post String revision in HINGLISH

qBilkul bhai! Java mein String ek kaafi important topic hai. Main tujhe step-by-step String ke basics se lekar advanced concepts tak revise karwata hoon.

1. String Introduction

  • String ek class hai jo Java mein java.lang.String package ka part hai.
  • String ko immutable bola jata hai, iska matlab hai ek baar string banne ke baad usko change nahi kar sakte.
  • String ko ya to String literals ke through ya phir new keyword se create karte hain.

Example:

// Using String literal
String str1 = "Hello";

// Using new keyword
String str2 = new String("World");

2. Important Methods of String

(a) Length of a String

String ka length nikalne ke liye length() method use hota hai.

String str = "Java";
System.out.println(str.length()); // Output: 4

(b) Concatenation (Join Strings)

Strings ko combine karne ke liye + operator ya concat() method ka use hota hai.

String s1 = "Hello";
String s2 = "World";
System.out.println(s1 + " " + s2);  // Output: Hello World
System.out.println(s1.concat(" " + s2));  // Output: Hello World

(c) Character Extraction

  1. charAt(index) - Kisi specific index ka character nikalta hai.
  2. substring(startIndex, endIndex) - Ek substring nikalta hai.
String s = "Hello";
System.out.println(s.charAt(1)); // Output: e
System.out.println(s.substring(1, 4)); // Output: ell

(d) String Comparison

  1. equals() - Dono strings ka exact match check karta hai.
  2. equalsIgnoreCase() - Case ko ignore karke strings compare karta hai.
  3. compareTo() - Lexicographical comparison karta hai.
String s1 = "Hello";
String s2 = "hello";

// Case-sensitive
System.out.println(s1.equals(s2)); // Output: false

// Case-insensitive
System.out.println(s1.equalsIgnoreCase(s2)); // Output: true

// Lexicographical comparison
System.out.println(s1.compareTo(s2)); // Output: -32

(e) Searching in String

  1. indexOf(char) - Character ka first occurrence batata hai.
  2. lastIndexOf(char) - Character ka last occurrence batata hai.
  3. contains(String) - String ke andar substring check karta hai.
String s = "Java Programming";
System.out.println(s.indexOf('a')); // Output: 1
System.out.println(s.lastIndexOf('a')); // Output: 13
System.out.println(s.contains("Java")); // Output: true

(f) String Replacement

replace(oldChar, newChar) aur replaceAll(regex, replacement) ka use hota hai.

String s = "Java is fun";
System.out.println(s.replace('a', 'e')); // Output: Jeve is fun
System.out.println(s.replaceAll("fun", "awesome")); // Output: Java is awesome

(g) Case Conversion

  1. toUpperCase() - String ko uppercase mein convert karta hai.
  2. toLowerCase() - String ko lowercase mein convert karta hai.
String s = "Hello World";
System.out.println(s.toUpperCase()); // Output: HELLO WORLD
System.out.println(s.toLowerCase()); // Output: hello world

3. Immutable vs Mutable Strings

  • Immutable String: String class immutable hoti hai.
  • Mutable String: StringBuilder aur StringBuffer mutable hote hain.

Example of Immutable:

String s = "Hello";
s.concat(" World");
System.out.println(s); // Output: Hello (original string unchanged)

Example of Mutable (StringBuilder):

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

4. String Pool

  • String literals String Pool mein store hote hain (Heap ke andar ek special memory).
  • Agar ek hi string literal do alag variables mein use ho raha hai, to dono same memory location point karte hain.

Example:

String s1 = "Java";
String s2 = "Java";
System.out.println(s1 == s2); // Output: true

But agar new keyword use karenge to alag memory allocate hoti hai.

String s1 = new String("Java");
String s2 = new String("Java");
System.out.println(s1 == s2); // Output: false
System.out.println(s1.equals(s2)); // Output: true

5. StringTokenizer (for Splitting)

Java mein StringTokenizer ka use string ko split karne ke liye hota hai.

import java.util.StringTokenizer;

StringTokenizer st = new StringTokenizer("Java is fun", " ");
while (st.hasMoreTokens()) {
    System.out.println(st.nextToken());
}
// Output:
// Java
// is
// fun

6. Advanced Topics

  1. String Joiner: Strings ko join karne ke liye.

    import java.util.StringJoiner;

StringJoiner sj = new StringJoiner(", ");
sj.add("Java").add("Python").add("C++");
System.out.println(sj); // Output: Java, Python, C++

  2. String Format: Formatted strings create karna.

    String s = String.format("Name: %s, Age: %d", "Ali", 25);
System.out.println(s); // Output: Name: Ali, Age: 25

  3. [[StringBuilder]] vs [[StringBuffer]]:

    • StringBuilder fast hai but thread-safe nahi hai.
    • StringBuffer slow hai but thread-safe hai.

Yeh tha Java Strings ka ek detailed revision! Agar kisi point mein doubt ho ya code ka example chahiye, to bata de.

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