Java Reference

The Java Reference section provides a quick and structured overview of important Java concepts, syntax, keywords, classes, and commonly used methods. It is designed to help students revise topics quickly and find definitions or examples without reading long explanations.

This reference guide is especially useful for exam preparation, interviews, and last-minute revision.

1. Java Basic Syntax

Every Java program starts with a class and a main method.

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

2. Java Data Types

Java supports two types of data types:

Primitive Data Types – int, double, float, char, boolean, byte, short, long
Non-Primitive Data Types – String, Arrays, Classes, Interfaces

int age = 20;
double price = 99.99;
char grade = 'A';
boolean isPassed = true;

3. Java Operators

Arithmetic: +, -, *, /, %
Relational: ==, !=, >, <, >=, <=
Logical: &&, ||, !
Assignment: =, +=, -=, *=

4. Java Control Statements

Control statements are used to control the flow of execution.

if, if-else, switch
for loop, while loop, do-while loop
break, continue

for(int i = 1; i <= 5; i++){
System.out.println(i);
}

5. Java OOP Concepts

Class – Blueprint of an object
Object – Instance of a class
Inheritance – Acquiring properties of another class
Polymorphism – Many forms of a method
Encapsulation – Wrapping data and methods together
Abstraction – Hiding implementation details

class Person {
  String name;
  void display() {
    System.out.println(name);
  }
}

6. Java Arrays

Arrays are used to store multiple values of the same data type.

int[] numbers = {1, 2, 3, 4};
System.out.println(numbers[0]);

7. Java Strings

The String class is used to handle text in Java.

String text = "Java";
System.out.println(text.length());
System.out.println(text.toUpperCase());

8. Java Exception Handling

Exception handling prevents runtime errors from crashing the program.

try {
int result = 10 / 0;
} catch (ArithmeticException e) {
System.out.println("Error occurred");
}

9. Java Collections

The Java Collections Framework provides classes like ArrayList, HashSet, and HashMap to store and manipulate groups of objects.

import java.util.ArrayList;

ArrayList<String> list = new ArrayList<>();
list.add("Java");
list.add("Python");
System.out.println(list);

10. Java Keywords (Commonly Used)

public
private
protected
static
final
class
interface
extends
implements
return

Why Java Reference is Important?

Quick revision before exams
Helpful for coding practice
Useful during interviews
Provides structured overview of Java
Saves time while revising concepts

Helpful Tip: Keep practicing examples from each section. Java Reference is best used along with hands-on coding practice.