Comp 110

Lab Project #1

8/24/2009

The purpose of this assignment is to learn how to create, compile and execute java programs in the environment provided. Don’t worry too much about the syntax of the Java code. The meaning of all the keywords used and the use of various delimiters and symbols will be explained over the next several class sessions. Just concentrate on the process you must follow to create java programs, to get them compiled, and to execute (run) them. For each of the problems below show the instructor the successful results you obtained before going on to the next problem. If you have any difficulty or have questions ask the instructor for help.

Problem 1: Create a simple application called “Hello, world!” that does nothing but print out the statement “Hello, world!” when executed. This is about the simplest java program we can create. Once the program is created, compile it. If you encounter errors in the compilation process, fix the errors and try to compile it again. Continue this process until it compiles correctly. Finally execute the program and check to see that it correctly prints the statement “Hello, world!”. To accomplish this follow the following steps:

1. Open the jGRASP application (double click on the jGRASP icon on the desktop)

2. Type the following text into the window provided:

public class Hello {

public static void main(String [] args) {

System.out.println("Hello, world!");

}

}

3. Save the file using the save command in the File menu.

4. Compile the source file by clicking the compile icon (the plus sign above the window where you typed your program). If you typed the program correctly, this step should complete with no error messages displayed in the output window at the bottom of the screen. If error messages are shown, you need to correct the errors in the file and then try to compile the program again. Repeat this process until the source file compiles correctly.

5. Execute the program created by clicking the run icon (the person running). You should see the message “Hello, world!” displayed in the window at the bottom.

Problem 2: Create a slightly more complex version of the program written above in which the user will interact with the program by typing in their name and receiving a customized greeting. Repeat the steps from Problem 1, except name this program CustomHello, and name the source file CustomHello.java. The file to be entered is as follows:

import java.io.*;

public class CustomHello {

public static void main(String [] args) throws Exception {

BufferedReader in = new BufferedReader(new

InputStreamReader(System.in));

String myname = null;

System.out.print("Please enter your name: ");

myname = in.readLine();

System.out.print("Hello, " + myname + "!");

}

}

Problem 3: This problem demonstrates how to input numerical information into a Java application. It asks the user to enter two integers, adds them together, and prints out the result. Repeat the steps used in the previous two problems except call this program Addition and name the source file Addition.java. This program is as follows:

import java.io.*;

public class Addition {

public static void main(String [] args) throws Exception {

BufferedReader in = new BufferedReader(new

InputStreamReader(System.in));

String s1 = null, s2 = null;

int n1, n2, sum;

System.out.print("Enter the first integer: ");

s1 = in.readLine();

n1 = Integer.parseInt(s1);

System.out.print("Enter the second integer: ");

s2 = in.readLine();

n2 = Integer.parseInt(s2);

sum = n1 + n2;

System.out.print("The sum of the values is " + sum);

}

}