Lab 7: Methods

For the TA
- In this lab, students must write 2 static methods that print figures using letters
- The lab assignment is self-explanatory and your job is to assist students (show them the answers) when they have questions.
Lab goals
- In this lab you will write one Java class that provides useful methods for creating text based drawings.
  Please, make sure that you have added the honor code statement at the top of your Java file:
  The deadline for completing this lab assignment is midnight, today.
Preparation: Create your ~/cs170/lab7/, and copy files
- Copy-and-paste these terminal commands:
  In this lab, we will use gedit and javac (not BlueJ !).
  (You could use BlueJ, but you must figure out how to compile and run the program on your own.)

Overview of the provided methods

Look at the program Sample.java with gedit:

You are provided with the following method:

indentCharLine(i, c, n):

This method will first print i spaces (i.e., indents i positions)
Then, it prints the character c (given as input of the method), n times (n is also an input parameter)
Finally, it prints NEWLINE (to end the current line)

Example:

indentCharLine(4, 'A', 6) will print: ____AAAAAA indentCharLine(6, 'X', 3) will print: ______AAA (I use _ to represent a BLANK SPACE)

The Sample.java program contains the printSquare() method that shows you how to use the method indentCharLine() to draw a square:

/* =============================================================== How to use indentCharLine() to draw a square: printSquare(i, c, n): Prints out a square - indented by i spaces - of height and width equal to n, using character c =============================================================== */ public static void printSquare(int i, char c, int n) { int row, col; /* ----------------------------------------- Print n rows of character c of width n ----------------------------------------- */ for ( row = 0; row < n; row++ ) { indentCharLine(i, c, n); } }

The main() method in Sample.java invokes printSquare() to draw 2 squares:

public static void main(String[] args) { printSquare(4, 'O', 2); System.out.println(); printSquare(4, 'X', 3); }

You can see the result by compiling and executing the program Sample.java:

Lab Assignment - Part 1: write the printColumn() method

Edit the AsciiArt.java program that is provided for this lab:

Complete the printColumn() method:

/* ================================================================ TODO: write this method printColumn(i, w, h, c): Prints out a column - indented by i positions- of width w and heigh h. The character used to print is passed as a parameter to the method by the variable c. *** NOTE: This method uses the "indentCharLine" method inside. ================================================================ */ public static void printColumn(int i, int w, int h, char c) { ... }

After completing the printColumn() method, you can compile and run the program with these commands:

javac AsciiArt.java java AsciiArt

and if correct, you should see this output:

XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX

Lab Assignment - Part 2: write the printTriangle() method

Edit the AsciiArt.java program that is provided for this lab
(You don't need to do this if the program AsciiArt.java is still open in the gedit window):

Complete the printTriangle() method:

/* ================================================================ TODO: write this method printTriangle(h, c): Prints out a triangle with heigh equals to h using char c Example: printTriangle(3, 'A'): A AAA AAAAA *** NOTE: This method uses the "indentCharLine" method inside. ================================================================ */ public static void printTriangle(int h, char c) { .... }

(Hint: how many lines does it print ? How many characters does it print on line i ? How many spaces does it indent on line i ?

Write a for-loop using the answer of the above questions.)

After completing the printTriangle() method, you can compile and run the program with these commands:

javac AsciiArt.java java AsciiArt

and if correct, you should see this output:

A AAA AAAAA AAAAAAA AAAAAAAAA AAAAAAAAAAA AAAAAAAAAAAAA XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXX

Turn in
- You must turn in your work by enter these terminal commands:
  before midnight today.
For the Lead TA: