Variables & Data Types

1public class Variables {
2    public static void main(String[] args) {
3        // Primitive types
4        int age = 21;
5        double gpa = 3.85;
6        boolean isStudent = true;
7        char grade = 'A';
8 
9        // Reference type
10        String name = "Alice";
11 
12        // Constants
13        final double PI = 3.14159;
14 
15        System.out.println(name + " is " + age + " years old.");
16        System.out.println("GPA: " + gpa);
17    }
18}

1public class Casting {
2    public static void main(String[] args) {
3        // Widening (automatic)
4        int myInt = 42;
5        double myDouble = myInt; // int → double
6        System.out.println(myDouble); // 42.0
7 
8        // Narrowing (manual)
9        double pi = 3.14159;
10        int rounded = (int) pi; // double → int
11        System.out.println(rounded); // 3
12 
13        // String to int
14        String numStr = "100";
15        int num = Integer.parseInt(numStr);
16        System.out.println(num + 50); // 150
17    }
18}