Java Programming Lesson 7 Part-1 | String class & methods for Beginners

LESSON-7 STRINGS IN JAVA

Strings (String class & methods) 

Welcome to Lesson 7 Part-1 of the Java Programming Series!

In this lesson, you will learn about the String class — one of the most commonly used and most powerful classes in the Java programming language.

Strings are everywhere: names, messages, inputs, file paths, text data, user responses, and more. That’s why mastering the String class and its essential methods is crucial for beginners.

This lesson explains what strings are, how they work in Java, and how to manipulate them using built-in methods.

✅ What is String?

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

Example:

String name = "Java";

Property ✅

✔ String is immutable (cannot be changed once created)

✅ Why Strings Are Important

Strings are used for:

• User input
• Messages and labels
• File names and file paths
• Data processing
• API communication
• Text formatting
• UI messages
• Console interaction

Almost every program uses strings!

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✅ String Declaration Methods

String s1 = "Hello";               // Recommended
String s2 = new String("World");   // Object form

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✅ String Input from User

Scanner sc = new Scanner(System.in);
System.out.print("Enter your name: ");
String name = sc.nextLine();
System.out.println("Welcome " + name);

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✅ Most Important String Methods

Method	Meaning	Example Output
length()	Count characters	"Java".length() → 4
toUpperCase()	Convert to capital	"java".toUpperCase()
toLowerCase()	Convert to small	"HELLO".toLowerCase()
charAt(i)	Get character	"Java".charAt(1) → 'a'
equals()	Compare strings	"A".equals("a") → false
contains()	Substring present?	"coding".contains("cod")
replace()	Replace characters	"java".replace('a','o')
substring()	Cut part	"Hello".substring(1,4)

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✅ Practical Example

public class StringExample {
    public static void main(String[] args) {

        String s = "Java Programming";

        System.out.println("Length: " + s.length());
        System.out.println("Uppercase: " + s.toUpperCase());
        System.out.println("Character at index 5: " + s.charAt(5));
        System.out.println("Contains 'Program': " + s.contains("Program"));
        System.out.println("Substring(5, 16): " + s.substring(5, 16));
    }
}

✅ Output:

Length: 16
Uppercase: JAVA PROGRAMMING
Character at index 5: P
Contains 'Program': true
Substring(5, 16): Programming

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✅ Compare Strings: equals() vs ==

String a = "Java";
String b = "Java";
String c = new String("Java");

System.out.println(a == b);        // true (same memory pool)
System.out.println(a == c);        // false
System.out.println(a.equals(c));   // true (same content)

📌 Use equals() to compare text values ✔

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📝 Exercise for You ✅

Create a String program:

Input from user:

✅ Full Name

Program should:
✔ Print total characters
✔ Print uppercase version
✔ Print first character
✔ Check whether name contains "a" or "A"

Example Output:

Enter Name: Jitu Hasan
Total Characters: 10
Uppercase: JITU HASAN
First Letter: J
Contains 'a'? true

Reply with your:
✅ Code
✅ Output

I’ll check & give grading ✅🔥

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🎯 Quick Quiz

1️⃣ String is:
A) Primitive
B) Non-Primitive

2️⃣ Which method compares text values?
A) ==
B) equals()
C) compare()

Reply like:
1 → ?, 2 → ?

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⭐ Conclusion In Java Lesson 7 Part-1, you learned:

✔ What strings are

✔ How to create and use them

✔ Why strings are immutable

✔ Most useful String methods

✔ How to split, search, modify, and compare strings

✔ A mini practice project

Strings are a fundamental skill in Java. Mastering them now will help you tremendously in topics like:

• Input parsing
• File handling
• OOP
• Data processing
• Algorithms

✅ Lesson-7 Part-1 Completed!

➡ NEXT Lesson-7 Part-2: Functions/Methods

Frequently Asked Questions (FAQs)

What is a method or function in Java?

A method is a block of code that performs a specific task. Methods help make code reusable, organized, and easier to maintain.

Why should we use methods in Java?

Methods reduce code duplication, improve readability, split complex programs into smaller parts, and make debugging easier.

What is the basic structure of a Java method?

A method usually consists of: return type → method name → parameters → method body.

What is the difference between parameters and arguments?

Parameters are variables defined in the method, while arguments are the actual values passed to the method when it is called.

What is a void method?

A void method does not return any value. It performs a specific action without producing a return value.

What is method overloading?

Method overloading is when multiple methods share the same name but have different parameter lists, allowing flexibility in method calls.

What is the purpose of the return keyword?

The return keyword sends a value from a method back to the caller and ends the method execution.

Where are methods defined in Java?

All methods are defined inside a class because Java is a fully object-oriented programming language.