从两个哈希键中找到平均值

Question

import java.io.*;
import java.util.HashMap;
import java.util.Scanner;

public class orde {
public static void main(String args[]) throws IOException {
  Scanner c1=new Scanner(new FileReader(new File("students.txt")));
  Scanner c2=new Scanner(new FileReader(new File("course1.txt")));
  Scanner c3=new Scanner(new FileReader(new File("course2.txt")));
  HashMap<String,String> M1=new HashMap<String,String>();
  HashMap<String,String> M2=new HashMap<String,String>();
  HashMap<String,String> M3=new HashMap<String,String>();
  add(c1,M1);
  add(c2,M2);
  add(c3,M3);

  for(String key:M1.keySet()) {
    if(M2.containsKey(key))
      System.out.println(key+" "+M1.get(key)+" "+ "course1:"+ " " + M2.get(key)+ " " +  "course2:"+ " " + M3.get(key));
  }
}
private static void add(Scanner c1,HashMap<String, String> M) {
  while(c1.hasNext()) {
    String S[]=c1.nextLine().split(" ");
    M.put(S[0],S[1]);
  }
}
}

输出是这样的：

25212 Greg IR101: 70.5 IR102: 72.5
25954 Betty IR101: 70.2 IR102: 63.4
25321 Elsie IR101: 51.5 IR102: 45.6
25654 Chris IR101: 58.6 IR102: 35.1

基本上我使用散列连接将三个文件连接在一起，一个包含学生 ID 和姓名，课程 1 包含模块 1 的标记，课程 2 包含模块 2 的标记，但我尝试计算两个标记（M2 和 M3）的平均值时遇到问题，例如完成后应该如下所示：

 25212 Greg IR101: 70.5 IR102: 72.5 Average: 71.5
 25954 Betty IR101: 70.2 IR102: 63.4 Average: 66.8

Answer 1

由于您的值是字符串，因此您可以将它们解析为双精度值：

String myString = "70.5";
double x = Double.parseDouble(myString);

现在你可以用它来计算平均值

String s1 = "70.5";
String s2 = "72.5";

double m = (Double.parseDouble(s1)+Double.parseDouble(s2))/2d;
System.out.println(m);

请注意，如果您尝试解析的值不是数字，则可能会出错
即

String myString="test";
double x = Double.parseDouble(myString); // error

对于你的情况，一个小例子：

public static void main(String[] args){

      HashMap<String,String> M1=new HashMap<String,String>();
      HashMap<String,String> M2=new HashMap<String,String>();
      HashMap<String,String> M3=new HashMap<String,String>();
      M1.put("222", "Greg");
      M2.put("222","70.5");
      M3.put("222", "72.5");

      for(String key:M1.keySet()) {
        if(M2.containsKey(key)){
            double average = (Double.parseDouble(M2.get(key))+Double.parseDouble(M3.get(key)))/2d;
            System.out.println(key+" "+M1.get(key)+" "+ "course1:"+ " " + M2.get(key)+ " " +  "course2:"+ " " + M3.get(key)+" average:"+average);
        }
    }

}

从两个哈希键中找到平均值

Finding the mean from two hash keys

java

hash

average

mean