Transcript 12-May-05 Power Point Presentation

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.*