Object-Oriented Programming in Java

Primitive Data Types

Java has eight primitive data types used for basic storage needs. They differ in size, range, and typical usage.

• byte – 1 byte, integer range -128 to 127
• short – 2 bytes, small integer values
• int – 4 bytes, default integer type
• long – 8 bytes, larger numeric values
• float – 4 bytes, decimal numbers (single precision)
• double – 8 bytes, decimal numbers (double precision)
• char – 2 bytes, Unicode character
• boolean – true or false

int age = 19;
double gpa = 8.6;
char grade = 'A';
boolean isValid = true;

Diagram to add: java-primitive-sizes.png

Variables, Type Conversion and Casting

Java automatically performs widening conversions (small to large type), while narrowing conversions require explicit casting.

• Widening: int to long, float to double (automatic)
• Narrowing: double to int, long to short (explicit cast)

int a = 10;
double b = a;        // widening

double x = 9.76;
int y = (int) x;     // narrowing, y = 9

Arrays

Arrays store multiple values of the same type. They are objects and have fixed length determined at creation.

int[] marks = {85, 90, 75};
for (int i = 0; i < marks.length; i++) {
  System.out.println(marks[i]);
}

Diagram to add: java-array-memory.png

Strings

Strings are immutable objects. Java stores them in a special "String pool" for memory optimization.

String s = "openCSE";
System.out.println(s.length());
System.out.println(s.toUpperCase());

Operators and Precedence

Java provides arithmetic, relational, logical, bitwise and assignment operators. Parentheses improve readability and override precedence.

int a = 2 + 3 * 4;     // 14
int b = (2 + 3) * 4;   // 20

boolean result = (a < b) && (b < 50);

Diagram: operator-precedence-java.png

Control Statements

Control statements determine program flow. Java provides selection, iteration, and jump statements.

• Selection: if, if-else, switch
• Iteration: for, while, do-while, enhanced for
• Jump: break, continue

int n = 7;

// if-else
if (n > 0) System.out.println("positive");

// switch
switch (n) {
  case 1: System.out.println("one"); break;
  default: System.out.println("other");
}

// loop
for (int i = 0; i < 5; i++) {
  if (i == 3) continue;
  System.out.println(i);
}

Diagram: loop-flowcharts.png