Functional Decomposition

1. Functional Decomposition

2. At the beginning of this unit we discussed how most of your programs have been written like this: public class BigProgram { public static void main (String [ ] args) { statement; statement; statement; statement; statement; statement; statement; statement; statement; statement; statement; statement; } }

3. There are problems with writing all of the code in the main method: • Programs can get very long. The longer they are the harder they are to manage. • Human beings are not computers. We don’t see information as a whole like a computer.

4. Human beings “chunk” data. For example, try memorizing the following number: 7743125039

5. What is that number?

6. Now, let’s divide that number into chunks: 774 – 312 - 5039 • Try memorizing that number now.

7. What is that number?

8. Chances are you were able to memorize it that time because you “chunked” the data. • Programmers do the same thing when they design and develop programs. • Functional Decomposition: • The process of breaking a problem into smaller pieces.

9. Functional Decomposition has advantages in programming: • The best way to solve a complex problem is to break it down into smaller problems. • Using methods, specific parts of a problem can be written at one time. You don’t have to worry about the whole program. • Methods allow the program to be broken up so multiple people can work on ONE program.

10. main method • Again, this is what a program looks like when it is broken up into smaller methods: public class DividedProgram { public static void main (String [ ] args) { statement; statement; } public static void method2( ) { statement; statement; } public static void method3( ) { statement; statement; } public static void method4( ) { statement; statement; } } method 2 method 3 method 4

11. Here is an example of a main method that uses functional decomposition to call other methods: public static void main(String[] args) throws IOException { int intNumDays = 30; // Number of days of sales String strFileName; // The name of the file to open double dblTotalSales; // Total sales for period double dblAverageSales; // Average daily sales // Get the name of the file. strFileName = getFileName(); // Get the total sales from the file. dblTotalSales = getTotalSales(strFileName); // Calculate the average. dblAverageSales = calcAverageSales(dblTotalSales, intNumDays); // Display the total and average. displayResults(dblTotalSales, dblAverageSales); System.exit(0); }