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

LESSON-7 STRINGS IN JAVA

Strings (String class & 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)

---

✅ String Declaration Methods

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

---

✅ 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);

---

✅ 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)

---

✅ 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

---

✅ 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 ✔

---

📝 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 ✅🔥

---

🎯 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 → ?

---

✅ Lesson-7 Part-1 Completed!

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