Valid User Input

//Ask for the users name
String name = Console.readString("Enter your name:");
 
//Ask for the users age (between 6 and 110)
int age = Console.readInteger("Enter you age:", "You cannot be that old!", 6, 110);
 
//Ask for a float
float pay = Console.readFloat("How much do you earn per hour:");
 
//Ask for a double
double pi = Console.readDouble("Enter as many digits of PI as you can remember:");
 
//Ask a yes/no question
boolean isProgrammer = Console.readYesNo("Are you a programmer [YES or NO]:");
 
//Ask for an integer with the default prompt
int i0 = Console.readInteger();
 
//Ask for an integer with a custom prompt
int i1 = Console.readInteger("Enter a number: ");
 
//Ask for an integer with a custom prompt and custom error message
int i2 = Console.readInteger("Enter a number: ", "Try again.");
 
//Ask for an integer in the range 1..10 with a custom prompt and custom error message 
int i3 = Console.readInteger("Enter a number between 1 and 10", "Not in range.", 1, 10);
 
//Ask if the user would like to quit (put this in an infinite loop)
if (Console.readYesNo("Really Quit [y/n]")) { System.exit(0); }

 
import java.io.IOException;
 
/**
 * Console.java
 * 
 * This class is a convinence wrapper for the common task of
 * asking for user input. Features include:
 *      - recusive input validation for all primitive types
 *      - overloaded methods for lazy usage or informative prompting
 *	 - consistant, meaningful prompting behaviour
 *
 *      
 * 
 *  Some usages: 
 *      - int i1 = Console.readInteger("Enter a number: ");
 *      - int i2 = Console.readInteger("Enter a number: ", "Try again.");
 *      - int i3 = Console.readInteger("Enter a number between 1 and 10", "Not in range.", 1, 10);
 *      - float f = Console.readFloat("Enter a decimal number: ");
 *      - if (Console.readYesNo("Really Quit [y/n]")) { System.exit(0); }
 *      
 * 
 * @author Christopher Lowe 
 * @version 5/4/2011
 * 
 */
public class Console
{
 
	private static final String CONSOLE = "> ";
	private static final String DEFAULT_PROMPT = "Enter input: ";
	private static final String DEFAULT_RETRY = "Invalid Input. Try again.";
 
 
	/**
	 * Prompts the user for a YES/NO input. It will default to false on incorrect input.
	 *
	 * @param prompt The message asking for user input
	 * @return true if the user inputs "Y", "y", "yes", "YES" or "YeS"
	 */
	public static final boolean readYesNo(String prompt) {
		String input = readLine(prompt).toLowerCase().trim();
		if (input.equals("yes") || input.equals("y")) {
			return true;
		}
		//Behavioural: only a discrete 'yes' will return true.
		//It does not recurse on invalid input because incorrect input
		//is logically identical to the non-destructive 'no'
		return false;
	}
 
	/**
	 * Prompts the user for YES/NO input. It will default to false on incorrect input.
	 *
	 * @return true if the user inputs "Y", "y", "yes", "YES" or "YeS"
	 */
	public static final boolean readYesNo() {
		return readYesNo(DEFAULT_PROMPT);
	}
 
	/**
	 * Prompts the user for YES/NO input. It will default to false on incorrect input.
	 *
	 * @param prompt The message asking for user input
	 * @return true if the user inputs "Y", "y", "yes", "YES" or "YeS"
	 */
	public static final boolean readBoolean(String prompt) {
		return readYesNo(prompt);
	}
 
	/**
	 * Prompts the user for YES/NO input. It will default to false on incorrect input.
	 *
	 * @return true if the user inputs "Y", "y", "yes", "YES" or "YeS"
	 */	 
	public static final boolean readBoolean() {
		return readYesNo(DEFAULT_PROMPT);
	}
 
 
	/**
	 * Prompts the user for an Integer input in a given range.
	 *
	 * @param prompt The message asking for user input.
	 * @param error The error message to inform the user that the input was invalid.
	 * @param min The minimum valid input
	 * @param max The maximum valid input
	 * @return An integer in the range min..max
	 */
	public static final int readInteger(String prompt, String error, int min, int max) {
		if (min >= max) {
			return 0;   //Should not happen, but can if the client programmer is not paying attention
		}
 
		try {
			int i = Integer.valueOf((readLine(prompt)));
			if ((i < min) || (i > max)) {
				System.out.println(error);
				return readInteger(prompt, error, min, max);
			}
			return i;
		} catch (NumberFormatException e) {
			System.out.println(error);
			return readInteger(prompt, error, min, max);
		}
	}
 
 
	/**
	 * Prompts the user for an Integer input in a given range.
	 *
	 * @param prompt The message asking for user input.
	 * @param min The minimum valid input.
	 * @param max The maximum valid input.
	 * @return An integer in the range min..max
	 */
	public static final int readInteger(String prompt, int min, int max) {
		return readInteger(prompt, DEFAULT_RETRY, min, max);
	}
 
 
	/**
	 * Prompts the user for an Integer input in a given range.
	 *
	 * @param min The minimum valid input.
	 * @param max The maximum valid input.
	 * @return An integer in the range min..max
	 */
	public static final int readInteger(int min, int max) {
		return readInteger(DEFAULT_PROMPT, DEFAULT_RETRY, min, max);
	}
 
