Java - 使用数组查找/打印最小值/最大值？

Question

问题: 我如何从数组中查找最小值/最大值以及语法是什么样的？

((编辑:开始研究它可能的样子(在这篇文章的底部)，但我没有得到正确的语法))

想在我的主课中创建一个方法，从一组学生中找到成绩最好和最差的学生(并打印)，不确定数组的语法如何。

Main.java

import java.util.*;
import java.io.*;

public class Main
{
private static int i=0;

public static void main (String[] args) throws IOException
{                        
    Student[] arrStudents = new Student[7];

    Scanner fileInput = new Scanner(new File("students.txt")); 

    while (fileInput.hasNext())
    {             
        String firstName = fileInput.next();
        String lastName = fileInput.next();
        int grade = fileInput.nextInt();

        arrStudents[i] = new Student(firstName, lastName, grade);
        i++;
    }  

    getExcellentStudents(arrStudents);
    getOKStudents(arrStudents);
    getFailStudents(arrStudents);
    System.out.println(); 
    System.out.println("Total Number of Students: " + arrStudents.length);
}

public static void getExcellentStudents(Student[] arrStudents) throws IOException {               
    System.out.println("Excellent Students: ");
    for(int i = 0; i < arrStudents.length; i++) {
       int grade = arrStudents[i].getGrade();

        if (grade > 89) {                    
            System.out.println(arrStudents[i]);
       }
    }
    System.out.println();
}


public static void getOKStudents(Student[] arrStudents) throws IOException {               
    System.out.println("OK Students: ");
    for(int i = 0; i < arrStudents.length; i++) {
       int grade = arrStudents[i].getGrade();

        if (grade > 60 && grade < 90) {
            System.out.println(arrStudents[i]);
       }
    }
    System.out.println();
}


public static void getFailStudents(Student[] arrStudents) throws IOException {     
    System.out.println("Failure Students: ");
    for(int i = 0; i < arrStudents.length; i++) {
       int grade = arrStudents[i].getGrade();

        if (grade < 61) {
            System.out.println(arrStudents[i]);
       }
    }
    System.out.println();
}

Student.java

public class Student {
private String firstName, lastName;
private int grade;

public Student (String firstName, String lastName, int grade)
{
    this.firstName = firstName;
    this.lastName = lastName;
    this.grade = grade;
}

public String toString()
{
    return firstName + " " + lastName + " " + grade;
}

public int getGrade()
{
    return grade;
}
}

学生.txt

John Smith 90
Barack Obama 95
Al Clark 80
Sue Taylor 55
Ann Miller 75
George Bush 58
John Miller 65

输出应如下所示(所以我现在缺少最后两行):

Excellent Students: 
John Smith 90
Barack Obama 95

OK Students: 
Al Clark 80
Ann Miller 75
John Miller 65

Failure Students: 
Sue Taylor 55
George Bush 58


Total Number of Students: 7
Student With Highest Grade: Barack Obama 95
Student With Lowest Grade: Sue Taylor 55

在这里编辑比在评论中发布更容易。我更新了这篇文章，使其更清楚地表达了我的要求。

这是迄今为止我找到最大值的方法，但我仍然对到底什么去了哪里感到困惑。

public void outputMaxMin(Student[] arrStudents) throws IOException {       
Student bestStudent;
Student worstStudent;
student = new Student();

for (int i = 0; i < arrStudents.length; i++) {
  int grade = arrStudents[i].getGrade();
  if (bestStudent == null && worstStudent == null) {
    bestStudent = student;
    worstStudent = student;
    continue; 
  } 

  if (grade > bestStudent.grade){
    bestStudent = student;
  }
  if (grade < worstStudent.grade){
    worstStudent = student;
  }

}    
}

Answer 1

以下怎么样:

// assume students.length > 0
static void printMinMax(Student[] students) {
  Student min = students[0];
  Student max = students[0];

  for (Student student: students) {
    if (student.getGrade() > max.getGrade())
      max = student;
    if (student.getGrade() < min.getGrade())
      min = student;
  }

  System.out.println("Best student: " + max);
  System.out.println("Worst student: "+ min);
}

另一方面，您应该真正考虑使用集合而不是普通数组。 特别是因为您事先并不真正知道学生的数量。

上面的代码可以这样重写:

static void printMinMax(List<Student> students) {
  Comparator<Student> comparator = new Comparator<>() {
    @Override public int compare(Student s1, Student s2) {
      return s1.getGrade() - s2.getGrade();
    }
  };
  Student max = Collections.max(students, comparator);
  Student min = Collections.min(students, comparator);

  // print stuff
}

使用 java 8 lambda 或更短:

static void printMinMax(List<Student> students) {
  Comparator<Student> comparator = (s1, s2) -> s1.getGrade() - s2.getGrade();

  Student max = Collections.max(students, comparator);
  Student min = Collections.min(students, comparator);

  // print stuff
}