子为器具的子类
public Fork(int i){
super(i);
System.out.println("Fork constructor");
}
}
class Knife extends Utensil{//声明餐刀为器具的子类
public Knife(int i){
super(i);
System.out.println("Knife constructor");
}
}
class Custom{
public Custom(int i){
System.out.println("Custom constructor");
}
}
public class PlaceSetting extends Custom{
Spoon sp;Fork frk;Knife kn;
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);
}
}
//运行结果
Custom constructor
Utensil constructor
Spoon constructor
Utensil constructor
Fork constructor
Utensil constructor
Knife constructor
Plate constructor
DinnerPlate constructor
PlaceSetting constructor