参考文档：Java排序: Comparator vs Comparable 入门
java类经常面临排序问题，据我所知：java提供comparable和comparator两种比较方式：
1. comparable方法需要排序的类继承comparable接口，重写compareTo函数，但是只能实现一种对比方法（重写compareTo一次），例如:
类定义如下：
class Student implements Comparable<Student> {
private String name;
private String key;
private float score;
private int age;
public Student(String key, String name, float score, int age) {
this.key = key;
this.name = name;
this.score = score;
this.age = age;
}
@Override
/*
public int compareTo(Student ano) {
if (this.score < ano.score)
return -1;
if (this.score > ano.score)
return 1;
else {
if (this.age > ano.age)
return 1;
if (this.age < ano.age)
return -1;
else
return 0;
}//else
}//compareTo
*/
public int compareTo(Student ano){
return (int)(this.score - ano.score);
}
}
可以看到compareTo被我们重写，接下来我们可以运行排序，然后观察运行结果：
Student stus[] = {new Student("lee","9527",22,80)
,new Student("zhang","1839",23,83)
,new Student("zhao","1284",21,80)};
print(stus);
Arrays.sort(stus);
System.out.println("after sorted:");
print(stus);
运行结果如下：
Student{name=‘9527‘, key=‘lee‘, score=22.0, age=80}
Student{name=‘1839‘, key=‘zhang‘, score=23.0, age=83}
Student{name=‘1284‘, key=‘zhao‘, score=21.0, age=80}
after sorted:
Student{name=‘1284‘, key=‘zhao‘, score=21.0, age=80}
Student{name=‘9527‘, key=‘lee‘, score=22.0, age=80}
Student{name=‘1839‘, key=‘zhang‘, score=23.0, age=83}
扩展：对元素是自定义类的List进行排序，自定List定义如下：
public static List<Student> getStudents(){
List<Student> col = new ArrayList<Student>();
Random rand = new Random();
String valkey;
int valAge, valScore;
String valName;
for (int i = 0; i < 10; i++) {
valkey = UUID.randomUUID().toString();
valName = RandomStringUtils.random(10, 20, 110, true, true);
valAge = rand.nextInt(80);
valScore = rand.nextInt(80);
col.add(new Student(valkey,valName, valAge, valScore));
}
return col;
}
通过Collections.sort(List)方法进行排序：
List<Student> grade = Student.getStudents();
Iterator<Student> iter = grade.iterator();
Collections.sort(grade);
while(iter.hasNext()) {
//iter.next();
System.out.println(iter.next().toString());
}
2. 有时候我们需要对多种关键字进行排序，那么我们需要通过实现java.util.Comparator来实现，我们可以对类Student任何字段进行排序。我们不需要改变类Student，类本身不用实现java.lang.Comparable或者是java.util.Comparator接口，代码如下：
class studSortByName implements Comparator<Student> {
public int compare(Student st1, Student st2){
return st1.getName().compareTo(st2.getName());
}
}
接下来我们通过排序进行测验，我们必须使用Collections.sort(List, Comparator)这个方法而不是Collections.sort(List)方法：
public class ClassSort {
public static void main(String []args) {
//Student stu1 = new Student("wen", 90, 17);
//Student stu2 = new Student("mike", 90, 18);
//System.out.print("res:" + stu1.compareTo(stu2));
List<Student> grade = Student.getStudents();
Iterator<Student> iter = grade.iterator();
//Collections.sort(grade);
Collections.sort(grade,new StudSortByName());
while(iter.hasNext()) {
//iter.next();
System.out.println(iter.next().toString());
}
/*Student stus[] = {new Student("lee","9527",22,80)
,new Student("zhang","1839",23,83)
,new Student("zhao","1284",21,80)};
print(stus);
Arrays.sort(stus);
System.out.println("after sorted:");
print(stus);
*/
}
public static void print(Student [] stus){
for (int i = 0; i < stus.length; i++) {
System.out.println(stus[i].toString());
}
}
}
附注可执行代码如下:
package comparable;
import java.util.*;
import org.apache.commons.lang3.RandomStringUtils;
import org.apache.commons.lang3.builder.Diff;
/**
* Created by carl on 11/7/15.
*/
class Student implements Comparable<Student> {
private String name;
private String key;
private float score;
private int age;
public Student(String key, String name, float score, int age) {
this.key = key;
this.name = name;
this.score = score;
this.age = age;
}
@Override
/*
public int compareTo(Student ano) {
if (this.score < ano.score)
return -1;
if (this.score > ano.score)
return 1;
else {
if (this.age > ano.age)
return 1;
if (this.age < ano.age)
return -1;
else
return 0;
}//else
}//compareTo
*/
public int compareTo(Student ano){
return (int)(this.score - ano.score);
}
public static List<Student> getStudents(){
List<Student> col = new ArrayList<Student>();
Random rand = new Random();
String valkey;
int valAge, valScore;
String valName;
for (int i = 0; i < 10; i++) {
valkey = UUID.randomUUID().toString();
valName = RandomStringUtils.random(10, 20, 110, true, true);
valAge = rand.nextInt(80);
valScore = rand.nextInt(80);
col.add(new Student(valkey,valName, valAge, valScore));
}
return col;
}
public String getName(){
return name;
}
public float getScore() {
return score;
}
public int getAge() {
return age;
}
@Override
public String toString() {
return "Student{" +
"name=‘" + name + ‘\‘‘ +
", key=‘" + key + ‘\‘‘ +
", score=" + score +
", age=" + age +
‘}‘;
}
}//Student
class StudSortByName implements Comparator<Student> {
public int compare(Student st1, Student st2){
return st1.getName().compareTo(st2.getName());
}
}
public class ClassSort {
public static void main(String []args) {
//Student stu1 = new Student("wen", 90, 17);
//Student stu2 = new Student("mike", 90, 18);
//System.out.print("res:" + stu1.compareTo(stu2));
List<Student> grade = Student.getStudents();
Iterator<Student> iter = grade.iterator();
//Collections.sort(grade);
Collections.sort(grade,new StudSortByName());
while(iter.hasNext()) {
//iter.next();
System.out.println(iter.next().toString());
}
/*Student stus[] = {new Student("lee","9527",22,80)
,new Student("zhang","1839",23,83)
,new Student("zhao","1284",21,80)};
print(stus);
Arrays.sort(stus);
System.out.println("after sorted:");
print(stus);
*/
}
public static void print(Student [] stus){
for (int i = 0; i < stus.length; i++) {
System.out.println(stus[i].toString());
}
}
}
时间： 2024-10-10 02:52:39