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Java Syntax

COMP122 Lectures

Java can be thought of as a sequence of statements with each statement ending with a semi-colon.

Comments

Everything after a double slash // is a comment.

Multi-line comments start with:

/*
and end in
*/

Blocks

Statements surrounded by curly brackets form a block. Blocks can be nested.

Example

/*
Author: Ben
The HelloWorld class implements an application that prints out "Hello World".
*/
public class HelloWorld {

	// Main Method
	public static void main(String[] args) {
		System.out.println("Hello World");
	}
}

The large block is a class definition which is named HelloWorld.

The main block is an actionable member of that class.

The class name must be the same as the name of the source code file in which it is defined (but with the extension .java

Java Keywords

There are some words that are reserved for the compiler can cannot be used for tother purposes such as variable names.

Main Methods

HelloWorld has only one method called main.

  • A class with a main method like this is called the application class.
  • The main method is the entry point of the application, from which the JVM begins the execution of the program.

Capitalisation and Indentation

  • Java is case sensitive so main is different to Main.
  • Indentation carries no meaning. The lines are ended by ;.

Code Conventions

  • Identifiers use CamelCase. Class names start in capitals; method and variable names in small letters.
  • Indent your code when nesting.
  • Add comments to explain what your code does.