Module [303] - Java Multi-Dimensional Arrays

This module should be shorter than usual but it will allow you to fullfill two objectives;

• First, it will supplement what we learned about java arrays by considering multi-dimensional arrays. The hands-on "Homework" will give you a somewhat advanced problem to work with that should help you understand the various things to keep in mind when working with higher-dimensionality arrays.
• Second, it will give us a bit more practice with harder CodingBat exercises on 1-dimensional arrays. Students often have difficulties getting a hold on arrays so do not hesitate to use the extra time in this module to book office hours time with your instructor or TAs.

Overall, this module should be a very good opportunity to prepare for the final and take the time to seek help while doing so.

There will be no wrap-up video for this module since the various programming skills we have been studying apply similarly to multi-dimensional arrays than 1-dimensional ones.

Module Learning Outcomes

In this module, you will develop further your programming skills as follows;

Tracing

Ability to read and trace Java programs leveraging 2 dimensional arrays.

Implementing

Ability to write Java programs leveraging 2 dimensional arrays.

Testing

Ability to develop tests for Java programs leveraging 2 dimensional arrays.

Debugging

Ability to troubleshoot Java programs leveraging 2 dimensional arrays.

Designing

Ability to design Java programs leveraging 2 dimensional arrays.

Let us create a new file named MyMatrix.java. It will feature the following method;

   /**
   *  Returns true if all elements of the matrix are in ascending order, false otherwise. 
   *  When determining if two consecutive elements are in order, we read them from the first row
   *  to the last row and, inside each row, from the first column to the last column.
   **/
   public static boolean isMatrixSorted(int[][] data){
      return true;   
   }

The above implementation always return true so you will have to rewrite it to do better than this.

In order to test this method, you will also write a main method in the same java file. Your main will repeatedly call isMatrixSorted on various matrices to test whether it is working or not. Here is what your main method must look like, just add more tests to it;

   public static void main(String[] args) {
      String[] msg = {  "Already sorted Matrix",
                        "Mixed up matrix" };
      boolean[] expected = {true, false};
      int[][] test0 = { {1,2,3,4,5}, {6,7,8,9,10}, {11,12,13,14,15} };
      int[][] test1 = { {5,3,2,1,4}, {9,8,6,7,10}, {13,12,14,15,11} };
      runTest(msg[0], isMatrixSorted(test0) == expected[0]);
      runTest(msg[1], isMatrixSorted(test1) == expected[1]);
   };

The runTest method is given to you below and must be part of your java file too;

  public static void runTest(String msg, boolean result){
    System.out.printf("Testing [%-30.30s]\t --> %s\n", msg, result?"shiny":"FAILED");
  }

The following exercises are from the Array-3 group from the JavaBat website. They are still focussed on 1-dimensional arrays but the programs we write are a bit more difficult to design, requiring multiple nested loops.