Int Programming--Malone

Basics of Java Programming
(A Work In Progress) What Constitutes a Java Program? A Java program consists of one or more source files. Each source file is called .java, where is the name of the class contained in that source file and .java is the extension that identifies the file as a Java source code file. In general, each source file contains one class. The name of the class must match the name of the file (without the extension) exactly. To execute a Java program, you first need to compile the source code into byte code. Byte code files have the name .class. If you’re working from the shell, this is done using the javac command (where “c” is for compiler). Usually we will be compiling using the Xcode IDE. Once compiled, the program is executed using the Java interpreter (a.k.a. the Java Virtual Machine or JVM). From the shell, the JVM is invoked with the “java” command. Again we will usually be doing this with the Build and Go or Debug options of the Xcode IDE. A Java program must have a routine called main(), which is the starting point for program execution. main() will always look something like this: public static void main (String args[]) { // insert code here... System.out.println("Hello World!"); } Source Code Formatting Keep in mind the following when writing Java source code: Java is case sensitive (“foo”, “Foo”, and “fOO” are all considered to be different in Java). • Every line of code in Java must end in a semi-colon (“;”). • Java doesn’t care about white space (line breaks, tabs, etc.) but consistent and thoughtful use of white space makes code much easier to read and is part of good programming style. • You can create comments in Java using // for a single-line comment or /* */ for a block comment. Examples: // This comment is just this one line /* This comment includes many lines. Code inside is inactive (“commented