Notes

public class Main {
public static void main(String[] args) {
String str = "Hello World!";

// length() method returns the number of characters in a string
int length = str.length();
System.out.println("Length of string: " + length); // 12

// charAt() method returns the character at a specified index
char c = str.charAt(6);
System.out.println("Character at index 6: " + c); // W

// substring() method returns a new string from a specified start and end index
String subStr = str.substring(6, 11);
System.out.println("Substring: " + subStr); // World

// replace() method replaces all occurrences of a specified character or string
String newStr = str.replace("l", "x");
System.out.println("New String: " + newStr); // Hexxo Worxd!

// toUpperCase() method converts a string to uppercase
String upper = str.toUpperCase();
System.out.println("Uppercase: " + upper); // HELLO WORLD!

// toLowerCase() method converts a string to lowercase
String lower = str.toLowerCase();
System.out.println("Lowercase: " + lower); // hello world!

// trim() method removes leading and trailing white spaces
String text = " Hello World! ";
String trim = text.trim();
System.out.println("Trimmed: " + trim); // "Hello World!"

// split() method splits a string into an array of substrings
String[] words = str.split(" ");
for (String word : words) {
System.out.println(word);
}
// Output:
// "Hello"
// "World!"
}
}