Java Programming Introduction

Java Programming Introduction

• Java is a case-sensitive language.
• The main method is the entry point of a Java program.
• A program's output is displayed in the console window.
• A class in Java contains data items and methods.
• A package groups related classes.
• Each statement in a Java program ends with a semicolon (;).
• Code blocks are enclosed in curly braces { }.
• System.out.println() prints output to the console, followed by a new line.
• System.out.println("text"); prints the string "text"
• System.out.println(); prints a blank line.

Structure of a Java Program

• An executable Java program is a class.
• The class includes a method named main.
• The main method contains the statements (commands) to be executed.
• A method is a named group of statements.
• A statement is a command to be executed.

Programming Errors

• Syntax Errors: Detected by the compiler
• Runtime Errors: Cause the program to abort. Example: Division by zero
• Logic Errors: Produces incorrect results.

Identifiers

• Identifiers are names given to items in your program.
• Must start with a letter, underscore (_), or dollar sign ($).
• Cannot contain spaces or special characters.
• Cannot be reserved words (e.g., void, class, int).
• Cannot start with a number.

Strings

• A string is a sequence of characters to be printed.
• Strings start and end with double quotes (" ").
• The quotes themselves do not appear in the output.
• Strings cannot span multiple lines or contain double quote characters (").

Escape Sequences

• Escape sequences represent special characters within strings. Examples:
  • \t: Tab character
  • \n: Newline character
  • \": Double quote character
  • \\: Backslash character.

Comments

• Comments are notes within code that explain or clarify.
• Comments are ignored by the compiler.
• Single-line comments start with //.
• Multi-line comments start with /* and end with */.
• Comments are useful for complex programs and collaboration among programmers.

Compile/Run a Program

• Write: Create the source code (set of instructions).
• Compile: javac translates the source code into bytecode (which runs on the JVM).
• Run: java executes the bytecode to produce the output.

print vs. println

• System.out.println() adds a new line after printing.
• System.out.print() does not add a new line.