Question

java语言看下图,对象数组,能根据对象的某种属性对数组对象进行排序吗?

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

Answer 1

两个方法，一是被比较的类实现Comparable接口，二是使用Comparator比较器。

两种方法各有优劣：

第一种方法：一个类只能有一种比较方法，当需要多种比较方法时，无法实现。

常用的方法是，用第一种方法实现一种默认的，最常用的比较方法。需要其他比较方法时在使用第二种模式。

这是数组类的。

import java.util.Arrays;
import java.util.Comparator;
public class SortDemo {
    public static void main(String[] args) {
        Student[] array = new Student[] {
                new Student("A", 80),
                new Student("B", 60),
                new Student("C", 70),
                new Student("D", 100),
                new Student("E", 90) };
        printArray(array);
        Arrays.sort(array);
        System.out.println("After Sort");
        printArray(array);
        Arrays.sort(array, new Comparator<Student>() {
            public int compare(Student s1, Student s2) {
                return s2.score - s1.score;
            }
        });
        System.out.println("After Sort2");
        printArray(array);
    }
    private static void printArray(Object[] array) {
        for (Object o : array) {
            System.out.println(o);
        }
    }
}
class Student implements Comparable<Student> {
    public String name;
    public int score;
    public Student() {
    }
    public Student(String name, int score) {
        this.name = name;
        this.score = score;
    }
    public String toString() {
        return "Student " + name + " : " + score;
    }
    public int compareTo(Student other) {
        return this.score - other.score;
    }
}

这是容器类的。

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class SortDemo {
    public static void main(String[] args) {
        List<Student> list = new ArrayList();
        list.add(new Student("A", 80));
        list.add(new Student("B", 60));
        list.add(new Student("C", 70));
        list.add(new Student("D", 100));
        list.add(new Student("E", 90));
        printList(list);
        Collections.sort(list);
        System.out.println("After Sort");
        printList(list);
        Collections.sort(list, new Comparator<Student>() {
            public int compare(Student s1, Student s2) {
                return s2.score - s1.score;
            }
        });
        System.out.println("After Sort2");
        printList(list);
    }
    private static void printList(List<Student> list) {
        for (Student s : list) {
            System.out.println(s);
        }
    }
}
class Student implements Comparable<Student> {
    public String name;
    public int score;
    public Student() {
    }
    public Student(String name, int score) {
        this.name = name;
        this.score = score;
    }
    public String toString() {
        return "Student " + name + " : " + score;
    }
    public int compareTo(Student other) {
        return this.score - other.score;
    }
}

Answer 2

//给name和score加个static
//自己写排序的方法，纯手动，若有代码错误请见谅，思路无误
public void sortTest(Student[] test){
    Student s=new Student();
    for(int i=0;i<test.length;i++){
        for(int j=test.length-1;j>i;j--){
            if(test[j].score<test[j-1].score){
                s=test[j];
                test[j]=test[j-1];
                test[j-1]=s;
            }
        }
    }
}