从输入文件中读取然后按升序打印排序的名字

Question

import static java.lang.System.*;
import java.io.FileNotFoundException;
import java.util.*;
import java.io.*;
import java.math.*;
import java.text.*;
import java.util.ArrayList;
import java.util.Arrays;
import static java.util.Comparator.comparing;


public class Main
{
  public static void main (String[]args) throws IOException
  {
      
    PrintWriter pw1 = new PrintWriter ("input.txt");
      pw1.println ("Mickey Mouse CS 98.7 67.8 23.5");
      pw1.println ("Minnie Mouse ENG 45.6 98.3 94.7");
      pw1.println ("Donald Duck NET 56.8 74.2 78.4");
      pw1.println ("Bob Builder CS 78.5 89.4 82.5");
      pw1.println ("Snow White MAT 56.6 32.4 56.6");
      pw1.println ("Hellen Keller CHEM 78.8 23.1 99.6");
      pw1.println ("Daffy Duck ENG 67.4 55.5 89.5");
      pw1.println ("Fred Flinstone MAT 45.3 87.4 38.9");
      pw1.println ("Daffy Duck CS 76.5 22.2 88.5");
      pw1.println ("Bugs Bunny NET 68.4 89.7 95.6");
      pw1.println ("Winnie Pooh CHEM 77.5 89.4 98.2");
      pw1.close ();
File q=new File("input.txt");
generateStatsFile(q);
}

public static void generateStatsFile (File inputfile) throws IOException{
    Scanner in=new Scanner (inputfile);
    ArrayList<student> ss=new ArrayList<student>(4);
    ArrayList<student>s=new ArrayList<student>();
     String []fname=new String[s.size()];
    while (in.hasNext()){
        student we=new student(in.next (), in.next (), in.next(),in.nextFloat (),
        in.nextFloat (), in.nextFloat ());
        ss.add(we);
        
        
      
        //Collections.sort(s);
        
    }
        FileWriter of=new FileWriter("out.txt");
    PrintWriter output=new PrintWriter(of);
    while(in.hasNext()){
        student ee=new student(in.next (), in.next (), in.next(),in.nextFloat (),
        in.nextFloat (), in.nextFloat ());
    s.add(ee);    
        
        
    }
    
    //Collections.sort(s, comparing(ee::getfname));
/*s.sort((o1,o2)
-> o1.getfname().compareTo(
                          o2.getfname()));*/
                          
  // Comparator<student> compareByName = (student o1, student o2) ->
                //  o1.getfname().compareTo( o2.getfname() );
    
//Collections.sort(s,compareByName);


    for (student he:ss)
    {
        
        
        
       
        output.printf("%s %s %.1f%n",he.getfname(),he.getlname(),he.getavg(he.getg1(),he.getg2(),he.getg3()));


        
    }
 String []cnmb=(s.toArray(new String[s.size()])); 
 Arrays.sort(cnmb);
output.print(cnmb);    
    
    
   /* for(int i=0;i<s.size();i++){
    System.out.println(Arrays.toString(s.toArray()));    
        
        
    }*/
    for(String ha:cnmb){
    out.println(ha);
    
} 


/*for (String ha:s){
    
    String [] fn=new String[s.size()];
   for(int i=0;i<s.size();i++){
    fn[i]=ha.getfname();
    
}*/
//out.print(fn); 
    
    
    //out.print(s);
    

         
    in.close();
    output.close();
  
  
 
}
}

你好所以基本上这个方法应该写入一个 output 文件 a.平均成绩和字母 b.名字按升序排序

第一个选项奏效了。 但是，我为选项 b 编写的代码无法正常工作，它要么不打印任何内容，要么只是在文件中打印类似[Ljava.lang.String;@880ec60的内容，有人可以帮忙吗？我知道代码真的很乱，因为我放了一个在不同的代码行之前有很多注释符号，但也许其中一些应该有用我只是没有让完整的代码正常工作。

public class student implements Comparable<student>{
       
private String fname;
private String lname;
private String major;
private float grades1;    
private float grades2; 
private float grades3;   

public String getfname() {return fname;}
public String getlname() {return lname;}
private String getmajor() {return major;}
public float getg1() {return grades1;}
public float getg2() {return grades2;}
public float getg3() {return grades3;}

@Override
    public int compareTo(student e) {
        return this.getfname().compareTo(e.getfname());
    }

public student(){
    
    
    
}
public String fname(){
return fname;    
    
    
    
}
public student(String f){
fname=f;    
    
    
}
public student(String f,String l,String m,float g1,float g2, float g3)  {  
    fname=f;
    lname=l;
    major=m;
    grades1=g1;
    grades2=g2;
    grades3=g3;
     
}
public student(String f,String l,float g1,float g2, float g3)  {  
    fname=f;
    lname=l;
    grades1=g1;
    grades2=g2;
    grades3=g3;
     
