Java 常用类库 之 比较类 Comparable

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/**
    知识点： 比较类 Comparable

    题目: 将某班学生按数学成绩从小到大排序

    思路:
        1. 抽象出类:
            1.1 班级(ClassSet)
            1.2 学生(Student)
        2. 找出类关系:
            2.1 学生 属于 班级 Student -> ClassSet(多对1)
        3. 找出类属性:
            3.1 ClassSet(班级名称,班级人数)
            3.2 Student(学生名称,数学成绩)
        4. 找出类方法:
            4.1 学生添加到班级 ClassSet{addStudent(Student s)}
            4.2 学生成绩从小到大排序  ClassSet{sortByScore()}
*/
import java.util.Arrays;

public class TestComparable {
    
    public static void main(String[] args) {
        //实例化4G班级
        ClassSet c = new ClassSet("4G", 4);
        //添加学生
        c.addStudent(new Student("李明", 90));
        c.addStudent(new Student("李浩", 80));
        c.addStudent(new Student("王涛", 95));
        c.addStudent(new Student("张胜", 70));

        //获得4G班级学生数组集合
        Student[] students = c.getStudents();
        //输出学生信息
        for (Student s : students) {
            if (s != null)
                System.out.println(s.getName() + "," + s.getMathScore());
        }

        System.out.println("\n根据学生成绩排序");
        Arrays.sort(students);
        for (Student s : students) {
            if (s != null)
                System.out.println(s.getName() + "," + s.getMathScore());
        }

    }
}

class ClassSet {
    
    private String className;//班级名称
    private int maxSize;//班级学生人数
    private int currentSize;//当前多少学生
    private Student[] students;//所有学生的数组

    public ClassSet(String className, int maxSize) {
        this.className = className;
        this.maxSize = maxSize;
        students = new Student[maxSize];
    }

    public Student[] getStudents() {
        return this.students;
    }

    //添加学生
    public void addStudent(Student s) {
        for (int i = 0; i < students.length; i++) {
            if (students[i] == null) {
                students[i] = s;
                currentSize++;
                break;
            }
        }
    }
}

class Student implements Comparable {
    private String name;//学生姓名
    private int mathScore;//数学成绩

    public Student(String name, int mathScore) {
        this.name = name;
        this.mathScore = mathScore;
    }

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getMathScore() {
        return this.mathScore;
    }

    public void setMathScore(int mathScore) {
        this.mathScore = mathScore;
    }

    /**
        实现Comparable 接口要复写 compareTo(T o) 方法
        如果从小到大排序
        大于         则返回 1
        小于         则返回 -1
        等于         则返回 0
        如果从大到小排序
        大于         则返回 -1
        小于         则返回 1
        等于         则返回 0
    */
    public int compareTo(Object obj) {
        if (obj instanceof Student) {
            Student s = (Student) obj;
            if (this.mathScore > s.getMathScore())
                return 1;
            if (this.mathScore < s.getMathScore())
                return -1;

        }
        return 0;
    }

}

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