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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()); } } }
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原文地址：http://www.cnblogs.com/wenwangt/p/4946271.html
