Lab: Recursion on NaturalNumber – Static Methods

Objective

In this lab you will practice recursion on NaturalNumbers by implementing the decrement and printWithCommas static methods.

Setup

Follow these steps to set up a project for this lab.

1. Create a new Eclipse project by copying ProjectTemplate. Name the new project RecursionOnNaturalNumber1.
2. Open the src folder of this project and then open (default package). As a starting point you can use any of the Java files. Rename it NaturalNumberStaticOps and delete the other files from the project.
3. Follow the link to NaturalNumberStaticOps.java, select all the code on that page (click and hold the left mouse button at the start of the program and drag the mouse to the end of the program) and copy it to the clipboard (right-click the mouse on the selection and choose Copy from the contextual pop-up menu), then come back to this page and continue with these instructions.
4. Finally in Eclipse, open the NaturalNumberStaticOps.java file; select all the code in the editor, right-click on it and select Paste from the contextual pop-up menu to replace the existing code with the code you copied in the previous step. Save your file.

Method

1. Complete the body of the decrement static method using only the NaturalNumberKernel methods (multiplyBy10, divideBy10, and isZero). The code for increment is provided as an example of a recursive method on NaturalNumber.
2. Run the program and test your implementation of decrement.
3. Complete the body of the printWithCommas static method. This method outputs the given NaturalNumber to an output stream, inserting a comma before every group of three digits (from right to left). So the number 12345678 would be printed as 12,345,678. For this method you can use any of the NaturalNumber methods. Note that the contract for this method states (implicitly) that the value of the given NaturalNumber must be restored so that the outgoing value of n is the same as the incoming value.
4. Run the program and test your implementation of printWithCommas.

Additional Activities

1. Complete the body of the toStringWithCommas static method. This method is similar to printWithCommas, except that instead of printing the number with commas to an output stream, it returns a String representation of the number with commas.
2. Run the program and test your implementation of toStringWithCommas.