Question

问题： 如何从数组中查找min / max以及语法是什么样的？

（（编辑：开始处理它可能是什么样子（在这篇文章的底部），但我没有正确的语法））

想在我的主课程中创建一个方法，以便从一系列学生中找到具有最佳和最差成绩（和打印）的学生，而不确定语法在数组中的外观。

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;
}
}

students.txt

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

以下是输出的外观（所以我现在错过了最后两行）：

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

此处编辑比在评论中发布更容易。我更新了帖子，使其更清楚我要问的是什么。

这是我到目前为止找到最大值的内容，但我仍然对确切的内容感到困惑。

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

要获得最高和最低等级，只需循环遍历数组中的所有项目将2个变量保持为最高和最低。

int highest = 0;
int lowest = 100;
Student high = arrStudents[0];
Student low = arrStudents[0];

for (int index = 0; index < arrStudents.length; index++)
{
    if (arrStudents[index].getGrade() > highest)
    {
         highest = arrStudents[index].getGrade();
         high = arrStudents[index];
    }
    else if (arrStudents[index].getGrade() < lowest)
    {
         lowest = arrStudents[index].getGrade();
         low = arrStudents[index];
    }
}
System.out.println("Student with the highest grade: " + high);
System.out.println("Student with the lowest grade: " + low);

然后按照您喜欢的方式打印出来。希望这会有所帮助。

Answer 2

以下内容如何：

// 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，您应该考虑使用Collections而不是plain数组。特别是因为你事先并不真正了解学生人数。

以上代码可以像这样重写：

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
}

或更短的使用java 8 lambdas：

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
}

Answer 3

您需要遍历数组并保留max和min的值

Student[] arrStudents = new Student[7];
Student max=arrStudents[0];
Student min=arrstudents[1];
for (int i=0; i < arrStudents.length(); i++){
   if arrStudents[i].getGrade() >max.getGrade(){
      max = arrStudents[i];
   }
   else if arrStudents[i].getGrade() <min.getGrade(){
      min =arrStudents[i];
   }
}

Java - 使用数组查找/打印最小/最大值？

3 个答案: