What is the way to take some parameters as optional user input using java util Scanner? Below is my code. But, for all the parameters it's blocked till the user input is entered.
I want it to continue for second parameter in cases 'when the user input is entered and then pressed enter key' "OR" 'when just pressed enter key without entering any input'.
public class MainApplication {
public static void main(String args[])
{
Scanner in = new Scanner(System.in);
System.out.println("Enter ordertypes in comma separated format (mandatory): " );
String orderOrActionTypes = in.next();
System.out.println("Enter orderAttributes (optional): " );
String orderAttributes = in.next();
System.out.println("Enter ActionAttributes (optional): " );
String actionAttributes = in.next();
}
}
You can still let the input but leave it empty.
When an input is required, the user can press Enter (which results on an empty string), and then you can test, whether the user typed something or not orderAttributes.isEmpty() and you do what you need based on the results.
Try using in.nextLine();, it may help.
Related
I have this programs and a few questions regarding to how .next(), .nextInt(), .hasNext() and .hasNextInt() of Scanner class work. Thank you in advance for any of your help :)
import java.util.Scanner;
public class test {
public static void main (String[] args) {
Scanner console = new Scanner(System.in);
int age;
System.out.print("Please enter your age: ");
while (!console.hasNextInt()) {
System.out.print("Please re-enter your age: ");
console.next();
}
age = console.nextInt();
System.out.println("Your age is "+age);
}
}
1/ When !console.hasNextInt() is executed for the first time, why does it ask for an input?
I thought at first the console is empty, so !console.hasNextInt() is True (empty is not an int), then it should go directly from "Please enter your age: " to "Please re-enter your age: " but my thought seems to be wrong.
Here, the user needs to enter something before "Please re-enter your age: " is printed.
2/ The data type of console.next() is always a String (I tried making int s = console.next(); and it gave an error), then why isn't this a infinite loop?
3/ For an instance, when it comes to console.next();, I input 21. Why does age have the value of 21? I thought because of console.hasNextInt(), I need to enter another number, and that new number will be the value of age.
The java.util.Scanner.hasNextInt() method returns true if the next
token in this scanner's input can be interpreted as an int value in
the default radix using the nextInt() method.
When you start with a non integer input, hasNextInt() will be false and you will enter while loop. Then it will prompt you to re-enter your age. But if you start with integer, you won't enter the loop. Your age will be printed.
console.next() means it takes next input token and returns String. If you write down your code as:
String s = null;
while (!console.hasNextInt()) {
s = console.next();
System.out.println("You entered an invalid input: " + s);
System.out.print("Please re-enter your age: ");
}
console.next() is being used for handling the non-integer inputs. Now, if you enter a non-integer input twenty, you'll see that console.hasNextInt() will be false and console.next() will read it.
hasNextInt() waits for an input string and then tells you if can be converted to an int. With that in mind, let's go over your questions:
When !console.hasNextInt() is executed for the first time, why does it ask for an input?
Because it blocks until there's some input from the console.
The data type of console.next() is always a String (I tried making int s = console.next(); and it gave an error), then why isn't this a infinite loop?
Because hasNextInt() returns true when the input can be converted to an int, for example "21".
For an instance, when it comes to console.next();, I input 21. Why does age have the value of 21? I thought because of console.hasNextInt(), I need to enter another number, and that new number will be the value of age.
Calling next() doesn't wait for a new input, it just swallows the input that was tested by hasNextInt() so the scanner can move on to the next one. It could have been the first statement in the loop, with the same effect.
Im having some trouble with scanning user input in one of my first java programs. When I compile and run this, I am immediately prompted for input (i.e the command line stops and blinks). When I enter anything, the first line is printed, asking me to enter an integer. Then the second line is printed and I'm prompted to enter another value.
The output from this program is the first two values that I input. This is hard to explain, but it basically asks for 3 input values and only uses two.
import java.util.Scanner;
public class objects
{
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
System.out.println("Enter an integer please...");
int input = sc.nextInt();
System.out.println("Enter your name please...");
String name = sc.nextLine();
System.out.println("The read values: " + input + ", " + name);
sc.close();
}
}
Put a System.out.flush() command after your println statements if you're reading from the console directly afterward
just use this:
Scanner sc = new Scanner(System.in);
System.out.print ("Enter your name please... ");
String name = sc.nextLine();
System.out.print ("Enter an integer please... ");
int input = sc.nextInt();
System.out.println ("The read values: " + input + ", " + name);
i just moved the integer below the name and it sorta fixed it. hahaha
When you introduce a number you press enter key, nextInt() uses the number but the enter (\n) remains buffered. After this if you call again nextInt(), Java tries to convert \n into a number giving you a NumberFormatException, but if you invoke nextLine() they read the enter as empty string
Here you have a better explanation and one solution
Can't use Scanner.nextInt() and Scanner.nextLine() together
It seems this is an error to do with my installation of VirtualBox. No matter what I try, the problem persists. Even if i try to only read ONE integer, it will ask me to input two values.
Thanks for everyone who tried to help, I learned a lot just trying to debug this.
I want to validate the user input before the program continued. For example:
A variable String name. The program displays 'Enter name' and if the user types in a number instead of a String, a message should pop up and also make the user assign a String to name.
This is what I have so far:
System.out.println("Enter name");
String name = input.nextLine();
I tried try/catch but that did not work. I tried using
if(input.hasNextInt()){System.out.println("Type in a string!");}
but that carries on through the program and still assigns a number to 'name'. It does not give the user a second chance to assign a string to 'name'
Here is something to get you started using regular expression. It only checks for a String with characters between A-Z and a-z. See what happens when you try and enter "FirstName LastName" and see if you can figure out how to fix it.
