Value calling outside while loop in java

Question

I have two data file. Data are double type. File one consist of 3 column and several Rows and File two consist of 4 Column and Several row. I read data from both file separately in one Java program and the Column one data of File1 are matched with the Column one data of File2 then a message will display that data are matched else data are not match. My code is like that

import java.io.File;
import java.util.Scanner;

public class F1 {
public static void main(String args[])throws Exception{
    Scanner Y =new Scanner(new File("C:\\R5_M.txt"));
    Scanner X =new Scanner(new File("C:\\R5_O.txt"));
    double a=0.0,b=0.0,c,d=0.0,e=0.0,f,g,h;
    if(a==d) {
        while (X.hasNext()) {
            a = X.nextDouble();
            b = X.nextDouble();

            c = X.nextDouble();
        }


        while (Y.hasNext()) {
            d = Y.nextDouble();
            e = Y.nextDouble();

            f = Y.nextDouble();
            g = Y.nextDouble();

        }

        System.out.println("They are matched");
    }
 else{
        System.out.println("Not Matched");
    }

}

}

It's output is They are matched for only one time. But it should write output equal to number of rows. If I have 10 Rows in both data files and 6 data are matched and 4 are not matched then I get a output They are matched for 6 times and Not Matched for 4 times.

One obvious reason is both while loops are end within there scope.So the value that change for a,b,c,d,e,f,g are remain in the scope or should I say they are overwrite in each iteration and if I call a and d outside while loop then it returns only the last value in this case 10th value. So where should I write down the if statement to compare each value?

Answer 1

You need to do like this

 public static void main(String args[])throws Exception{
        Scanner Y =new Scanner(new File("C:\\R5_M.txt"));
        Scanner X =new Scanner(new File("C:\\R5_O.txt"));
        double a=0.0,b=0.0,c,d=0.0,e=0.0,f,g,h;
        while(X.hasNext() && Y.hasNext()){
                a = X.nextDouble();
                b = X.nextDouble();

                c = X.nextDouble();

                d = Y.nextDouble();
                e = Y.nextDouble();

                f = Y.nextDouble();
                g = Y.nextDouble();

          if(a==d) {
            System.out.println("They are matched");
              }
          else{
            System.out.println("Not Matched");
           }
     }

Answer 2

One efficient method is to use a map to store each entry from both files and then compare the two:

import java.io.File;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) throws Exception {

        Scanner Y = new Scanner(new File("C:\\R5_M.txt"));
        Scanner X = new Scanner(new File("C:\\R5_O.txt"));
        double a = 0.0, b = 0.0, c, d = 0.0, e = 0.0, f, g, h;

        // Create a map to hold the values from each file
        HashMap<String, Double> yList = new HashMap<>();
        HashMap<String, Double> xList = new HashMap<>();

        // Read in the data from both files
        while (Y.hasNext()) {
            // This will place the values into the HashMap. The first value is whatever "key"
            // you want to use, the second is the value itself.
            yList.put("a", Y.nextDouble());
            yList.put("b", Y.nextDouble());
            yList.put("c", Y.nextDouble());
        }

        while (X.hasNext()) {
            xList.put("a", X.nextDouble());
            xList.put("b", X.nextDouble());
            xList.put("c", X.nextDouble());
        }

        // Now, you can compare values in both maps
        // The HashMap has a list called entrySet that allows you to iterate over all
        // of the entries in the list
        for (Map.Entry<String, Double> entry : yList.entrySet()) {
            // This will check if the current entry's key/value pair matches the identical
            // key/value pair in the xList map.
            if (entry.getValue() == xList.get(entry.getKey()).doubleValue()) {
                System.out.println(entry.getKey() + " matches!");
            } else {
                System.out.println(entry.getKey() + " does NOT match!");
            }
        }

    }
}

This can be adapted to read an unknown number of entries from each file as well.