Problem

(FROM COMSCI CONTEST 2010)
In non-smart cell phones, text input can be handled by a technique called multi-tap(example picture: link here). With multi-tap, you use the letters on each key, and press a key multiple times to access different letters. For instance, to get the letter 'a', you press the 2 key once, but to get 'n', you press the 6 key twice (the first press gives you 'm', the second switches 'm' to 'n'). A slight pause by the user will indicate the end of inputting one character and a beginning of the input of the next character. The letters 'q' and 'z', not originally part of the letters on a phone, force the keys 7 and 9 to have four characters each. All other keys have 3 characters.
Write a program which, given a word (a string of upper case letters with no spaces), outputs the sequence of keystrokes using multi-tap. If a key is pressed multiple times, it should appear that many times in the input. A pause is indicated by a single space.
Examples:

 Enter code: 222666 67777222444
Translated Code: COMSCI
Enter code: 7 2 777 2 7777 444 8 444 222
Translated Code: PARASITIC 

This problem will cover the following topics:

• If and nested if statements
• Arrays
• Scanner
• System.out
• Modulus
• While loops

...By Students

"COMP 1010 is where I first learned how to make a program. I was only taking that course for prerequisite and do not have interest on it, but as time goes by, I notice that I was enjoying myself making a program.

I learned that commenting important parts of the code really helps a lot especially to myself since I can track down why I did that code. Also, if you want to check or want to debug your code, try commenting out the parts you don't need yet and try to output some parts of the code to see what your code is doing. And the last but not the least. Don't do all the coding in one shot, it will take you more time to debug it than running the program while the coding is still small."

Solution

Start by importing the swing java package.

 import javax.swing.*;
import java.util.Scanner; 

Next is to think all the step necessary for the program to work.

• Get user input
• Check if the input are all numbers or numbers with spaces
• Process the input and change them to letters

Note: This solution will show 3 method to do all these steps to make the program look neat. You can always put all codes in main but it will be messy

First to get the Input of the user.
In order to get the user input, you have to use the Scanner's method .nextLine() in order to get the whole input. Since you do not know the when user will stop, you have to put the scanner inside a while loop. You also want to check validation of the input but let another method handle the validation. If input is not valid, output an error message to alert the user.

 Scanner scan = new Scanner(System.in);  // To enter the input
String input = " ";                     // Store the input
String convert = "";	                // Store the translated input
System.out.print("Enter code: ");

while(!input.equals(""))
{
	input = scan.nextLine();         // scan will get the user input and store in in the String input

	if(checkInput(input))            // calls the method checkInput to check for validation
	{
		convert = codeEncription(input);                 //calls the method codeEcription to translate the input into letters
		System.out.print("Translated Code: "+convert);   //output message
		System.out.print("\nEnter code: ");
		}
	else
	{
		System.out.println("Invalid Input");              //error message
		System.out.print("Enter code: ");
	}

} 

 Enter code: 23a43
Invalid Input
Enter code: 77 88 444 9999 9999 444 222 2 555
Translated Code: QUIZZICAL 

Next is to make a method that will validate the user input.It will have a String as a parameter to pass the input to this method
You have to check each character in the input to see if there is an invalid input. While loops is still necessary for this task since you don't know if you will find an error or not in the input. This method will return true if its valid or false if invalid.

 public static boolean checkInput(String input)
{
	boolean check = true;
	int counter = 0;

	while( check && counter < input.length())  
	{
		if(input.charAt(counter) == ' ')        //if space is found in the input its still valid
			counter++;
		else if(input.charAt(counter) < '0' || input.charAt(counter) > '9')  //check if its a number or not
			check = false;
		else
			counter++;
	}

	return check;     //returns true if valid or false if not valid
} 

Next step is to make a method that will translate the input.It has String as a parameter as well.
In order to translate the input, you have to check each character in the String. This means you can use for loops in this method since you will know went exactly to stop. Every time you check a character, store the current character and count how many are there after the current character change. Then pass the current character and the number of count you had to another method what will change the number into Letters

 public static String codeEncription(String input)
{
	String output = "";             //Store each number that is translated into letter
	int counter = 1;                //count the number of same consecutive number
	char last = input.charAt(0);    //Initialize the last to the first character of the string
	char cur = input.charAt(0);     //Initialize the cur to the first character of the string
	for(int i = 1 ; i <= input.length();i++)
	{
		if(i < input.length())             
		{
			cur = input.charAt(i);     //store the current character to cur
		}
		else
		{
			cur = '.';                  //this else statement is necessary to complete the last letter of the input
		}

		if(cur == last)
		{
			counter++;                   //number of same consecutive number
		}
		else
		{

			output += converter(last,counter) +"";  //this will call converter() method that will change the number into letter
			last = cur;                             //to set the last into the current character
			counter = 1;
		}
	}
	return output;                                           // return the translated code
} 

