Classes  All code in a Java program is part of a class  A class has two purposes  Provide functions to do work for the programmer  Represent data  Two kinds of things found in a class  Variables store data about the class  Methods provide programmers with ways of asking the class to do work

Files in a Java program  A Java program is always made up of one or more classes  Most files in a Java program have a single class  A Java program will have many different files, typically one for each class.  The code is stored in a file with the same name as the class and the extension.java.  The java compiler creates a file with the same name, but the extension.class.

Defining a Class class myClass {... } 1. Starts with the word “class” 2. Followed by the class name 3. Followed by an open curly bracket 4. Followed by method and variable definitions. 5. Followed by a close curly bracket

Methods  A method is a piece of java code that does a job  Defined within the curly braces of a class definition  Two types  1. Static methods (also called class methods) do a job for a programmer  2. Instance methods manipulate the data within a class  For now we will talk about static methods

The parts of a method 1. Visibility Public - any part of the Java program can use it Private - can only be used within the same class 2. Type of method (static?) 3. Return type (what type of information it returns) 4. Name 5. Parameters - Data given to the method to do its job. 6. Body - The statements that get executed when the method is called.

Parts of a Method public static void main (String[ ] args) { System.out.print(“Hey there!”); } 1. Visibility 2. Static 3. Return type (void means nothing returned) 4. Method name 5. List of parameters 6. Body inside curly brackets

Indenting Classes  Variables and methods in a class should be indented  Close bracket at end should be indented the same as class  Open bracket can be on same line as class or next line  Classes are usually in their own file class myClass {//start of myClass void method1() {//start of method1 code; }//end method1 }// end myClass

Indenting Methods and Functions  Statements inside the method or function must be indented  Close bracket at end should be indented the same as the definition  Open bracket can be on same line or next line void myMethod() { statement1; }

Running a Java method  The body of a method between the curly brackets contain one or more statements  Statements are separated from one another by semicolons  When a method is called, it executes the statements one at a time  When Java is run, it looks for a method called main and runs it  The main method can call other methods, either in the same class or in other classes.

Some common methods  System.out.println(“I pwn all noobs”);  System.out.println prints whatever is inside the parentheses to the console  Moves the console cursor to a new line when it is done.  System.out.print(“U just got served”);  Similar to System.out.println, but does not move the cursor to a new line.

Formatting Java Programs  Java is case sensitive. E.g. System.out.println is not the same as system.out.println.  Java is white space insensitive  Can put any number of spaces or new line characters between statements  Should use spaces to indent to make programs readable  // (two slashes) in Java start a comment: // This is a comment  Everything from the // to the end of line is ignored

Summary  Java programs are made up of classes  Classes have variables that store data  Methods do work for the programmer  Class and method definitions have multiple parts.  The body of a method contains one or more statements.  End with a semicolon  Are executed in order when the method is run  The main method is run when a Java program starts  System.out.print/println send output to the console  Comments and extra white space are ignored

Project 0  Work on Project 0  Due date : Tomorrow!