Comparable和Comparetor的使用方法

Comparable：

使用此接口需要重寫commpareTo函數。
格式：public int compareTo(Object o)

Comparetor：

可以單獨創建一個比較器類，也可創建爲內部類。
比較器類實現 Comparator接口，重寫compare。
格式： public int compare(Object o1,Object o2)

實例：

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1.抽象類和子類圖形類
抽象類

package Geometric;

abstract class GeometricObject
{	
	public abstract double getPerimeter();//周長
	public abstract double getArea();//面積
}

矩形

package Geometric;

public class Rectangle extends GeometricObject implements Comparable
{
	public double length = 0.00;//長度
	public double width = 0.00;//寬度
	
	public Rectangle(double length,double width)
	{
		this.length = length;
		this.width = width;
	}

	public double getPerimeter()
	{
		return (this.length+this.width)*2;	
	}
	
	public double getArea()
	{
		return this.length * this.width;
	}
	
	public int compareTo(Object o)
	{
		if(getArea()>((Rectangle)o).getArea())
			return 1;
		else if (getArea()==((Rectangle)o).getArea())
			return 0;
		else
			return -1;
	}
	
	public String toString()
	{
		
		return "矩形面積:"+getArea();
	}
}

圓形

package Geometric;

public class Circle extends GeometricObject 
{
	public double radius = 0.00;//半徑
	
	public Circle(double radius)
	{
		this.radius = radius;
	}
	

	public double getPerimeter()
	{
		return 2*3.14*this.radius;
	}
	
	public double getArea()
	{
		return 3.14 * this.radius *this.radius;
	}	
	
	public String toString()
	{
		return "圓形面積："+getArea();
	}
	
}

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2.面積比較器類

class AreaComparator implements Comparator<Geo>
{
	public int compare(Geo o1,Geo o2)
	{
		double a = o1.getArea();
		double b = o2.getArea();
		return (a>b?1:(a==b?0:-1));
 	}
}

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3.測試類

package Geometric;

import java.util.Collections;
import java.util.List;
import java.util.ArrayList;

public class ComparatorTest
{
	public static void main(String[] args)
	{
		//測試Comparable接口
		Rectangle re1= new Rectangle(3,8);
		Rectangle re2= new Rectangle(50,1);
		System.out.println(re1.compareTo(re2));
		System.out.println("******************");
		
		//測試Comparator比較器
		GeometricObject r1 = new Rectangle(1,2);
		GeometricObject r2 = new Rectangle(4,20);
		GeometricObject c1 = new Circle(4);
		List<GeometricObject> list = new ArrayList<GeometricObject>();
		list.add(r1);
		list.add(r2);
		list.add(c1);
		
		areaComparator myComparator = new areaComparator();
	    Collections.sort(list,myComparator);
	    for(GeometricObject p : list){
	          System.out.println(p.toString());
	      }
	}
}

4.運行結果