Introduction to Java Brief history of Java Sample Java Program - PowerPoint PPT Presentation

Introduction to Java  Brief history of Java  Sample Java Program  Compiling & Executing Reading: => Section 1.1 1

Introduction to Java History  Invented in 1991 - Sun Microsystems, Inc (James Gosling).  Sun Microsystems was purchased by Oracle Corporation in 2010.  Originally a language for programming home appliances.  Later (1994) used for internet applications and general-purpose programming. Why the name “Java”?   Supposedly came from a list of random words (wikipedia). 2

A Java Application >javac FirstProgram.java import java.util.Scanner; >java FirstProgram Enter an integer: public class FirstProgram 15 { Enter another integer: public static void main(String[] args) 7 { The sum is: 22 int n1, n2; > Scanner keyboard = new Scanner(System.in); System.out.println(“Enter an integer:”); n1 = keyboard.nextInt(); System.out.println(“Enter another integer:”); n2 = keyboard.nextInt(); System.out.println(“The sum is:”); System.out.println(n1 + n2); } } 3

Explanation of Code ...  Code at the beginning of the program (to be explained later): import java.util.Scanner; public class FirstProgram { public static void main(String[] args) {  Java applications all have similar code at the beginning  The name of the class differs from one program to another.  The name of the class is also the name of the file.  Notice that the blank line is gone! 4

… Explanation of Code ...  The following creates two variables named n1, n2 for storing two whole numbers (integer): int n1, n2; These are called “variable declarations.”  In this program they are used to store the user’s response.  5

… Explanation of Code ...  The following creates an object called keyboard of the Scanner class: Scanner keyboard = new Scanner(System.in); System.in refers to the keyboard   The Scanner class provides the program with access to keyboard input. 6

Explanation of Code ... Displays a “text” string to the screen:  System.out.println(“Enter an integer:”); Note the “dot” delimiter:   System is a class  out an object  println is a method that outputs something  Double-quoted text inside the parentheses is referred to as an argument or parameter to the method. 7

… Explanation of Code ... The following inputs (or “reads”) an integer typed in using the keyboard and  stores it in the variable n1 : n1 = keyboard.nextInt();  The next two lines are similar: System.out.println (“Enter another integer:”); n2 = keyboard.nextInt(); 8

… Explanation of Code  The following prints the sum to the console (or screen): System.out.println(“The sum is:”); System.out.println(n1 + n2); By the way, every character counts! 9

Compiling and Running a Java Program  Type the program into a file:  FirstProgram.java Make sure you get the file name correct!  Compile (from the command-line, i.e., DOS):  javac <file>.java  Run (and link):  java <file> 10

Extra Work – Yippee!  Type-in, compile and run the previous program. Experiment with “what if” scenarios:   Add some syntax errors  Run the program incorrectly – input improper data  Modify the program to work with 3 ints  Note that if you change the program, you have to recompile before you rerun! 11

Some Helpful Commands  Some helpful commands:  cd <dir-name> - change directory  cd .. - move up a directory  dir <pattern> - list directory contents matching the pattern  mkdir <dir-name> - create a new directory  del <pattern> - delete a file or files matching the pattern Suggestion – create a new directory/subfolder on your “C” drive to store  all class related programs.  Create subfolders as appropriate. 12