Scanner input = new Scanner(System.in);
String name;
while(true){
System.out.println("Enter name");
name = input.nextLine();
if (name.matches("[A-Za-z]+")){
break;
}else{
System.out.println("Please enter only letters");
}
}
System.out.println("Name selected: "+name);
The plus sign at the end of the brackets checks to see if you have at least one character. So if you enter a blank name, it will go to the else.
The number checking can be achived fairly simple with the String matches() method. This method tells whether or not the string matches the given regular expression.
String name = "Shrek";
if (name.matches(".*\\d+.*")) {
// Do whatever you want to do if the name contains a number
}
Try this solution that validate the input with pop up, when user inputs something invalid.
public class Test {
static String name;
public static void main(String[] args) {
final JFrame parent = new JFrame();
parent.pack();
parent.setVisible(false);
name = JOptionPane.showInputDialog(parent,
"Enter name", null);
while (true) {
if (name.matches("[A-Za-z]+")) {
break;
} else {
name = JOptionPane.showInputDialog(parent,
"Please enter only letters", null);
if (name.matches("[A-Za-z]+"))
break;
}
}
System.out.println("Name selected: " + name);
}
}
I am trying to create a program that asks a user for a sentinel value (a value to enter when they want to end the list). It then asks the user to enter numbers until they re-enter the sentinel value. It then figures out the max number in the list. I'm very new to Java, and whenever I run the program is just asks for the sentinel value then does nothing else (never pops up the second input dialog). I'm sure it's something simple that I'm doing wrong, but I can't figure it out. Thanks for any help.
import java.util.*;
import javax.swing.JOptionPane;
public class HW1 {
/**
* #param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner input = new Scanner(System.in);
int number;
int max;
int sentinel;
int count=0;
JOptionPane.showInputDialog("Please enter a sentinel value: ");
sentinel=input.nextInt();
JOptionPane.showInputDialog("Please enter numbers. Enter" + sentinel +" to end.");
number = input.nextInt();
max = number;
while (number!=sentinel){
count +=1;
if (number>max)
max=number;
JOptionPane.showInputDialog("Please enter numbers. Enter" + sentinel +" to end.");
number = input.nextInt();
}
if (count!=0){
JOptionPane.showMessageDialog(null, "The max is:" + max);
}
}
}
You are mixing the ways to input data to your program. Let's begin:
Scanner input = new Scanner(System.in);
The line above allows you to catch data in the command line from the keyboard.
JOptionPane.showInputDialog("Please enter a sentinel value: ");
This Option Pane is showing correctly, you put a value and then nothing happens. This is because your program is waiting to input something in the command line
sentinel=input.nextInt();
When your program arrives to the line above, the input.nextInt() stops the program until you put something in the command line.
The correct way should be something like this:
sentinel = Integer.parseInt(JOptionPane.showInputDialog("Please enter a sentinel value: "));
number = Integer.parseInt(JOptionPane.showInputDialog("Please enter numbers. Enter" + sentinel +" value to end."));
And remove:
number = input.nextInt();
sentinel=input.nextInt();
I think the confusion is this:
the JOptionPane opens with an input dialog
when the option pane closes, whatever you put there is ignored
then the code goes to this line sentinel=input.nextInt();
which waits for input from the console (e.g. you need to go back to the console, type the number there and press enter, only then the program will advance, it will block untill you do)
I would change it to something like this:
String sentinelInput = JOptionPane.showInputDialog("Please enter a sentinel value: ");
sentinel= Integer.parseInt(sentinelInput);
(repeat for all places where you expect input)
An alternative solution is
Don't use the JOptionPane, and instead just System.out.println to print the user a request for input (instead of the popup dialog). Then you can and keep the existing input.nextInt() calls to collect it.
Just note that all interaction will be in the console, without any popup dialogs (which I actually prefer in terms of user experience, and also it will be working in non GUI machines such as a linux terminal...)
I need help doing the following:
receiving input using Scanner class (I got this)
taking input from scanner and making it a String
use replaceAll to remove numbers 0-9 from user input.
The below code is what I have so far but it is only returning user input and not removing numbers:
public static void main(String[] args) {
Scanner firstname = new Scanner(System.in);
System.out.println("Please enter your first name:");
String firstname1 = firstname.next();
firstname1.replaceAll("[^0-9]","");
System.out.println(firstname1);
Updated Code. Thank you Hovercraft. I am now investigating how to retrieve all alpha characters as with the code below, I am only getting back the letters prior to the numeric values entered by the user:
import java.util.Scanner;
public class Assignment2_A {
public static void main(String[] args) {
Scanner firstname = new Scanner(System.in);
System.out.println("Please enter your first name:");
String firstname1 = firstname.next();
firstname1 = firstname1.replaceAll("[^A-Z]","");
System.out.println(firstname1);
String input = yourScannerObject.nextLine ();
where "yourScannerObject" is the name you give your scanner.
What method did you use to scan? is it {scanner object name}.next() ?
if so you have got a string and all that you have to do is create some string, and save the input to it, e.g.:
String str="";
str = {scanner object name}.next();
before using anything in java, I would advise you to read the API :
http://docs.oracle.com/javase/1.5.0/docs/api/java/util/Scanner.html#next()
receiving input using Scanner class (I got this)
taking input from scanner and making it a String
use replaceAll to remove numbers 0-9 from user input.
Here's an example:
String in;
Scanner scan = new Scanner("4r1e235153a6d 6321414t435hi4s 4524str43i5n5g");
System.out.println(in = (scan.nextLine().replaceAll("[0-9]", ""))); // use .next() for space or tab
Output:
read this string
The problem in your code is the regex "[^A-Z]" is set to remove all non-alphabet capital characters. This means you remove all lower case as well. You could say "[^a-zA-Z]", but then you're also removing special characters.