Learn Java Programming

int score = 82;

if (score >= 90) {
    System.out.println("Grade: A");
} else if (score >= 80) {
    System.out.println("Grade: B");
} else if (score >= 70) {
    System.out.println("Grade: C");
} else if (score >= 60) {
    System.out.println("Grade: D");
} else {
    System.out.println("Grade: F");
}
// Output: Grade: B

// Combining conditions with logical operators
int age = 25;
boolean hasID = true;
if (age >= 18 && hasID) {
    System.out.println("Access granted");
} else {
    System.out.println("Access denied");
}

// Null-safe checking (check null FIRST)
String name = null;
if (name != null && name.length() > 0) {
    System.out.println("Hello, " + name);
} else {
    System.out.println("Hello, Guest");
}

int dayNum = 3;
String dayName;

switch (dayNum) {
    case 1:
        dayName = "Monday";
        break;  // Without break, execution falls through!
    case 2:
        dayName = "Tuesday";
        break;
    case 3:
        dayName = "Wednesday";
        break;
    case 6:
    case 7:
        dayName = "Weekend";  // Multiple cases sharing one block
        break;
    default:
        dayName = "Unknown";
}
System.out.println(dayName);  // Wednesday

// switch works with: int, char, String (Java 7+), enums
String command = "START";
switch (command) {
    case "START": startServer(); break;
    case "STOP":  stopServer(); break;
    default: System.out.println("Unknown command");
}

int day = 3;

// Arrow syntax — no break needed, no fall-through
String name = switch (day) {
    case 1 -> "Monday";
    case 2 -> "Tuesday";
    case 3 -> "Wednesday";
    case 4 -> "Thursday";
    case 5 -> "Friday";
    case 6, 7 -> "Weekend";  // Multiple labels
    default -> "Invalid";
};
System.out.println(name);  // Wednesday

// Switch with blocks and yield
String category = switch (day) {
    case 1, 2, 3, 4, 5 -> {
        System.out.println("Processing weekday...");
        yield "Weekday";  // yield returns a value from a block
    }
    case 6, 7 -> {
        yield "Weekend";
    }
    default -> throw new IllegalArgumentException("Invalid day: " + day);
};

int age = 20;

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

// Practical: null-safe default
String input = null;
String value = (input != null) ? input : "default";

// Nested ternary (avoid for readability)
String category = (age < 13) ? "Child" : (age < 18) ? "Teen" : "Adult";