Strings in Java

// String literal (String pool मध्ये)
String name = "Rahul";
String city = "Pune";

// new keyword (heap मध्ये — avoid करा)
String s = new String("Hello");

// Concatenation
String full = name + " from " + city;
System.out.println(full);   // Rahul from Pune

// concat() method
String greeting = "नमस्कार ".concat(name);
System.out.println(greeting);  // नमस्कार Rahul

// String + number — auto convert होतो
int age = 20;
System.out.println(name + " is " + age + " years old.");

String s = "  Hello World  ";

// Length
System.out.println(s.length());         // 15

// Case
System.out.println(s.toUpperCase());    // "  HELLO WORLD  "
System.out.println(s.toLowerCase());    // "  hello world  "

// Trim
System.out.println(s.trim());           // "Hello World"

// Substring
String text = "Hello World";
System.out.println(text.substring(6));     // "World"
System.out.println(text.substring(0, 5)); // "Hello"

// indexOf, contains, replace
System.out.println(text.indexOf("World")); // 6
System.out.println(text.contains("Hello")); // true
System.out.println(text.replace("World", "Java")); // Hello Java

// Split
String csv = "Pune,Mumbai,Nagpur";
String[] cities = csv.split(",");
for (String c : cities) System.out.println(c);

// charAt, compareTo
System.out.println(text.charAt(0));          // H
System.out.println("abc".compareTo("abc")); // 0 — equal

String s1 = "Hello";
String s2 = "Hello";
String s3 = new String("Hello");

// == compares references (memory address)
System.out.println(s1 == s2);     // true (String pool)
System.out.println(s1 == s3);     // false! (different objects)

// .equals() compares content — HE VAAPARAA!
System.out.println(s1.equals(s3));         // true ✅
System.out.println(s1.equalsIgnoreCase("hello")); // true

// Loop मध्ये String concatenate करायला StringBuilder वापरा
StringBuilder sb = new StringBuilder();

for (int i = 1; i <= 5; i++) {
    sb.append("Item ").append(i).append("\n");
}

sb.insert(0, "--- Shopping List ---\n");
sb.delete(sb.length() - 1, sb.length());  // last \n काढा

System.out.println(sb.toString());
System.out.println("Length: " + sb.length());