java比较器Comparable接口和Comaprator接口

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：

View Code

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：

View Code

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);

        }

    }



}

上述程序的运行结果与代码实例1一样。