1. Introduction to Java Utilities

1.1 What are Utility Classes

Utility classes provide reusable methods for common tasks.

1.2 Importance

Reduces code complexity
Saves development time
Improves performance

2. String Class

2.1 What is String

A String is a sequence of characters.

2.2 Immutability

Strings cannot be changed once created.

2.3 Creating Strings

String s1 = "Hello";
String s2 = new String("World");

2.4 Common Methods

s1.length();
s1.charAt(0);
s1.substring(1);
s1.equals(s2);

2.5 Comparison

== → compares reference
equals() → compares value

3. StringBuilder and StringBuffer

3.1 Definition

Used for mutable strings (can be modified).

3.2 Example

StringBuilder sb = new StringBuilder("Hello");
sb.append(" World");
System.out.println(sb);

3.3 StringBuilder vs StringBuffer

Feature	StringBuilder	StringBuffer
Thread-safe	No	Yes
Performance	Faster	Slower

3.4 Common Methods

append()
insert()
delete()
reverse()

4. Date and Time API

4.1 Introduction

Java provides java.time package for date and time.

4.2 Example

import java.time.LocalDate;LocalDate today = LocalDate.now();
System.out.println(today);

4.3 LocalDateTime

import java.time.LocalDateTime;LocalDateTime now = LocalDateTime.now();

4.4 Formatting

import java.time.format.DateTimeFormatter;DateTimeFormatter dtf = DateTimeFormatter.ofPattern("dd-MM-yyyy");
System.out.println(today.format(dtf));

5. Math Class

5.1 Definition

Provides methods for mathematical operations.

5.2 Common Methods

Math.abs(-10);
Math.sqrt(25);
Math.pow(2, 3);
Math.max(10, 20);

5.3 Random Numbers

Math.random();

5.4 Rounding

Math.ceil(4.2);
Math.floor(4.8);
Math.round(4.5);

Conclusion

Java utility classes make programming easier and more efficient. By understanding how to work with strings, dates, and mathematical operations, beginners can write cleaner and more optimized code. These utilities are widely used in real-world applications and are essential for every Java developer.

Basic Java Utilities