// exj4.java   example file  iteration, loops

public class exj4  // class name same as file name
{
  public exj4() // constructor same as class name
  {

    System.out.println("exj4.java running");

    int i;             // declare loop variable
    int mat[][] = {{1,2,3},{2,3,4},{3,4,5},{4,5,6}}; // 4 by 3 matrix
    int sum = 0;

    for(i=0; i<4; i++)  // columns of mat
    {                 // the } could be at end of previous line   
      for(int j=0; j<3; j++) //  j only exists inside loop
      {
        sum += mat[i][j];
      } // end j  optional comment
    } // end i  optional comment
    System.out.println("sum="+sum);

    for(i=2; i<=10; i=i+2)
    {
      System.out.println("i="+i); // even numbers
    }
  } // end constructor exj4       // optional comment
    
  public static void main (String[] args)
  {
    new exj4();
  }
} // end class exj4    optional comment