Java中類的組合

一.概念

　　在新類中簡單創建原有類的對象，即一個類的對象是另外一個類中的成員。其操作方法是將已經存在類的對象放到新類中即可。

例：廚房（Kitchen）中有爐子（cooker）和冰箱（refrigerator）。

class Cooker{//類的語句}
class Refrigerator{//類的語句}
class Kitchen{
	Cooker myCooker;
	Refrigerator myRefrigerator;
}　　

例：線段類--一個線段類包含兩個端點。

public class Point //點類
{
	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.組合與繼承的結合

class Plate{//聲明盤子
	public Plate(int i){
		System.out.println("Plate constructor");
	}
}

class DinnerPlate extends Plate{//聲明餐盤為盤子的子類
	public DinnerPlate(int i){
		super(i);
		System.out.println("DinnerPlate constructor");
	}
}

class Utensil{//聲明器具
	Utensil(int i){
		System.out.println("Utensil constructor");
	}
}

class Spoon extends Utensil{//聲明勺子為器具的子類
	public Spoon(int i){
		super(i);
		System.out.println("Spoon constructor");
	}
}

class Fork extends Utensil{//聲明叉子為器具的子類
	public Fork(int i){
		super(i);
		System.out.println("Fork constructor");
	}
}

class Knife extends Utensil{//聲明餐刀為器具的子類
	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);
	}
}

//運行結果
Custom constructor
Utensil constructor
Spoon constructor
Utensil constructor
Fork constructor
Utensil constructor
Knife constructor
Plate constructor
DinnerPlate constructor
PlaceSetting constructor