Java 常用类库 之 比较接口 Comparator

Posted 2020-11-19 verejava

http://www.verejava.com/?id=169931036202101

/**
    知识点： 比较类 Comparator

    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;
import java.util.Comparator;
public class TestComparator
{
    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("
根据学生成绩升序排序");
        Arrays.sort(students,new StudentAscComparator());
        for(Student s:students)
        {
            if(s!=null)
                System.out.println(s.getName()+","+s.getMathScore());
        }

        System.out.println("
根据学生成绩降序排序");
        Arrays.sort(students,new StudentDescComparator());
        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 
{
    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;
    }
}
/**
    学生升序排列
*/
class StudentAscComparator implements Comparator
{
    public int compare(Object o1,Object o2)
    {
        if((o1 instanceof Student)&&(o2 instanceof Student))
        {   
            Student s1=(Student)o1;
            Student s2=(Student)o2;
            if(s1.getMathScore()>s2.getMathScore())
                return 1;
            if(s1.getMathScore()<s2.getMathScore())
                return -1;
        }
        return 0;
    }
}
/**
    学生降序排列
*/
class StudentDescComparator implements Comparator
{
    public int compare(Object o1,Object o2)
    {
        if((o1 instanceof Student)&&(o2 instanceof Student))
        {   
            Student s1=(Student)o1;
            Student s2=(Student)o2;
            if(s1.getMathScore()>s2.getMathScore())
                return -1;
            if(s1.getMathScore()<s2.getMathScore())
                return 1;
        }
        return 0;
    }
}

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