java比较器Comparable接口与Comaprator接口的深入分析

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(t o)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，实例如下：

class student implements comparable<student>{
    private string name;
    private int age;
    private float score;

    public student(string name, int age, float score) {
        this.name = name;
        this.age = age;
        this.score = score;
    }

    public string tostring()
    {
        return name+"\t\t"+age+"\t\t"+score;
    }
    @override
    public int compareto(student o) {
        // todo auto-generated method stub
        if(this.score>o.score)//score是private的，为什么能够直接调用,这是因为在student类内部
            return -1;//由高到底排序
        else if(this.score<o.score)
            return 1;
        else{
            if(this.age>o.age)
                return 1;//由底到高排序
            else if(this.age<o.age)
                return -1;
            else
                return 0;
        }
    }
}
public class comparabledemo01 {
    /**
     * @param args
     */
    public static void main(string[] args) {
        // todo auto-generated method stub
        student stu[]={new student("zhangsan",20,90.0f),
                new student("lisi",22,90.0f),
                new student("wangwu",20,99.0f),
                new student("sunliu",22,100.0f)};
        java.util.arrays.sort(stu);
        for(student s:stu)
        {
            system.out.println(s);
        }
    }
}

程序运行结果:
sunliu 22 100.0
wangwu 20 99.0
zhangsan 20 90.0
lisi 22 90.0
但是在设计类的时候，往往没有考虑到让类实现comparable接口，那么我们就需要用到另外的一个比较器接口comparator。
从上面的实例我们可以发现，compareto(t o)只有一个参数，而comparator接口中必须要实现的compare(t o1,t o2)就有两个参数。
代码实例：

package edu.sjtu.ist.comutil;
import java.util.comparator;
class student {
    private string name;
    private int age;
    private float score;

    public student(string name, int age, float score) {
        this.name = name;
        this.age = age;
        this.score = score;
    }
    public string getname() {
        return name;
    }
    public void setname(string name) {
        this.name = name;
    }
    public int getage() {
        return age;
    }
    public void setage(int age) {
        this.age = age;
    }
    public float getscore() {
        return score;
    }
    public void setscore(float score) {
        this.score = score;
    }
    public string tostring()
    {
        return name+"\t\t"+age+"\t\t"+score;
    }
}
class studentcomparator implements comparator<student>{
    @override
    public int compare(student o1, student o2) {
        // todo auto-generated method stub
        if(o1.getscore()>o2.getscore())
            return -1;
        else if(o1.getscore()<o2.getscore())
            return 1;
        else{
            if(o1.getage()>o2.getage())
                return 1;
            else if(o1.getage()<o2.getage())
                return -1;
            else
                return 0;
        }
    }

}
public class comparabledemo02 {
    /**
     * @param args
     */
    public static void main(string[] args) {
        // todo auto-generated method stub
        student stu[]={new student("zhangsan",20,90.0f),
                new student("lisi",22,90.0f),
                new student("wangwu",20,99.0f),
                new student("sunliu",22,100.0f)};
        java.util.arrays.sort(stu,new studentcomparator());
        for(student s:stu)
        {
            system.out.println(s);
        }
    }
}