LinTool and other Programming Issues

Step 4: Go a bit further with LinTool

Let's start down the road to implementation by understanding how to use LinTool:

• The main idea is this: LinTool is an abstract class that defines a number of methods that you will implement. Each of these methods is a linear algebra computation.

• For example, examine the method that adds two real numbers in LinTool. It takes in two real numbers (as double's) and should return the sum. Easy to implement, right?

• Let's implement just that method alone and subject the implementation to testing.

• We will call our implementation AliceLinTool.java for our example user called Alice. You will of course use your username instead. Meanwhile, let's examine the code:

  import edu.gwu.lintool.*;
  
  public class AliceLinTool extends LinToolEmpty {
  
      // We'll now override the method that adds two real numbers.
      public double add (double a, double b)
      {
  	double c = a + b;
  	return c;
      }
  
  }
      

  Note the following:
  • We need to import the lintool package, at the top.
  • The method signature (first line) is exactly the same as described in the documenation of LinTool.
  • Only that one method was implemented inspite of the fact that LinTool has many, many methods. How is this possible? It is made possible because LinTool provides a default so-called "empty" implementation that implements all the methods. The default implementation does nothing at all. Each time you implement a method, your implementation overrides the default implementation.

• Now download and save both AliceLinTool.java and a special test file called TestLinTool.java in the testdir you created a while back.

• Let's examine TestLinTool.java:

  import edu.gwu.lintool.*;
  
  public class TestLinTool {
  
      public static void main (String[] argv)
      {
  	AliceLinTool alice = new AliceLinTool ();
  	LinTest.testRealNumberAdd (alice);
      }
  
  }
      

  Observe the following:
  • This is a simple test file that creates an instance of Alice's implementation and subjects it to a test.
  • Again, the import statement is needed at the top.
  • There is a mysterious method called testRealNumberAdd() that takes Alice's implementation and subjects it to a test.

• Compile and run TestLinTool.java, and you'll see that it passes the test.

• This is essentially the manner in which you will implement and test your code. First you will implement a couple of methods from LinTool, then you will test your implementation.

• To see a complete list of tests, examine the code in AllLinToolTests.java.

• By the end of the semester, you will have written a linear algebra toolkit.