Last step is to make a method that will convert the number into letter using String array and Modulus.
In this method, there are two parameter ,char and int, the char represent the number and the in represent how many consecutive number was found in the current search from the other method. This will return the equivalent letter or if its space it will return empty String.

 public static String converter(char find,int count)
{
        //String array are manually entered. The arrangement of letters is necessary in order to get the right letter
	String[] two = {"C","A","B"};
	String[] three = {"F","E","D"};
	String[] four = {"I","G","H"};
	String[] five = {"L","J","K"};
	String[] six = {"O","M","N"};
	String[] seven = {"S","P","Q","R"};
	String[] eight = {"V","T","U"};
	String[] nine = {"Z","W","X","Y"};
	String convert = "";

        //doing a modulus will return either 1,2 or 0 if its mod 3 and 1,2,3 or 0 if its mod 4
	if(find == '2'){
		convert = two[(count%3)];
	}else if(find == '3')
	{
		convert = three[(count%3)];
	}else if(find == '4')
	{
		convert = four[(count%3)];
	}else if(find == '5')
	{
		convert = five[(count%3)];
	}else if(find == '6')
	{
		convert = six[(count%3)];
	}else if(find == '7')
	{
		convert = seven[(count%4)];
	}else if(find == '8')
	{
		convert = eight[(count%3)];
	}else if(find == '9')
	{
		convert = nine[(count%4)];
	}

	return convert;
} 

This program will helps you how to make a clean code and make sure you make it simple as possible.

Code

Solution Code

import java.util.Scanner;
import javax.swing.*;

public class CellText
{
    public static void main(String[] args)
    {
        	Scanner scan = new Scanner(System.in);  // To enter the input
		String input = " ";                     // Store the input
		String convert = "";	                // Store the translated input
		System.out.print("Enter code: ");

		while(!input.equals(""))
		{
			input = scan.nextLine();         // scan will get the user input and store in in the String input

			if(checkInput(input))            // calls the method checkInput to check for validation
			{
				convert = codeEncription(input);                 //calls the method codeEcription to translate the input into letters
				System.out.print("Translated Code: "+convert);   //output message
				System.out.print("\nEnter code: ");
				}
			else
			{
				System.out.println("Invalid Input");              //error message
				System.out.print("Enter code: ");
			}

		}


    }

	public static boolean checkInput(String input)
	{
		boolean check = true;
		int counter = 0;

		while( check && counter < input.length())  
		{
			if(input.charAt(counter) == ' ')        //if space is found in the input its still valid
				counter++;
			else if(input.charAt(counter) < '0' || input.charAt(counter) > '9')  //check if its a number or not
				check = false;
			else
				counter++;
		}

		return check;     //returns true if valid or false if not valid
	}

	public static String codeEncription(String input)
	{
		String output = "";             //Store each number that is translated into letter
		int counter = 1;                //count the number of same consecutive number
		char last = input.charAt(0);    //Initialize the last to the first character of the string
		char cur = input.charAt(0);     //Initialize the cur to the first character of the string
		for(int i = 1 ; i <= input.length();i++)
		{
			if(i < input.length())             
			{
				cur = input.charAt(i);     //store the current character to cur
			}
			else
			{
				cur = '.';                  //this else statement is necessary to complete the last letter of the input
			}

			if(cur == last)
			{
				counter++;                   //number of same consecutive number
			}
			else
			{

				output += converter(last,counter) +"";  //this will call converter() method that will change the number into letter
				last = cur;                             //to set the last into the current character
				counter = 1;
			}
		}
		return output;                                           // return the translated code
	}


	public static String converter(char find,int count)
	{
			//String array are manually entered. The arrangement of letters is necessary in order to get the right letter
		String[] two = {"C","A","B"};
		String[] three = {"F","E","D"};
		String[] four = {"I","G","H"};
		String[] five = {"L","J","K"};
		String[] six = {"O","M","N"};
		String[] seven = {"S","P","Q","R"};
		String[] eight = {"V","T","U"};
		String[] nine = {"Z","W","X","Y"};
		String convert = "";

			//doing a modulus will return either 1,2 or 0 if its mod 3 and 1,2,3 or 0 if its mod 4
		if(find == '2'){
			convert = two[(count%3)];
		}else if(find == '3')
		{
			convert = three[(count%3)];
		}else if(find == '4')
		{
			convert = four[(count%3)];
		}else if(find == '5')
		{
			convert = five[(count%3)];
		}else if(find == '6')
		{
			convert = six[(count%3)];
		}else if(find == '7')
		{
			convert = seven[(count%4)];
		}else if(find == '8')
		{
			convert = eight[(count%3)];
		}else if(find == '9')
		{
			convert = nine[(count%4)];
		}

		return convert;
	}
}