Java Basics

Commenting

// Single line comment

/*
Multiple
Lines
Comment
*/

/** JavaDoc Comment */

JavaDoc should be avoided due to keep the code clean

Naming Convention

• Class name identifier should start with capital letter e.g. public class Welcome1
• Identifier can comprise of letter, number, underscore, and $. But $ should be avoided as it is usually used by compiler for special things.
• For multi-word class name, use PascalCase.

Java is case-sensitive language

Entry Point

• public static void main(String[] args)
• main method must be all lower case letters

Library

• All classes under java.lang e.g. System, String are automatically imported.

Command Line

Compilation

> javac Welcome1.java

• .class file (Java byte code) is generated and can be JIT-compiled and execued by JVM

Execution

> java Welcome1
Welcome to Java Programming!

Online Documentation

• https://docs.oracle.com/javase/8/docs/ --> Java SE API

Primitive Types vs. Reference Types

8 Primitive Types

• • boolean
  • byte - 1-byte integer
  • char - 1-byte unsigned integer
  • short - 2-byte integer
  • int - 4-byte (32 bit) integer
  • long - 8-byte (64 bit) integer
  • float - 4-byte decimal number
  • double - 8-byte decimal number
• All types are initialized with 0 except boolean that is initialized as false.
• Java guarantees fixed size of each primitive types, not varying by system
• boolean is not a number in Java

Reference Types

• All non-primitive types, usually start with Capital leter
• Is an object so initialized as null
• Can contain instance variables and methods