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

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

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

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

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)

Variable examples (declarations) int a = 1; //assigns the value 1 to a int b = 1 + 1 //assigns the result of 1 + 1 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

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

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”);

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

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*/

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

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

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.*