}
public float getavg (float g1,float g2,float g3){
grades1=g1;
grades2=g2;
grades3=g3;

float avg=(g1+g2+g3)/3;
    
    
return avg;   
}

public String [] sortfname(String fname){
String [] f=new String[0];


return f;

}

Answer 1

您似乎使这比需要的复杂得多。

您的student class 已经实现了Comparable接口，因此您不需要 class Arrays ，您可以使用 class java.util.Collections中的方法排序。

此外， class java.io.PrintWriter具有一个采用String参数的构造函数，因此无需创建FileWriter 。

请注意，文件需要关闭，因此，在下面的代码中，我使用了 try-with-resources 。

出于您的程序的目的，您只需要一个 class student的构造函数。

为了获得正确的 output，您需要重写方法toString 。

方法getAverage不应有任何参数。 它应该使用应该在 class 构造函数中初始化的 class 成员grades1 、 grades2和grades3 。

您在问题中提到了字母等级，但我在您的代码中看不到任何处理该问题的内容，因此我将方法getLetterGrade添加到 class student 。

在下面的代码中，我创建了一个student对象List ——而不是将它们写入文件，然后通过读取文件重新创建List 。

最后，您应该考虑使用java 命名约定。 根据这些约定，名称 class 在以下代码中更改为Student 。

import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Student implements Comparable<Student> {
    private String fname;
    private String lname;
    private String major;
    private float grades1;
    private float grades2;
    private float grades3;

    public Student(String fname,
                   String lname,
                   String major,
                   float grades1,
                   float grades2,
                   float grades3) {
        this.fname = fname;
        this.lname = lname;
        this.major = major;
        this.grades1 = grades1;
        this.grades2 = grades2;
        this.grades3 = grades3;
    }

    @Override
    public int compareTo(Student o) {
        return fname.compareTo(o.fname);
    }

    public float getAverage() {
        float total = grades1 + grades2 + grades3;
        return total / 3;
    }

    public char getLetterGrade() {
        char letter;
        float average = getAverage();
        if (average >= 90.0f  &&  average <= 100.0f) {
            letter = 'A';
        }
        else if (average >= 80.0f  &&  average < 90.0f) {
            letter = 'B';
        }
        else if (average >= 70.0f  &&  average < 80.0f) {
            letter = 'C';
        }
        else if (average >= 60.0f  &&  average < 70.0f) {
            letter = 'D';
        }
        else if (average >= 0.0f  &&  average < 60.0f) {
            letter = 'F';
        }
        else {
            throw new RuntimeException("Invalid average: " + average);
        }
        return letter;
    }

    public String toString() {
        return String.format("%s %s %s %.2f %c", fname, lname, major, getAverage(), getLetterGrade());
    }

    public static void main(String[] args) {
        List<Student> list = new ArrayList<>();
        list.add(new Student("Mickey", "Mouse", "CS", 98.7f, 67.8f, 23.5f));
        list.add(new Student("Minnie", "Mouse", "ENG", 45.6f, 98.3f, 94.7f));
        list.add(new Student("Donald", "Duck", "NET", 56.8f, 74.2f, 78.4f));
        list.add(new Student("Bob", "Builder", "CS", 78.5f, 89.4f, 82.5f));
        list.add(new Student("Snow", "White", "MAT", 56.6f, 32.4f, 56.6f));
        list.add(new Student("Hellen", "Keller", "CHEM", 78.8f, 23.1f, 99.6f));
        list.add(new Student("Daffy", "Duck", "ENG", 67.4f, 55.5f, 89.5f));
        list.add(new Student("Fred", "Flinstone", "MAT", 45.3f, 87.4f, 38.9f));
        list.add(new Student("Daisy", "Duck", "CS", 76.5f, 22.2f, 88.5f));
        list.add(new Student("Bugs", "Bunny", "NET", 68.4f, 89.7f, 95.6f));
        list.add(new Student("Winnie", "Pooh", "CHEM", 77.5f, 89.4f, 98.2f));
        Collections.sort(list);
        try (PrintWriter pw = new PrintWriter("out.txt")) {
            for (Student learner : list) {
                pw.println(learner);
            }
        }
        catch (IOException xIo) {
            xIo.printStackTrace();
        }
    }
}

以下是文件out.txt的内容：

Bob Builder CS 83.47 B
Bugs Bunny NET 84.57 B
Daffy Duck ENG 70.80 C
Daisy Duck CS 62.40 D
Donald Duck NET 69.80 D
Fred Flinstone MAT 57.20 F
Hellen Keller CHEM 67.17 D
Mickey Mouse CS 63.33 D
Minnie Mouse ENG 79.53 C
Snow White MAT 48.53 F
Winnie Pooh CHEM 88.37 B