java比较器Comparable接口和Comparator接口的区别及应用

java的比较器有两类，分别是Comparable接口和Comparator接口。
在为对象数组进行排序时，比较器的作用非常明显，首先来讲解Comparable接口。

让需要进行排序的对象实现Comparable接口，重写其中的compareTo(Object obj)方法，在其中定义排序规则，那么就可以直接调用java.util.Arrays.sort()来排序对象数组,当用集合例如ArrayList代替数组时,可直接调用Collections.sort();

public int compareTo(Object obj)
	{
		AutoStudent ast = (AutoStudent) obj;
		if(this.height==ast.height)
		{
			return ast.name.compareTo(this.name);
		}
		else
		{
			return this.height-ast.height;//身高按从低到高
		}
	}

Comparator接口中必须要实现的compare(Object obj1,Object obj2 )有两个参数。

public class StudentComparactor implements Comparator<StudentCom>
{
		public int compare(StudentCom sc1, StudentCom sc2)
		{
			if(sc1.getHeight().compareTo(sc2.getHeight())>0)
				return 1;
			if(sc1.getHeight().compareTo(sc2.getHeight())<0) 
				return -1;
			else
			{
				if(sc1.getName().compareTo(sc2.getName())>0) 
					return 1;
				if(sc1.getName().compareTo(sc2.getName())<0) 
					return -1;
			}
			return 0;
		}
}

package ch7;



public class AutoStudent implements Comparable<AutoStudent>{  //<Object>
	private String name;
	private int  height;
	AutoStudent ()  {}
	AutoStudent(String name,int  height) 
	{
		this.name=name;
		this.height=height;
	}
    public void setName(String name)
    {
    	this.name=name;
    }
    public String getName()
    {
    	return name;
    }
    public void setHeight(int height)
    {
    	this.height=height;
    }
    public int  getHeight()
    {
    	return height;
    }
    public String toString()
    {
    	return name+"同学的身高是："+height+"厘米";
    }
    public boolean equals(Object obj)         //重写equals方法
    {
    	if(obj instanceof AutoStudent)
    	{
    		AutoStudent r = (AutoStudent) obj;
    		if(r.name.equals(this.name)&&r.height==this.height)
    			return true;
    	}
    	return false;
    }
    public int hashCode(){						//重写hashCode方法
		return name.hashCode()^height;				
	}
	public int compareTo(AutoStudent ast) {
		if(this.height==ast.height)
		{
			return this.name.compareTo(ast.name);
		}
		else
		{
			return this.height-ast.height;    //按从低到高排列
		}
	}
	/*
	public int compareTo(Object obj)
	{
		AutoStudent ast = (AutoStudent) obj;
		if(this.height==ast.height)
		{
			return ast.name.compareTo(this.name);
		}
		else
		{
			return this.height-ast.height;//身高按从低到高
		}
	}
	*/
}

package ch7;

import java.util.*;
public class AutoStudentText
{
	public static void main(String[] args) 
	{
		List <AutoStudent> list = new ArrayList <AutoStudent> ();
		AutoStudent s1 = new AutoStudent("liming",167);
		AutoStudent s2 = new AutoStudent("libai",155);
		AutoStudent s3 = new AutoStudent("caicai",180);
		AutoStudent s4 = new AutoStudent("weilai",160);
		AutoStudent s5 = new AutoStudent("chali",160);
		list.add(s1);
		list.add(s2);
		list.add(s3);
		list.add(s4);
		list.add(s5);
		Collections.sort(list);
		Iterator  <AutoStudent>it = list.iterator();
		while(it.hasNext())
		{
			System.out.println(it.next());
		}
	}

}

package ch7;

public class StudentCom
{
	private Integer height;						
	private String name;
	
	public StudentCom() {}//无参构造方法

	public StudentCom(Integer height, String name) 
	{	                                            //有参构造方法
		this.height = height;
		this.name = name;
	}

	
	public Integer getHeight()
	{
		return height;
	}

	public void setHeight(Integer height)
	{
		this.height = height;
	}

	public String getName() 
	{
		return name;
	}

	public void setName(String name) 
	{
		this.name = name;
	}
	
	@Override
	public String toString() 
	{				//重写toString方法
		return name + "同学的身高是: " + height +"厘米";	
	}
	@Override
	public boolean equals(Object obj)
	{		//重写equals方法
		if(obj instanceof StudentCom)
		{
			StudentCom ast=(StudentCom)obj;
			if(ast.name.equals(this.name) && ast.height==this.height)
			{
				return true;
			}
		}
		return false;
	}
	@Override
	public int hashCode()
	{						//重写hashCode方法
		return name.hashCode()^height;				
	}
}

package ch7;

import java.util.Comparator;

/*
 * 构建一个StudentComparator类,实现Comparator接口,用来在构建集合的时候传入
 * 按照身高进行排列，身高相同的按照名字的字典顺序排列
 */
public class StudentComparactor implements Comparator<StudentCom>
{
		public int compare(StudentCom sc1, StudentCom sc2)
		{
			if(sc1.getHeight().compareTo(sc2.getHeight())>0)
				return 1;
			if(sc1.getHeight().compareTo(sc2.getHeight())<0) 
				return -1;
			else
			{
				if(sc1.getName().compareTo(sc2.getName())>0) 
					return 1;
				if(sc1.getName().compareTo(sc2.getName())<0) 
					return -1;
			}
			return 0;
		}
}

package ch7;

import java.util.Iterator;
import java.util.SortedSet;
import java.util.TreeSet;

public class TestComparator 
{
	public static void main(String[] args) 
	{
		//构建集合，传入学生比较器
		SortedSet<StudentCom> ss = new TreeSet<StudentCom>(new StudentComparactor());
		StudentCom sc1 = new StudentCom(160,"lily");
		StudentCom sc2 = new StudentCom(165,"zhangsan");
		StudentCom sc3 = new StudentCom(172,"wangwu");
		StudentCom sc4 = new StudentCom(193,"lisi");
		StudentCom sc5 = new StudentCom(178,"zhaoliu");
		StudentCom sc6 = new StudentCom(180,"zhuba");
		StudentCom sc7 = new StudentCom(172,"mike");
		StudentCom sc8 = new StudentCom(172,"jim");
		StudentCom sc9 = new StudentCom(172,"andy");
		
		//向集合ss中添加元素，即学生站到队伍里
		ss.add(sc1);
		ss.add(sc2);
		ss.add(sc3);
		ss.add(sc4);
		ss.add(sc5);
		ss.add(sc6);
		ss.add(sc7);
		ss.add(sc8);
		ss.add(sc9);
		//遍历输出，按照要求排序
		Iterator <StudentCom>it=ss.iterator();
		while(it.hasNext())
		{
			System.out.println(it.next());
		}
	}
}