Lesson 42: Essential Utility Classes

Java provides many utility classes, often containing static methods, that simplify common tasks.

1. The Math Class

Contains methods for performing basic numeric operations, such as elementary exponential, logarithm, square root, and trigonometric functions.

• All methods and fields are static.
• Fields: Math.PI, Math.E.

java // Square root double root = Math.sqrt(81.0); // 9.0

// Rounding long rounded = Math.round(3.7); // 4

// Max/Min int maxVal = Math.max(10, 20); // 20

// Power double power = Math.pow(2, 3); // 8.0

2. The Random Class

Used to generate pseudo-random numbers.

java import java.util.Random;

Random random = new Random();

// Generate a random integer int randInt = random.nextInt();

// Generate a random integer between 0 (inclusive) and 100 (exclusive) int diceRoll = random.nextInt(100);

// Generate a random double between 0.0 (inclusive) and 1.0 (exclusive) double randDouble = random.nextDouble();

3. The Modern Date/Time API (java.time)

Introduced in Java 8, this API fixes many flaws of the old Date and Calendar classes. It is much clearer, immutable, and thread-safe.

• LocalDate: Date without time/timezone.
• LocalTime: Time without date/timezone.
• LocalDateTime: Date and time without timezone.

java import java.time.LocalDate; import java.time.LocalDateTime;

// Current date and time LocalDate today = LocalDate.now(); System.out.println(today);

// Specific date LocalDate birthday = LocalDate.of(1990, 10, 20);

// Manipulation (all these return new immutable objects) LocalDate nextWeek = today.plusWeeks(1);