java比較子Comparable介面和Comaprator介面

java的比較子有兩類，分別是Comparable介面和Comparator介面。

在為對象數組進行排序時，比較子的作用非常明顯，首先來講解Comparable介面。

讓需要進行排序的對象實現Comparable介面，重寫其中的compareTo(T o)方法，在其中定義定序，那麼就可以直接調用java.util.Arrays.sort()來排序對象數組，執行個體如下：

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，為什麼能夠直接調用,這是因為在Student類內部            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);        }    }}

程式運行結果:

sunliu 22 100.0
wangwu 20 99.0
zhangsan 20 90.0
lisi 22 90.0

但是在設計類的時候，往往沒有考慮到讓類實現Comparable介面，那麼我們就需要用到另外的一個比較子介面Comparator。

從上面的執行個體我們可以發現，compareTo(T o)只有一個參數，而Comparator介面中必須要實現的compare(T o1,T o2)就有兩個參數。

代碼執行個體：

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);        }    }}

上述程式的運行結果與代碼執行個體1一樣。