1. Anatomy of a Class LIS4930 © PIC The name of the method The name of this class This is a class The return type. Void means there is nothing returned Opening of curly brace of the class Arguments to the method. This method must be given an array of String, and the array will be called ‘args’ Public so everyone can access it public class MyFirstApp { public static void main (String [ ] args ) { System.out.println (“I Rule!”) ; } } Opening brace of the method We’ll cover this later. Every statement MUST end in a semicolon! Closing brace of the MyFirstApp class A string you want to print This says print to standard output (defaults to command-line) Closing brace of the method DONT WORRY ABOUT MEMORIZING ANYTHING RIGHT NOW… THIS IS JUST SOMETHING TO GET THAT SWEET JAVA AMORA IN THE AIR

2. The main thing is to keep the main thing the main thing. ~ Stephen Covey When the JVM (Java Virtual Machine) starts running, it looks for the class you give it at the command line. Then it starts looking for a specifically-written method that looks exactly like: public static void main (String [ ] args) { //your code goes here } What’s this? This is called the “main” method, and the JVM runs everything between the curly braces { } of this main method. Every Java application has to have as least one class, and at least one main method. (NOT one main per class; just one main per application).The main( ) method tells the computer where to start, and you only need one starting place. LIS4930 © PIC

3. Writing a Class with a Main LIS4930 © PIC In Java everything goes into a class. You’ll type your source code file (with a .java extension), then compile it into a new class file (with a .class extension). When you run your program, you’re really running a class. 1 MyFirstApp.java public class MyFirstApp { public static void main (String [ ] args) { System.out.println(“I Rule!”); System.out.println(“The World”); } } Save 2 Compile javac MyFirstApp.java 3 java MyFirstApp Run

4. What can the main method do? LIS4930 © PIC Your code can tell the JVM to: do something again and again do something under this condition do something while (x >12) { x = x + 1; } for (intx = 0; x < 10; x = x + 1) { System.out.print(“x is now “+ x); } if (x == 10) { System.out.print(“x must be 10”); } else { System.out.print(“x isn’t 10”); } if ((x < 3) & (name.equals(“Kyle”))) { System.out.println(“Gently”); } System.out.print(“This line runs no matter what”); intx = 3; String name = “Kyle”; x = x +17; System.out.print(“x is “ + x); double d = Math.random(); //this is a comment 1 2 3 Statements: declarations, assignments, method calls, etc. Loops: for and while Branching: if…else tests

5. Syntax Fun Each statement must end in a semicolon: x = x + 1; A single-line comment begins with two forward slashes: x = 22; //this is a comment Most white space doesn’t matter: x = 3 ; Variables are declared with a name and a type(you’ll learn about all the Java types in chapter 3). intweight; //type: int, name: weight Classes and methods must be defined within a pair of curly braces. public void go( ) { //amazing code here } LIS4930 © PIC

6. Looping, Looping, Looping LIS4930 © PIC Java offers three types of looping structures: while, do-while, and for. We’ll discuss the others later, but for now we will only discuss while. The while loop keeps looping as long as some condition is true, this is called the conditional test. What is done on each loop is found inside the loop block, which is located after the conditional test within The key to a loop is a conditional test. In Java, a conditional test is an expression that results in a boolean value – in other words, something that is either true or false. curly braces. while (moreBalls == true) { keepJuggling( ); }

7. Simple Boolean Tests LIS4930 © PIC You can do a simple boolean test by checking the value of a variable, using a comparison operator including: < (less than) > (greater than) == (equality) intx = 4; //assign 4 to x while (x > 3) { // loop code will run because // xis greater than 3 x = x – 1; } intz = 27; while (z == 17) { // loop code will not run because // z is not equal to 17 } Yes that is TWO equal signs. Notice the difference: the assignment operator is = and the equality operator is ==. Lots of programmers accidently type = when they want ==, but not you 

8. Example of a while loop LIS4930 © PIC public class Loopy { public static void main (String[ ] args) { intx = 1; System.out.println(“Before the Loop.”); while (x < 4) { System.out.println(“In the loop”); System.out.println(“Value of x is “ + x); x = x + 1; } System.out.println(“This is after the loop”); } } Let’s see how it works

9. Conditional Branching LIS4930 © PIC public class IfTest { public static void main (String[ ] args) { intx = 3; if (x == 3) { System.out.print(“x must be 3”); } System.out.print(“This runs no matter what”); } } public class IfTest { public static void main (String[ ] args) { intx = 3; if (x == 3) { System.out.println(“x must be 3”); } System.out.println(“This runs no matter what”); } } What’s different?

10. Conditional Branching LIS4930 © PIC public class IfTest { public static void main (String[ ] args) { intx = 3; if (x == 3) { System.out.println(“x must be 3”); } else { System.out.println(“x is NOT 3”); } System.out.println(“This runs no matter what”); } } What about this one? What is this?

11. Coding a Serious Business Application LIS4930 © PIC With the tools we have covered up to this point you have just about enough skills to code your first program. Who knows the lyrics to “99 Bottles of Beer on the Wall”? So how do we do it, what do we need?

12. Be Prepared ~ Robert Baden-Powell Before you start programming begin with creating prepcode. Use keywords like: LIS4930 © PIC A form or pseudocode, to help you focus on the logic without stressing about syntax.

13. What would the prepcode look like for “99 bottles of beer on the wall”? LIS4930 © PIC Prepcode for “99 bottles of beer on the wall”. DECLARE counter SET to 99 REPEAT until counter EQUALS 1 PRINT counter + “bottles of beer on the wall,” PRINT counter + “bottles of beer.” PRINT “Take one down and pass it around,” DECREMENT counter IF counter EQUALS 1 PRINT counter + “bottle of beer on the wall.” END IF ELSE PRINT counter + “bottles of beer on the wall.” END ELSE END REPEAT PRINT counter + “bottle of beer on the wall,” PRINT counter + “bottle of beer.” PRINT “Take one down and pass it around,” PRINT “no more bottles of beer on the wall.”

14. Try it Yourselves! Work with the person sitting next to you (groups of two ONLY). Write prepcode, as demonstrated in class, for creating a Java program to print out the lyrics to a popular camp/bus song. Use a word processor to type up your final draft and save it for later. Raise your hand for the teacher or TA to inspect your group’s final draft and give suggestions on how it might be improved. Have the TA signoff the attendance sheet to mark you were present in class and did the work. LIS4930 © PIC

15. Homework! Practice writing prepcode. Install Eclipse. Experiment with writing your first Java program. Quizzes start next week… (I won’t remind you every again – quizzes are listed on the Course Content page) LIS4930 © PIC