John Powell

In the following program the user has a simple menu with 3 choices. Two choices (a & b) will run specific methods and the final choice will quit the program. Is there a simple way to ask the user to press a key (once the called method is done) to return to the main menu, rather than returning automatically?

import java.util.Scanner; public class TestMenu { public static void main (String [] args) { menu(); } public static void menu() { Scanner kbd = new Scanner( System.in); do { System.out.println("a: Option 1"); System.out.println("b: Option 2"); System.out.println("q: QUIT"); System.out.print("\nSelect an option: "); String input = kbd.next( ); switch (input.charAt(0)) { case 'a': case 'A': start(); break; case 'b': case 'B': info(); break; case 'q': case 'Q': System.out.println( "Bye."); System.exit(0); default: System.out.println( input + " is invalid.\n"); } } while (true); } public static void start() { //do something System.out.println("Press a key to return to menu"); } public static void info() { //do something System.out.println("Press a key to return to menu"); } }

12/25/1975 -> it displays:

12
25
... it hangs on the year. It think it has something to do with the delimiter (/). It doesn't have one at the end of the year so it just hangs. I don't know how you get around the problem. Any ideas?

Thanks
John

Hi,

I'm trying to break apart a string using the Scanner class, then display each string to the console. When I enter in the date 12/15/1975 it just hangs without displaying anything. Any ideas?


Scanner kbd = new Scanner(System.in); kbd.useDelimiter("/"); System.out.print("Enter date (MM/DD/YYYY): "); String month = kbd.next(); String day = kbd.next(); String year = kbd.next(); System.out.println(month); System.out.println(day); System.out.println(year);

Further problems:

I've expanded the original program to read integer values from a file. There are 20 unique values to be stored. In the file there can be multiple instances of each integer (although they will be between 5 and 24). The program should read off all values in the file. Once all values are read it will print off the value of each index and the number of times it appears in the file.

I'm having a hard time figuring out how to record the number of times a value occurs.

import java.io.*; import java.util.*; class arrays { public static void main(String[] args) throws IOException { int[] value = new int[20]; int[] frequency = new int[20]; int number = 0; String filename = "test.txt"; //create array of 20 integers: 5 - 24. for (int i = 0; i < 20; i++) { value[i] = i + 5; } BufferedReader in = new BufferedReader(new FileReader(filename)); String s = new String(); StringTokenizer st; while ((s = in.readLine()) != null) { for (int i = 0; i < 100; i++) { st = new StringTokenizer(s); number = Integer.parseInt(st.nextToken()); frequency[number]++; } } for (int i = 0; i < frequency.length; i++) { System.out.println("array [" + i + "]" + "= " + value[i]+ " occurs " + frequency[i] + " times"); } } }

I have a simple array that allows the user to enter in integer values, then prints the values of each index of the array. Is it possible to restrict each index to a different integer. In other words if the user enters in the same integer more than once it only gets stored once. Is this possible?

array[0] = 4
array[1] = 6
array[2] = 6 //doesn't get stored because it exists in [0], try again until unique
array[2] = 8
...etc for 20 unique values


import java.io.*; class TestArray { public static void main(String[] args) throws IOException { int[] array = new int[20]; BufferedReader inData = new BufferedReader(new InputStreamReader( System.in)); for (int i = 0; i < array.length; i++) { System.out.println("Enter an integer: "); array[i] = Integer.parseInt(inData.readLine()); } for (int i = 0; i < array.length; i++) { System.out.println("array [" + i + "] = " + array[i]); } } }

Jeff, Michael, thanks for the info.

Michael,

The code you posted works great for most of the invalid characters but it doesn't detect the slashes ("/" and "\"). If I enter either slash for the filename it exits out of the loop even though it's a invalid file name.

I have a loop that requires the user to enter a valid filename to continue. I currently have it set up to loop if the user hits enter without typing anything in (null). In Windows you cannot enter a filename with the forbidden characters \/:*?"<>|. Is there an easy way to check for invalid filenames or do I have to add each individual character to my validation checks (e.g. filename.equals("")||filename.equals("?")||...etc);

do{ //What is the filename? check for null value System.out.print("Please enter filename: "); filename = stdin.readLine(); if (filename.equals("")){ System.out.println("Nothing entered!"); } else{ System.out.println("\n** RECTANGLE SAVED **"); } }while (filename.equals(""));

I'm trying to read integers from a file (2 integer values separated by whitespace) that the program will use as variables. The following code works correctly. I was wondering, is there an easier method to read integer values from a file and then assign the values to specific variables?

try { BufferedReader in = new BufferedReader(new FileReader(filename)); String s = new String(); StringTokenizer st; while ((s = in.readLine()) != null) { st = new StringTokenizer(s); inWidth = Integer.parseInt(st.nextToken()); inHeight = Integer.parseInt(st.nextToken()); } in.close(); }

Thank you. It's finally starting to make sense.

Thanks for the info.

class test { static File file; public static void main(String[] args) throws IOException { BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in)); String filename=null; do{ System.out.print("Please enter filename: "); filename = stdin.readLine(); File file = new File(filename); }while (!file.exists()); } }

The problem I run into now is a Null pointer exception. If I surround the loop with a try/catch it works ok, but it only runs once. I'm not sure if I'm missing something or whether there's a problem with the logic.

I'm trying to ask the user for a file to use. If the file is found then the program continues, but if the file is not found the user is asked to enter the filename again and again until it's found. I assume I could do it with a loop, but I'm unsure of the condition to test for the file not found.

BufferedReader stdin = new BufferedReader(new InputStreamReader
System.in));
String filename = null;

do{
System.out.print("Please enter filename: ");
filename = stdin.readLine();
}while (file is not found???)

Any ideas?