java的比較器有兩類，分別是Comparable接口和Comparator接口。
在為對象數組進行排序時，比較器的作用非常明顯，首先來講解Comparable接口。
讓需要進行排序的對象實現Comparable接口，重寫其中的compareTo(T o)方法，在其中定義排序規則，那么就可以直接調用java.util.Arrays.sort()來排序對象數組，實例如下：
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，為什么能夠直接調用,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);
}
}
}
程序運行結果:
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接口，那么我們就需要用到另外的一個比較器接口Comparator。
從上面的實例我們可以發現，compareTo(T o)只有一個參數，而Comparator接口中必須要實現的compare(T o1,T o2)就有兩個參數。
代碼實例：
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);
}
}
}
