Introduction to Java Programming: A Brief History and Sample Program

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

2. 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).

3. A Java Application import java.util.Scanner; public class FirstProgram { public static void main(String[] args) { 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); } } >javac FirstProgram.java >java FirstProgram Enter an integer: 15 Enter another integer: 7 The sum is: 22 >

4. 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!

5. … 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.

6. … 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.

7. 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.

8. … 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();

9. … 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!

10. Compiling and Runninga 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>

11. 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!

12. 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.