java 对象排序

Java API针对集合类型排序提供了两种支持：
java.util.Collections.sort(java.util.List)
java.util.Collections.sort(java.util.List, java.util.Comparator)
 
第一个方法要求所排序的元素类必须实现java.lang.Comparable接口。
第二个方法要求实现一个java.util.Comparator接口。
 
java.lang.Comparable接口和java.util.Comparator接口是Java对排序最提供最基本支持。这两个接口不但可以用于集合元素排序，还可以用于数组排序。

 

 

/**
 * @(#) Student.java Created on 2013-1-7
 *
 * Copyright (c) 2013 Aspire. All Rights Reserved
 */
package com.braver.test;

import java.util.Comparator;

/**
 * The class <code>Student</code>
 * 
 * @author ouyangfeng
 * @version 1.0
 */
public final class Student {

    private String name;

    private int age;
    
    /**
     * Constructor
     * 
     * @param name
     * @param age
     */
    public Student(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }

    /**
     * Getter of name
     * 
     * @return the name
     */
    public String getName() {
        return name;
    }

    /**
     * Setter of name
     * 
     * @param name
     *            the name to set
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * Getter of age
     * 
     * @return the age
     */
    public int getAge() {
        return age;
    }

    /**
     * Setter of age
     * 
     * @param age
     *            the age to set
     */
    public void setAge(int age) {
        this.age = age;
    }


    /**
     * {@inheritDoc}
     * @see java.lang.Object#toString()
     */
    @Override
    public String toString() {
        final StringBuilder builder = new StringBuilder();
        builder.append("name:").append(name).append(" age:").append(age);
        return builder.toString();
    }
    
    public static final class StudentComparator implements Comparator<Student> {

        
        
        /**关键点在这里
         * {@inheritDoc}
         * 
         * @see java.util.Comparator#compare(java.lang.Object, java.lang.Object)
         */
        @Override
        public int compare(Student o1, Student o2) {
//            if (o1.getAge() < o2.age)
//                return -1;
//            else if (o1.getAge() == o2.getAge())
//                return 0;
//            else
//                return 1;
            return o1.getName().compareTo(o2.getName());
        }

    }

}

 测试方法

/**
 * @(#) StudentMain.java Created on 2013-1-7
 *
 * Copyright (c) 2013 Aspire. All Rights Reserved
 */
package com.braver.test;

import java.util.ArrayList;
import java.util.Collections;

import com.braver.test.Student.StudentComparator;

/**
 * The class <code>StudentMain</code>
 *
 * @author ouyangfeng
 * @version 1.0
 */
public final class StudentMain {

    /**
     * @param args
     */
    public static void main(String[] args) {
        Student student = new Student("aname1", 18);
        Student student2 = new Student("dname2", 19);
        Student student3 = new Student("bname3", 20);
        
        ArrayList<Student> list = new ArrayList<Student>();
        list.add(student);
        list.add(student2);
        list.add(student3);
        
        Collections.sort(list, new StudentComparator());
        
        for(Student stu : list){
            System.out.println(stu);
        }
    }

}