 
	/**
	 * Prompts the user for an Integer input.
	 *
	 * @param prompt The message asking for user input.
	 * @param error The error message to inform the user that the input was invalid.
	 * @return An integer
	 */
	public static final int readInteger(String prompt, String error) {
		try {
			return Integer.valueOf((readLine(prompt)));
		} catch (NumberFormatException e) {
			System.out.println("\n" + error);
			return readInteger(prompt, error); 
		}
	}
 
 
	/**
	 * Prompts the user for an Integer input.
	 *
	 * @param prompt The message asking for user input.
	 * @return An integer
	 */
	public static final int readInteger(String prompt) {
		return readInteger(prompt, DEFAULT_RETRY);
	}
 
 
	/**
	 * Prompts the user for an Integer input.
	 *
	 * @return An integer
	 */
	public static final int readInteger() {
		return readInteger(DEFAULT_PROMPT, DEFAULT_RETRY);
	}
 
 
	/**
	 * Prompts the user for a Double input.
	 * 
	 * @param prompt The message asking for user input.
	 * @param error The message to inform the user about invalid input.
	 * @return A double
	 */
	public static final double readDouble(String prompt, String error) {
		try {
			return Double.valueOf((readLine(prompt)));
		} catch (NumberFormatException e) {
			System.out.println("\n" + error);
			return readDouble(prompt, error);
		}
	}
 
	/**
	 * Prompts the user for a Double input.
	 * 
	 * @param prompt The message asking for user input.
	 * @return A double
	 */
	public static final double readDouble(String prompt) {
		return readDouble(prompt, DEFAULT_RETRY);
	}
 
	/**
	 * Prompts the user for a Double input.
	 * 
	 * @return A double
	 */
	 public static final double readDouble() {
		return readDouble(DEFAULT_PROMPT, DEFAULT_RETRY);
	 }
 
 
	/**
	 * Prompts the user for a Float input.
	 *
	 * @param prompt The message asking for input.
	 * @param error The message informing the user that the input was invalid.
	 * @return A float
	 */
	public static final float readFloat(String prompt, String error) {
		try {
			return Float.valueOf((readLine(prompt)));
		} catch (NumberFormatException e) {
			System.out.println("\n" + error);
			return readFloat(prompt, error);
		}
	}
 
 
	/**
	 * Prompts the user for a Float input.
	 *
	 * @param prompt The message asking for input.
	 * @return A float
	 */
	public static final float readFloat(String prompt) {
		return readFloat(prompt, DEFAULT_RETRY);
	}
 
 
	/**
	 * Prompts the user for a Float input.
	 *
	 * @return A float
	 */
	public static final float readFloat() {
		return readFloat(DEFAULT_PROMPT, DEFAULT_RETRY);
	}
 
	/**
	 * Prompts the user for a String input at least minLength in size.
	 *
	 * @param prompt The message asking for user input.
	 * @param error The message informing the user about invalid input
	 * @param minLength The minimum length of the string that is valid
	 * @return A string minLength or greater in length
	 */
	public static final String readString(String prompt, String error, int minLength) {
		String input = readLine(prompt);
		if (input.length() < minLength) {
			System.out.println("\n" + error);
			return readString(prompt, error, minLength);
		}
 
		return input;
	}
 
 
	/**
	 * Prompts the user for a String input. It will prompt again if the user does not enter anything
	 *
	 * @param prompt The message asking for user input.
	 * @param error The message informing the user of invalid input
	 * @return A String
	 */
	public static final String readString(String prompt, String error) {
		String input = readLine(prompt);
		if ((input.length() == 0) || (input == null) || (input.equals("\n"))) {
			System.out.println("\n" + error);
		}
 
		return input;		
	}
 
 
	/**
	 * Prompts the user for a String input.
	 *
	 * @param prompt The message asking for user input.
	 * @return A String
	 */
	public static final String readString(String prompt) {		
		return readString(prompt, DEFAULT_RETRY);
	}
 
 
	/**
	 * Prompts the user for a String input.
	 *
	 * @return A String
	 */
	public static final String readString() {
		return readString(DEFAULT_PROMPT, DEFAULT_RETRY);
	}
 
 
 
	/**
	 *  Working method, used by every single method in this class.
	 *  It uses the low level System.in.read() to build a StringBuffer containing
	 *  the users input and traps the user in an loop until ENTER is pressed.
	 *  In windows, the ENTER button returns /r/n which is dealt with in the loop.
	 */
	private static final String readLine(String prompt) {
		System.out.print(prompt);
		System.out.print("\n");
		System.out.print(CONSOLE);
 
		StringBuffer b = new StringBuffer();
		while(true) {
			try {
				char c = (char) System.in.read();
				b.append(c);
				if (c == '\n') {
					return b.toString().trim();    //Enter pressed
				} else if (c == '\r') { }   //Windows carriage return \r is followed by \n so we ignore it and pick it up on the next loop
			} catch (IOException e) { }     //Unsure what would cause this and what to do about it
		}
	}
}