MANOJ K

Posted on Aug 26

Introduction to Java - Basics

Java is one of the most popular and widely used programming languages in the world. It is simple, secure, and platform-independent, making it a favorite among beginners and professionals alike. If you’re starting your journey with Java, here are some core concepts you should understand.

1.. Keywords

*Keywords are reserved words in Java that have a special meaning.
*Examples: class, int, if, else, for, public, static.
*You cannot use keywords as variable names, method names, or identifiers.
*Java has 50+ keywords.

2.. Tokens

*A token is the smallest unit of a Java program.
Types of tokens:
1)Keywords
2)Identifiers
3)Literals
4)Operators
5)Separators (; , { } [ ])

3.. Identifiers

*Identifiers are names given to variables, methods, classes, or objects.
*Examples: age, Student, main, calculateSum.

*Rules for Identifiers:

1) Can contain letters, digits, _, and $.
2) Cannot start with a digit.
3) Cannot use keywords.
4) Case-sensitive (Age ≠ age).
5) No spaces allowed.

4.. Literals

Literals are fixed values written directly in the code.
Types of Literals:

1) Integer → 10
2) Floating-point → 3.14
3) Character → 'A'
4) String → "Hello"
5) Boolean → true, false
6) Null Literal → null

5.. Declaration & Initialization

Declaration: Telling the compiler about a variable.
```
    int age;
```

*Initialization: Assigning a value to a variable.

        age = 20;

Both together:
```
    int age = 20;
```

6.. Features of Java

Simple & Object-Oriented
Platform Independent (WORA – Write Once, Run Anywhere)
Secure
Robust (strong memory management)
Portable
Multithreaded
High Performance (with JIT Compiler)

7.. History of Java

Developed by James Gosling at Sun Microsystems in 1991.
Released to the public on 23 May 1995.
Originally called Oak, later renamed Java.
Currently owned by Oracle Corporation.

8.. Operators

*Operators are symbols that perform operations.

*Types of Operators:

1) Arithmetic → + - * / %
2) Relational → < > <= >= == !=
3) Logical → && || !
4) Assignment → = += -=
5) Unary → ++ --
6) Ternary → ?:

9.. Data Types

*Java data types define the kind of data a variable can hold.

1) Primitive Types (8):

*byte, short, int, long (integers)
*float, double (decimals)
*char (characters)
*boolean (true/false)

2) Non-Primitive Types:

*String, Arrays, Classes, Objects

10.. Class and Object

Class: A blueprint for objects.

class Student {
String name;
int age;
}

Object: An instance of a class.

Student s1 = new Student();

11.. Methods and Types

A method is a block of code that performs some task.
Types of methods:

1) Predefined Methods – already available in Java (e.g., System.out.println())

2) User-defined Methods – created by programmers.

12.. Number System Conversions

Java supports different number systems:
Decimal ↔ Binary ↔ Octal ↔ Hexadecimal
Examples:

1) Decimal (10) → Binary (1010)

2) Decimal (10) → Octal (12)

3) Decimal (10) → Hex (A)

13.. Program Execution Life Cycle

Steps in executing a Java program:

1) Write Code → Create .java file.
2) Compile → javac generates .class bytecode.
3) Class Loader → Loads bytecode into JVM.
4) Bytecode Verifier → Checks security and errors.
5) Interpreter / JIT Compiler → Converts bytecode to machine code.
6) Execution → Runs on CPU.