Added DuplicateChars Java program and updated the README file (#28)

* add: DuplicateChars Java program and updated the README file

* refactor: the code to look nicer and to use static inputs

Co-authored-by: Aarav Arora <[email protected]>

Java/DuplicateChars.java

@@ -0,0 +1,33 @@
+// Check if the given String has duplicate characters, ignoring case.
+public class DuplicateChars {
+
+	public static void main(String[] args) {		
+		String str1 = "duplicate";
+		String str2 = "character";
+
+		System.out.println("'" + str1 + "' contains duplicate characters? " + checkDuplicateChars(str1));
+		System.out.println("'" + str2 + "' contains duplicate characters? " + checkDuplicateChars(str2));
+	}
+
+	static boolean checkDuplicateChars(String str) {
+		// Trim leading and trailing spaces
+		str = str.trim();
+
+		// Convert all the characters in the String to lower case
+		str = str.toLowerCase();		
+
+		// Convert the given string to a char array
+		char[] chars = str.toCharArray();
+
+		// Check each characters present in the string
+		for (int i = 0; i < chars.length; i++) {			
+			for (int j = i + 1; j < chars.length; j++) {
+				if (chars[i] == chars[j]) {					
+					return true; // Found a duplicate character
+				}
+			}			
+		}
+
+		return false; // No duplicate character found		
+	}
+}

README.md

@@ -41,7 +41,8 @@ Language
 ├─ linkedlist.
 ├─ selectionsort.
 ├─ mergesort.
-└─ armstrong_no.
+├─ Armstrong_no.
+└─ duplicatechars.
 
 
 ```