2020年8月31日 定制比较Comparator接口 和 自然比较Comparable接口 Arrays的两种sort方法

package test04;

public class TestComparator2 {
    public static void main(String[] args) {
        Student[] all = new Student[5];
        all[0] = new Student("杨洪强", 24, 89);
        all[1] = new Student("苏海波", 23, 100);
        all[2] = new Student("张三",23,88);
        all[3] = new Student("李四",24,44);
        all[4] = new Student("王五",25,45);
        
        AgeComparator c = new AgeComparator();
        MyArrays.sort(all, c);
        
        for (int i = 0; i < all.length; i++) {
            System.out.println(all[i]);
        }
    }
}

package test04;

public class Student {
    String name;
    int age;
    int score;
    public Student(String name, int age, int score) {
        super();
        this.name = name;
        this.age = age;
        this.score = score;
    }
    public Student() {
        super();
    }
    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 int getScore() {
        return score;
    }
    public void setScore(int score) {
        this.score = score;
    }
    @Override
    public String toString() {
        return "Student [name=" + name + ", age=" + age + ", score=" + score + "]";
    }
}

package test04;

import java.util.Comparator;

/*
 * 需求：编写一个MyArrays的数组工具类，这个工具类，想要为任意的对象数组，进行升序排序
 */
public class MyArrays {
    public static void sort(Object[] arr,Comparator c){
        for (int i = 1; i < arr.length; i++) {
            for (int j = 0; j < arr.length-1; j++) {
//                System.out.println("比较：arr["+j+"]和arr["+(j+1)+"]");
//                System.out.println(arr[j]);
//                System.out.println(arr[j+1]);
//                System.out.println();
                
                if(c.compare(arr[j], arr[j+1])>0){
                    Object temp = arr[j];
                    arr[j] = arr[j+1];
                    arr[j+1] = temp;
                }
            }
        }
    }
}

package test04;

import java.util.Comparator;

public class AgeComparator implements Comparator {

    @Override
    public int compare(Object o1, Object o2) {
        Student s1 = (Student) o1;
        Student s2 = (Student) o2;
        return s1.getAge() - s2.getAge();
    }
    
}

定制比较器的使用图解

 自然比较器

package com.atguigu.test05;

import java.util.Arrays;

/*
 * 总结：
 * Arrays的sort方法有两种：
 * （1）void sort(Object[] arr)：
 *         根据元素的自然顺序对指定对象数组按升序进行排序。数组中的所有元素都必须实现 Comparable 接口。
 * （2）void sort(Object[] arr, Comparator c)：
 *         根据“指定比较器”产生的顺序对指定对象数组进行排序。数组中的所有元素都必须是通过“指定比较器”可相互比较的
 */

public class TestArrays {
    public static void main(String[] args) {
        Student[] all = new Student[5];
        all[0] = new Student("杨洪强", 24, 89);
        all[1] = new Student("苏海波", 23, 100);
        all[2] = new Student("张三",23,88);
        all[3] = new Student("李四",24,44);
        all[4] = new Student("王五",25,45);
        
        //如果我们的学生类Student，实现了java.lang.Comparable接口，
        //能不能按照自然排序的规则进行排序呢
        //Arrays中有这样的方法
        //public static void sort(Object[] a)
        
        Arrays.sort(all);//这里面排序过程中，调用了元素本身的compareTo()方法
        //因为元素本身是Student类型，它实现了java.lang.Comparable接口
        //本身就具备比较大小的能力，即拥有compareTo()方法
        
        for (int i = 0; i < all.length; i++) {
            System.out.println(all[i]);
        }
    }
}

package com.atguigu.test05;

/*
 * java.util.Comparator：定制比较，定制顺序
 *         int compare(Object o1, Object o2)：
 *                 o1与o2比较，o1>o2，返回正整数
 *                 o1与o2比较，o1<o2，返回负整数
 *                 o1与o2比较，o1=o2，返回0
 * java.lang.Comparable：自然比较，自然顺序
 *         int compareTo(Object obj)
 *                 this与obj对象比较，this > obj，返回正整数
 *                 this与obj对象比较，this < obj，返回负整数
 *                 this与obj对象比较，this = obj，返回0
 * 
 * 上午讲的定制比较器，用定制比较器的对象，比较两个学生对象：
 *         AgeComparator c = new AgeComparator();
 *         if(c.compare(s1, s2) > 0){...}
 * 
 * 希望学生对象本身就具备比较大小的能力。
 */
public class TestComparable {
    public static void main(String[] args) {
        Student s1 = new Student("杨洪强", 24, 89);
        Student s2 = new Student("苏海波", 23, 100);
        
        //按成绩比较
        if(s1.compareTo(s2)>0){
            System.out.println("s1 > s2成绩");
        }else if(s1.compareTo(s2)<0){
            System.out.println("s1 < s2成绩");
        }else{
            System.out.println("s1 = s2成绩");
        }
        
        //按年龄比较，只能再用定制比较，补充完成这个功能
    }
}
class Student implements Comparable{
    private String name;
    private int age;
    private int score;
    public Student(String name, int age, int score) {
        super();
        this.name = name;
        this.age = age;
        this.score = score;
    }
    public Student() {
        super();
    }
    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 int getScore() {
        return score;
    }
    public void setScore(int score) {
        this.score = score;
    }
    @Override
    public String toString() {
        return "Student [name=" + name + ", age=" + age + ", score=" + score + "]";
    }
    @Override
    public int compareTo(Object obj) {
        //this与obj比较，this和obj都是学生对象
        Student other = (Student) obj;
        //例如：对于学生对象来说，最常用的是按成绩排名，那么我就可以把自然顺序定位成绩升序
/*        if(this.score > other.score){
            return 1;
        }else if(this.score < other.score){
            return -1;
        }
        return 0;*/
        
        return this.score - other.score;
    }
}