New String Data Type

Main.java

import java.util.*;

class Main {
	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		MString ms = new MString("Unassigned");

		System.out.print("Do you want to initialize MString through length (Y/N) : ");
		if( sc.next().toUpperCase().toCharArray()[0] == 'Y') {
			System.out.print("Approximate size of your MString : ");
			int len = sc.nextInt();
			ms = new MString(len);
			System.out.print("Enter desired string : ");
			String input_string_append = sc.next();
			ms.append(input_string_append);
		} else {
			System.out.print("Enter desired string : ");
			String input_string = sc.next();
			ms = new MString(input_string);
		}

		while (true) {
			System.out.println("\nPlease read the instructions.");
			System.out.println("Select the number to perform the required operations.");
			// length()
			System.out.println("1. To Calculate the length of the string.");
			// charAt(int desired_index)
			System.out.println("2. To return the character at given index.");
			System.out.println("3. To convert the string into uppercase.");
			System.out.println("4. To replace character at given index.");
			System.out.println("5. To compare two MStrings.");
			System.out.println("6. To append a character.");
			System.out.println("7. To append a string.");
			System.out.println("8. To insert character at given index.");
			System.out.println("9. To display the string.");
			System.out.println("\nPress any other character to exit.");

			System.out.println("\nEnter respective number for operations.");
			int selection = sc.nextInt();
			switch (selection) {
			case 1:
				System.out.println("Length : " + ms.length());
				break;
			case 2:
				System.out.print("Enter the index to return respective character : ");
				int return_index = sc.nextInt();
				System.out.println("Character in Index " + return_index + " : " + ms.charAt(return_index));;
				break;
			case 3:
				System.out.println("The uppercased string : " + ms.toUpperCase());
				break;
			case 4:
				System.out.print("Enter the index to replace the character : ");
				int index_replacement = sc.nextInt();
				System.out.print("Enter the character as replacement : ");
				ms.replaceCharAt(index_replacement, sc.next().toCharArray()[0]);
				break;
			case 5:
				System.out.print("Enter another string to compare : ");
				System.out.println("Comparision Result : " + ms.equals(new MString(sc.next())));
				break;
			case 6:
				System.out.print("Enter character to append : ");
				ms.append(sc.next().toCharArray()[0]);
				System.out.print("After Appending : ");
				ms.display();
				break;
			case 7:
				System.out.print("Enter string to append : ");
				ms.append(sc.next());
				System.out.print("After Appending : ");
				ms.display();
				break;
			case 8:
				System.out.print("Enter index to insert the character : ");
				int index_insertion = sc.nextInt();
				System.out.print("Enter character to be inserted : ");
				ms.insert(sc.next().toCharArray()[0], index_insertion);
				System.out.print("After Insertion : ");
				ms.display();
				break;
			case 9:
				ms.display();
				break;
			default:
				break;
			}
		}
	}
}

MString.java

import java.lang.String;
// import java.util.Arrays;

public class MString {
	private char[] theChars;
	private int n;

	private void expand(int mustHaveCapacity) {
		char[] temp = new char[2 * mustHaveCapacity];
		System.out.println("Temp size : " + temp.length);
		for (int i = 0; i < this.length(); i++) {
			temp[i] = this.theChars[i];
		}
		this.theChars = temp;
		System.out.println("theChars size : " + this.theChars.length);

		System.out.println("inside expand");
		// this.theChars = Arrays.copyOf(this.theChars, 2*mustHaveCapacity);
	}

	public MString(int desired_length) {
		try {
			this.n = desired_length;
			char[] theChars = new char[n];
			System.out.println("char array created.");

		} catch (NullPointerException e) {
			System.out.println("array is empty");
		}
	}

	public MString(String input_text) {

		n = 1000;
		theChars = new char[n];
		char[] temp = input_text.toCharArray();
		// No Minus 1
		for (int i = 0; i < temp.length; i++) {
			theChars[i] = temp[i];
		}
	}

	public int length() {
		int i = 0;
		while (i < this.n) {
			if(theChars == null) {
				return 0;
			}
			if (theChars[i] == '\0') {
				break;
			}
			i++;
		}

		return i;
	}

	public char charAt(int desired_index) {
		return theChars[desired_index];
	}

	public String toUpperCase() {
		return (new String(theChars)).toUpperCase();
	}

	public void replaceCharAt(int index, char ch) {
		theChars[index] = ch;
	}

	public boolean equals(MString other) {
		boolean assumption = true;
		char[] other_chars = other.theChars;
		int other_length = other.length();
		if (this.length() != other_length) {
			assumption = false;
			return assumption;
		}
		for (int i = 0; i < other_length; i++) {
			if (this.theChars[i] != other_chars[i]) {
				assumption = false;
				return assumption;
			}
		}

		return assumption;
	}

	public void append(char ch) {

		if (this.length() >= this.n) {
			System.out.println("Length before Expanding : " + this.n);
			expand(100);
			System.out.println("Length after Expanding : " + this.n);
		}

		// The last character was stored in length-1. Hence we append the character at
		// index:length.
		this.theChars[this.length()] = ch;
	}

	public void append(String str) {

		// if (this.length() >= this.n) {
		// expand(this.n);
		// }

		char[] str_char_array = str.toCharArray();
		int start_index = this.length();
		for (int i = 0; i < str.length(); i++) {
			this.theChars[start_index] = str_char_array[i];
			start_index++;
		}
	}

	public void insert(char character, int index) {

		// if (this.length() >= this.n) {
		// expand(this.n);
		// }

		int loop_limit = this.length();
		for (int i = loop_limit; i > index; i--) {
			this.theChars[i] = theChars[i - 1];
		}
		this.theChars[index] = character;
	}

	public void display() {
		try {
			int i = 0;
			while (i < this.n) {
				if (this.theChars[i] == '\0') {
					break;
				}
				System.out.print("" + this.theChars[i]);
				i++;

			}
			System.out.println();

		} catch (Exception exc) {
			System.out.println("\nDisplay Error");
		}
	}

}