LESSON 8

3.1 Lesson Outcomes

After completing this lesson, learners will be able to:

• Define strings in Java.
• Create and initialize string variables.
• Use common string methods.
• Concatenate and compare strings.
• Explain the importance of strings in Java applications.

3.2 Overview

Strings are one of the most commonly used data types in Java programming. Strings are used to store and process text such as names, messages, addresses, passwords, and user input.

This lesson introduces learners to Java strings and explains how strings are created and manipulated within Java applications. Learners will also explore commonly used string methods and operations used in real-world software systems.

Strings are widely used in:

• banking systems,
• websites,
• mobile applications,
• inventory systems,
• and enterprise software.

Understanding strings is essential because most software applications process textual data.

KT0801 — Introduction to Strings

A string is a sequence of characters stored as an object in Java.

Strings use the String class.

Example of a String

String name = "Java";

Explanation

Importance of Strings

Strings are used to:

• store text,
• display messages,
• process user input,
• and manage application data.

KT0802 — Creating Strings

Strings can be created using:

• string literals,
• or the new keyword.

String Literal Example

String language = "Java";

Using the new Keyword

String language = new String("Java");

Difference Between the Two Approaches

KT0803 — String Concatenation

Concatenation combines strings together.

Java uses the + operator for concatenation.

Example

public class Main {

    public static void main(String[] args) {

        String firstName = "Bukhosi";
        String lastName = "Moyo";

        String fullName = firstName + " " + lastName;

        System.out.println(fullName);
    }
}

Output

Bukhosi Moyo

Importance of Concatenation

Concatenation is used to:

• build messages,
• combine text,
• and generate application output.

KT0804 — Common String Methods

The String class provides built-in methods for processing text.

length() Method

Returns the number of characters in a string.

String word = "Java";

System.out.println(word.length());

Output

4

toUpperCase() Method

Converts text to uppercase.

String word = "java";

System.out.println(word.toUpperCase());

Output

JAVA

toLowerCase() Method

Converts text to lowercase.

String word = "JAVA";

System.out.println(word.toLowerCase());

Output

java

charAt() Method

Returns a character at a specified index.

String word = "Java";

System.out.println(word.charAt(0));

Output

J

KT0805 — Comparing Strings

Strings can be compared using the equals() method.

Example

public class Main {

    public static void main(String[] args) {

        String word1 = "Java";
        String word2 = "Java";

        System.out.println(word1.equals(word2));
    }
}

Output

true

Importance of equals()

The equals() method checks:

• user input,
• passwords,
• usernames,
• and application conditions.

KT0806 — String Immutability

Strings in Java are immutable.

This means:

• string values cannot be changed after creation.

When modifications occur:

• Java creates a new string object.

Example

String text = "Java";

text = text + " Programming";

System.out.println(text);

Output

Java Programming

Importance of Immutability

Immutability improves:

• security,
• performance,
• and memory management.

KT0807 — Real-World Use of Strings

Strings are used in:

• login systems,
• registration forms,
• banking systems,
• search engines,
• and communication systems.

Examples:

• customer names,
• email addresses,
• passwords,
• product descriptions,
• and transaction details.

Strings are essential in nearly every software application.

3.5 Key Notes / Summary

• Strings store text in Java.
• Strings use the String class.
• Strings are reference data types.
• The + operator concatenates strings.
• String methods simplify text processing.
• equals() compares string values.
• Strings are immutable in Java.