Basics of Java language

Back to Java for DSA
Arjit Sharma
02 Mins

Now lets lay the groundwork for coding in java and that is knowing the essentials like variables, loops, and what not !

Variable and Constants

Variable- Name of reserved area allocated in memory.

int age = 18; // initializing a variable

Constants- A variable whose value cannot be changed once assigned.

final float PI = 3.14F;

Data Types in Java

  1. Primitive Types

    Java has 8 built-in primitives:

    • Integer types: byte(1), short(2), int(4), long(8)
    • Floating-point types: float(4), double(8)
    • Other: char(2), boolean(1)
byte age = 12;
char letter = 'Z';
boolean isDone = true;
float price = 99.99F;
long visitors = 9_891_232_321L;
  1. Reference Types

Any object instanced from a class is a reference variable. They store addresses in memory.

// java boilerplate
Person p1 = new Person("arjit",25);
Person p2 = p1; // p2 refers to the same object as p1

p2.name = "naruto"; // Changing p2 also updates p1 because both point to same memory
System.out.println(p1);

Inputs and Outputs in Java

// Ouput
System.out.println("Can be anything - "+ variableName); // Concatenation with + 
System.out.print();
System.out.printf("Formatted number: %.2f", 45.678);

// Input
import java.util.Scanner;
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();         // Reads an int
String word = sc.next();      // Reads one word
String line = sc.nextLine();  // Reads the whole line

You also get nextFloat(), nextDouble(), nextByte(), nextShort(), nextLong()
📌 Note - After calling nextInt() or similar, you might need to consume the leftover newline

Strings in Java

String is a sequence of characters.

String greeting = "Hello, World!";
System.out.println(greeting);  // Output: Hello, World!

String Immutability: Strings are immutable, meaning once created, their value cannot be changed.

String str = "Java";
str = str + " Programming";  // Creates a new string

Arrays in Java

Arrays store multiple values of the same type.

int[] numbers = {1, 2, 3, 4, 5};
String[] names = {"Arjit", "Raman", "Albert"};

System.out.println(names[0]);  // Output: Arjit

Type Casting

Changing a variable from one type to another.

  • Implicit Casting - Automatic widening conversion, that happens without specifying. byte > short > int > long > float > double
int x = 10;
double y = x; // int → double
  • Explicit Casting - Manual narrowing conversion, we need to specify.
// Example of explicity casting
double x = 4.5;
int res = (int)x + 1;

// Example of explicitly casting non-compatible types - string and numbers
// Also works for converting types like String → int:
String x = "1";
int res = Integer.parseInt(x) + 2;

Operators in Java

Operators let you perform calculations and comparisons.

// Comparison Operators
1==1, 1!=0, 2>=1, 2<=2, 5>3, 1<3

// Equality
==, !=

// Assignment
=, +=, -=, *=, /=, %=

// Logical Operators
&&, ||

// Unary Operators
var++, var-- // Postfix
++var, --var // Prefix

// Bitwise
&, |, ^, >> , <<, >>>

// Ternary Operator (?:)
int max = (a > b) ? a : b;
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