1. Lecture Note Set 1 Thursday 12-May-05
CIS3931 – Intro to JAVA
Lecture Note Set 1
Thursday 12-May-05

2. A basic JAVA program // Class declaration public class Welcome1 {
public static void main( String args[] )
System.out.println(“Welcome to Java”);
} //end of main method
} //end of class

3. Compiling a JAVA program
Command = javac <filename.java>
Compiler will potentially return with error messages
Error messages = time to debug your code
Debugging = Correcting syntax errors in your code
No errors = runtime testing

4. Running a JAVA program java <filename>
Example to run the class file “example.java” you would type java example
Runtime testing = Making sure your program performs as expected

5. Variables A place to store values in memory Many different types
int = integer – A whole number value (ex : 12)
char = character – A single character (ex: c)
String = characters (ex: hello)
float = floating point number (ex : 3.14)

6. Variable examples (declarations)
int a = 1; //assigns the value 1 to a
int b = //assigns the result of to b
int c = a + b //assigns the result of a + b to c
a+ = 1; //assigns the result of a + 1 to a
String cup = new String(“cup of Java”);
// assigns the literal “cup ofJava” to cup

7. Variable Casting It is possible to cast one variable type to another
Example : A character is actually just a special case of an integer …
The character “A” has the integer value 65

8. Text Formatting
Text is printed to the screen with either of the following commands
System.out.println(“Insert Text Here”);
System.out.print(“Insert Text Here”);
System.out.print(“hello\n”); is equivalent to
System.out.println(“hello”);

9. Text formatting
Column formatting can be accomplised with the /t escape character
Example :
System.out.println(“a\tb\tc\td”);

10. Comments There are two types of comments in JAVA Single line comments
//This is a single line comment
Block comments
/* This is a
block comment*/

11. The JAVA API http://java.sun.com/j2se/1.5.0/docs/api/
The most useful tool when programming in JAVA
Many algorithms and functions are already written for you

12. Using the API
You have to “import” the class that contains the functions you want to use
Example :
Import java.io.* will allow you to use anything in the java.io class

13. User Input Use BufferedReaders.
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String input = br.readLine();
int num1 = Integer.parseInt(input);
BufferedReader is in java.io.*