Learn Java Programming

int a = 10, b = 3;
System.out.println(a + b);   // 13 (addition)
System.out.println(a - b);   // 7  (subtraction)
System.out.println(a * b);   // 30 (multiplication)
System.out.println(a / b);   // 3  (integer division — truncates!)
System.out.println(a % b);   // 1  (modulus — remainder)

// To get decimal result, cast one operand to double
System.out.println((double) a / b);  // 3.3333...

// Increment and decrement
int x = 5;
x++;        // x is now 6 (post-increment)
++x;        // x is now 7 (pre-increment)
x--;        // x is now 6 (post-decrement)

// Math class for advanced operations
System.out.println(Math.pow(2, 10));   // 1024.0
System.out.println(Math.sqrt(144));     // 12.0
System.out.println(Math.abs(-42));      // 42

int x = 10, y = 20;
System.out.println(x == y);   // false (equal to)
System.out.println(x != y);   // true  (not equal to)
System.out.println(x > y);    // false (greater than)
System.out.println(x < y);    // true  (less than)
System.out.println(x >= 10);  // true  (greater than or equal)
System.out.println(x <= 10);  // true  (less than or equal)

// IMPORTANT: == for objects compares REFERENCES, not values!
String s1 = new String("hello");
String s2 = new String("hello");
System.out.println(s1 == s2);       // false (different objects)
System.out.println(s1.equals(s2));  // true  (same content)

// String pool: literals share the same reference
String a1 = "hello";
String a2 = "hello";
System.out.println(a1 == a2);       // true (same pool object)

boolean isAdult = true;
boolean hasLicense = false;

// AND — both must be true
System.out.println(isAdult && hasLicense);  // false

// OR — at least one must be true
System.out.println(isAdult || hasLicense);  // true

// NOT — inverts the boolean
System.out.println(!isAdult);  // false

// Short-circuit evaluation: right side NOT evaluated if left determines result
String name = null;
if (name != null && name.length() > 0) {
    // Safe! If name is null, length() is never called
    System.out.println(name);
}

// Practical: validate before access
int[] arr = null;
boolean hasData = arr != null && arr.length > 0;

int x = 10;
x += 5;    // x = x + 5 = 15
x -= 3;    // x = 15 - 3 = 12
x *= 2;    // x = 12 * 2 = 24
x /= 4;    // x = 24 / 4 = 6
x %= 4;    // x = 6 % 4 = 2

// String concatenation with +=
String msg = "Hello";
msg += " World";  // "Hello World"

// Compound assignment also works with bitwise
int flags = 0b1100;
flags |= 0b0011;  // 0b1111 (set bits)
flags &= 0b1010;  // 0b1010 (clear bits)

int age = 20;

// condition ? valueIfTrue : valueIfFalse
String status = (age >= 18) ? "Adult" : "Minor";
System.out.println(status);  // Adult

// Practical: safe null handling
String name = null;
String display = (name != null) ? name : "Guest";
// Or in Java 9+: Objects.requireNonNullElse(name, "Guest")

// Nested ternary (avoid — prefer if/else for readability)
String grade = (age >= 65) ? "Senior" : (age >= 18) ? "Adult" : "Minor";

Object obj = "Hello, World!";

// Traditional instanceof
if (obj instanceof String) {
    String s = (String) obj;  // manual cast
    System.out.println(s.length());
}

// Pattern matching instanceof (Java 16+) — cast built in!
if (obj instanceof String s) {
    System.out.println(s.length());  // s already cast, no explicit cast needed
}