Java 数组和引用

Question

作为我学校类(class)的一部分，我们正在研究一些 CodeHS Java。我遇到了一个问题:

Taking our Student and Classroom example from earlier, you should fill in the method getMostImprovedStudent, as well as the method getExamRange. The most improved student is the one with the largest exam score range.

To compute the exam score range, you must subtract the minimum exam score from the maximum exam score.

For example, if the exam scores were 90, 75, and 84, the range would be 90 - 75 = 15.

这是我添加方法 getExamRange() 的 Student 类。

import java.util.*;

public class Student
{
    private static final int NUM_EXAMS = 4;
    
    private String firstName;
    private String lastName;
    private int gradeLevel;
    private double gpa;
    
    private int[] exams;
    private int numExamsTaken;
    public static int[] examRange = new int[Classroom.numStudentsAdded];
    private int i = 0;

    /**
     * This is a constructor.  A constructor is a method
     * that creates an object -- it creates an instance
     * of the class. What that means is it takes the input
     * parameters and sets the instance variables (or fields)
     * to the proper values.
     * 
     * Check out StudentTester.java for an example of how to use
     * this constructor. 
     */
    public Student(String fName, String lName, int grade)
    {
        firstName = fName;
        lastName = lName;
        gradeLevel = grade;
        exams = new int[NUM_EXAMS];
        numExamsTaken = 0;
    }
    
    public int getExamRange()
    {
        Arrays.sort(exams);
        examRange[i] = exams[exams.length-1] - exams[0];
        i++;
        return exams[exams.length-1] - exams[0];
    }
    
    public String getName()
    {
        return firstName + " " + lastName;
    }
    
    public void addExamScore(int score)
    {
        exams[numExamsTaken] = score;
        numExamsTaken++;
    }
    
    // This is a setter method to set the GPA for the Student.
    public void setGPA(double theGPA)
    {
        gpa = theGPA;
    }
    
    /**
     * This is a toString for the Student class. It returns a String
     * representation of the object, which includes the fields
     * in that object.
     */
    public String toString()
    {
        return firstName + " " + lastName + " is in grade: " + gradeLevel;
    }
}

这是我在其中添加方法 getMostImprovedStudent() 的 Classroom 类。

import java.util.*;

public class Classroom
{
    Student[] students;
    static int numStudentsAdded;
    
    public Classroom(int numStudents)
    {
        students = new Student[numStudents];
        numStudentsAdded = 0;
    }
    
    public Student getMostImprovedStudent()
    {
        Arrays.sort(Student.examRange);
        //return Student.examRange[0];
    }
    
    public void addStudent(Student s)
    {
        students[numStudentsAdded] = s;
        numStudentsAdded++;
    }
    
    public void printStudents()
    {
        for(int i = 0; i < numStudentsAdded; i++)
        {
            System.out.println(students[i]);
        }
    }
}

我可以通过对 exams 数组进行排序然后从最大的减去最小的来获得考试范围，但是一旦我这样做，我如何找到考试范围最大的学生并返回它？

Answer 1

这样做的方法是遍历 students，并用一个变量来保存分数差异最大的学生和进步最快的学生:

public Student getMostImprovedStudent()
{
    Student mostImproved = students[0];
    int biggest = student[i].getExamRange();
    for(int i = 1; i < students.length; i++) {
        if(students[i].getExamRange() > biggest) {
            mostImproved = students[i];
            biggest = students[i].getExamRange();
        }
    }
    return mostImproved;
}

但是 Java 8+ 我们可以做到:

public Student getMostImprovedStudent()
{
    return Arrays.stream(students)
                 .max(Comparator.comparing(Student::getExamRange))
                 .get();                     
}

假设 students 不为空