System.in that allows you
* to more easily read input in a formatted manner. It offers public methods like
* like readLine, readInteger, readDouble,
* etc., each in two versions: one that allows you to specify a default response
* and one without it. If the default response is non-null, it is printed in []
* at the end of the prompt to indicate to the user what the default value is.
* If the user enters no response, the default response is substituted
* and processed instead. All of the methods are static, so you just send
* messages to the SimpleInput class itself, like this:
*
*
* String name = SimpleInput.readLine("What is your name?");
* Date date = SimpleInput.readDate("Please enter a date", "1/1/99");
*
* For those methods that require a particular type of input (integer, * Y/N, etc.) the method will read a full line and attempt to parse the * correct type out, if ill-formatted, the user is chastised and prompted * to enter again. * *
You are free to edit or extend this class, but we don't expect that
* you should need to make any changes.
*
*
* @see java.io.InputStream
* @see java.io.Reader
* @see java.io.BufferedReader
* @version 1.1 01/10/99
* @author Julie Zelenski
*/
public class SimpleInput
{
/**
* Prompts user by printing prompt (without adding a newline) and
* reads entire line of input, up to, but not including the newline.
* If the default response is non-null, it is printed in [] at the
* end of the prompt to indicate to the user what the default value
* is. If the user enters no response, the default response is substituted
* and returned instead. Returns null if I/O failure. Also available
* below in an overloaded version with no default response that returns
* exactly what the user typed, even if the empty string. If you want
* no prompt printed, just pass the "" as the prompt.
* @param prompt string to print to System.out to instruct user
* @param defaultResponse string to substitute for empty response.
* @return the response entered by user (or default if present and
* substituted because user entered nothing.)
*/
public static String readLine(String prompt, String defaultResponse)
{
return promptedReadLine(prompt, defaultResponse);
}
/**
* Calls readLine, passing null for default response.
* @see SimpleInput#readLine(java.lang.String, java.lang.String)
*/
public static String readLine(String prompt)
{
return readLine(prompt, null);
}
/**
* Prompts user by printing prompt (without trailing newline) and
* reads line of input and tries to parse an int out of it by
* using the Integer wrapper class. If Integer couldn't parse it,
* prints an error message and prompts the user to re-enter.
* Does this until user enters a valid integer. The defaultResponse
* in this case should be a string to substitute if the user doesn't
* enter any text. Also available in a version with no parameters without
* a default response. Valid integer format is a sequence of digits
* with optional sign at front.
* @param prompt string to print to System.out to instruct user
* @param defaultResponse string to substitute for empty response.
* @return the integer entered by user (or default if present and
* substituted because user entered nothing.)
*/
public static int readInteger(String prompt, String defaultResponse)
{
while (true) {
String response = promptedReadLine(prompt, defaultResponse);
try { // throws exception if can't parse
return Integer.valueOf(response.trim()).intValue();
}
catch(NumberFormatException e) {
System.out.println("Not an integer. Please re-enter. ");
}
}
}
/**
* Calls readInteger, passing null for default response.
* @see SimpleInput#readInteger(java.lang.String, java.lang.String)
*/
public static int readInteger(String prompt)
{
return readInteger(prompt, null);
}
/**
* Prompts user by printing prompt (without trailing newline) and
* reads line of input and tries to parse a double out of it by
* using the Double wrapper class. If Double couldn't parse it,
* prints an error message and prompts the user to re-enter.
* Does this until user enters a valid double. The defaultResponse
* in this case should be a string to substitute if the user doesn't
* enter any text. Also available in a version with no parameters without
* a default response. Double class accepts most reasonable formats
* (with or without decimal leading zero, sign, etc.) but rejects those
* with non-numeric components, extra decimal points, etc.
* @param prompt string to print to System.out to instruct user
* @param defaultResponse string to substitute for empty response.
* @return the double entered by user (or default if present and
* substituted because user entered nothing.)
*/
public static double readDouble(String prompt, String defaultResponse)
{
while (true) {
String response = promptedReadLine(prompt, defaultResponse);
try { // throws exception if can't parse
return Double.valueOf(response.trim()).doubleValue();
}
catch(NumberFormatException e) {
System.out.println("Not a double value. Please re-enter. ");
}
}
}
/**
* Calls readDouble, passing null for default response.
* @see SimpleInput#readDouble(java.lang.String, java.lang.String)
*/
public static double readDouble(String prompt)
{
return readDouble(prompt, null);
}
/**
* Prompts user by printing prompt (without trailing newline) and
* reads line of input and checks if first character is Y or N
* and returns boolean accordingly. If response doesn't match,
* prints an error message and prompts the user to re-enter.
* Does this until user enters something that begins with Y or N.
* Also available in a version with no default response.
* @param prompt string to print to System.out to instruct user
* @param defaultResponse string to substitute for empty response.
* @return true if user entered Y, false for N
*/
public static boolean readYesOrNo(String prompt, String defaultResponse)
{
while (true) {
String response = promptedReadLine(prompt, defaultResponse);
if (response.length() > 0) {
switch (Character.toUpperCase(response.charAt(0))) {
case 'Y': return true;
case 'N': return false;
default: System.out.println("Not a valid response. Please enter Y or N.");
}
}
}
}
/**
* Calls readYesOrNo, passing null for default response.
* @see SimpleInput#readYesOrNo(java.lang.String, java.lang.String)
*/
public static boolean readYesOrNo(String prompt)
{
return readYesOrNo(prompt, null);
}
/**
* Prompts user by printing prompt (without trailing newline) and
* reads line of input and tries to parse a data out of it by
* using the Convert class. If string cannot be converted into
* a valid date, we print an error message and prompt the user to re-enter.
* Does this until user enters a valid date. Also available in a
* version with no default response. The expected format for dates
* is m/d/y.
* @param prompt string to print to System.out to instruct user
* @param defaultResponse string to substitute for empty response.
* @return the date entered by user (or default if present and
* substituted because user entered nothing.)
* @see Convert
*/
public static Date readDate(String prompt, String defaultResponse)
{
while (true) {
String response = promptedReadLine(prompt, defaultResponse);
Date d = Convert.stringToDate(response, "M/d/y");
if (d != null) return d;
System.out.println("Improper date, please re-enter (m/d/y expected). ");
}
}
/**
* Calls readDate, passing null for default response.
* @see SimpleInput#readDate(java.lang.String, java.lang.String)
*/
public static Date readDate(String prompt)
{
return readDate(prompt, null);
}
/**
* Main internal helper to print prompt and read entire line of
* text from BufferedReader operating on System.in. On an
* I/O exception, it returns null.
*/
private static String promptedReadLine(String prompt, String defaultResponse)
{
try {
System.out.print(prompt);
if (defaultResponse != null) // if there is a default, append in brackets
System.out.print(" [" + defaultResponse + "]: ");
String response = reader.readLine().trim();
if ((response == null || response.equals("")) && defaultResponse != null)
response = defaultResponse; // substitute default for empty string
return response;
}
catch(java.io.IOException e) {
return null;
}
}
private static BufferedReader reader;
static {
reader = new BufferedReader(new InputStreamReader(System.in));
}
}