CS-151 Labs > Lab 1. The First Cup of Java

Part 1. Pyramids revisited

Add a new Java class to your project. This time, use lab1 as the package name. Use Pyramid as the name of the class and check the button for including a public static void main stub.

For your first more serious program, we want you to create a class called Pyramid that draws a simple 2D pyramid out of * characters. Your program will:

• Check that the user has entered exactly 1 command-line argument. To do this, use the String array parameter to main called args, and check that args.length is equal to 1. If it isn’t, you should print a message to the user and then quit by calling System.exit(1);

• Convert the command line argument to an integer. Integer.parseInt() is a static method in the Integer class that allows you to convert a String that represents a number and turn it into an int. Convert the first argument args[0] into an int that represents the number of rows in your pyramid.

  int height = Integer.parseInt(args[0]);
  

• Print out the pyramid

Here are some examples of inputs and outputs. (Recall from the Lab 0 that the way you provide command line arguments in Eclipse is from the Run As > Run Configurations… menu option and then click on the Arguments tab.)

input: 5
output:
    *
   ***
  *****
 *******
*********

input: 1
output:
*

No input
output: 
To run: java Pyramid <number>

You may want to spend a couple of minutes figuring out how many stars and how many spaces you would need to print on each line as a function of height and loop iteration variable.