4.d, Java - rextester

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//'main' method must be in a class 'Rextester'.
//openjdk version '11.0.5' 
//  Razak-7051
 import java.util.*;
import java.lang.*;

class Rextester
{  
    public static void main(String args[])
    {
          int m, n, p, q, sum = 0, c, d, k; 
    Scanner in = new Scanner(System.in);
    System.out.println("Enter the number of rows and columns of first matrix");
    m = in.nextInt();
    n = in.nextInt(); 
    int first[][] = new int[m][n]; 
    System.out.println("Enter elements of first matrix"); 
    for (c = 0; c < m; c++)
      for (d = 0; d < n; d++)
        first[c][d] = in.nextInt();
     System.out.println("Enter the number of rows and columns of second matrix");
    p = in.nextInt();
    q = in.nextInt(); 
    if (n != p)
      System.out.println("The matrices can't be multiplied with each other.");
    else{
      int second[][] = new int[p][q];
      int multiply[][] = new int[m][q]; 
      System.out.println("Enter elements of second matrix"); 
      for (c = 0; c < p; c++)
        for (d = 0; d < q; d++)
          second[c][d] = in.nextInt(); 
      for (c = 0; c < m; c++) {
        for (d = 0; d < q; d++) {
          for (k = 0; k < p; k++)
            sum = sum + first[c][k]*second[k][d]; 
          multiply[c][d] = sum;
          sum = 0;
        }
      } 
      System.out.println("Product of the matrices:"); 
      for (c = 0; c < m; c++) {
        for (d = 0; d < q; d++)
          System.out.print(multiply[c][d]+"\t"); 
        System.out.print("\n");
      }
    }
  }    
}

[ - ] Show input
Compilation time: 1.12 sec, absolute running time: 0.3 sec, cpu time: 0.25 sec, memory peak: 38 Mb, absolute service time: 1,54 sec