在讀《efficitive java》第12條：考慮實現Comparable介面

使用Comparable介面按物件按屬性的優先順序排序還是比較方便的
例項程式碼

package com.ctc.basic;

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

public class Student implements Comparable<Student> {

    private int number;

    private String name;

    private
 
 float score;

    public Student(int number, String name, float score) {
        this.number = number;
        this.name = name;
        this.score = score;
    }

    //排序優先順序number-name-score
    @Override
    public int compareTo(Student c) {
        // 如果number不等按number排序（增序
        if (this.number != c.number) {
            return
 
 this.number > c.number ? 1 : -1;
        } else {
            // 如果number和name都相等按score排序（降序）
            if (this.name.equals(c.name)) {
                return this.score < c.score ? 1 : -1;
            }
            // 如果number相等按name排序（增序）
            return this.name.compareTo(c.name) > 0 ? 1
 
 : -1;
        }
    }

    @Override
    public String toString() {
        return "Student [number=" + number + ", name=" + name + ", score=" + score + "]";
    }

    public static void main(String[] args) {
        List<Student> students = new ArrayList<Student>() {
            {
                add(new Student(1, "a", 2));
                add(new Student(3, "a", 3));
                add(new Student(7, "a", 5));
                add(new Student(5, "a", 2));
                add(new Student(3, "a", 2));
                add(new Student(7, "c", 2));
                add(new Student(1, "b", 5));
                add(new Student(7, "a", 2));
                add(new Student(7, "c", 10));

            }
        };

        Collections.sort(students);
        for (Student student : students) {
            System.out.println(student);
        }
    }
}

輸出結果為

Student [number=1, name=a, score=2.0]
Student [number=1, name=b, score=5.0]
Student [number=3, name=a, score=3.0]
Student [number=3, name=a, score=2.0]
Student [number=5, name=a, score=2.0]
Student [number=7, name=a, score=5.0]
Student [number=7, name=a, score=2.0]
Student [number=7, name=c, score=10.0]
Student [number=7, name=c, score=2.0]