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User string input validation and exception error

I'm new in Java programming and I'm trying to create a user input validation to make sure that the user only input one of the three possible strings: Mammals, Reptiles, Birds. But I'm stock on trying to validate and create a loop. So far I have this:
public void validName() {
Scanner typeInput = new Scanner(System.in);
String [] type = {"Mammals", "Reptiles", "Birds"};
System.out.println("Enter Animal Type: ");
String atype = typeInput.next();
try {
if
(!Arrays.asList(type).contains(atype)){
System.out.println("Not a correct animal");
}
}
catch(Exception e){
System.out.println(e+"Plase add the correct Animal Type: (Mammals, Reptile, or Bird");
atype= typeInput.nextLine();}
while (atype.equalsIgnoreCase("Mammals") || atype.equalsIgnoreCase("Reptile") || atype.equalsIgnoreCase("Birds"));
{ System.out.println("Continue to next step");}
}
}
When I run the previous code I get this output:
Please enter First Name
Cris
Please enter Last Name
Cruz
User logged In: Criz Cruz
Welcome to ZooOrganizer!
Enter Animal Type:
Cow
Not a correct animal
Continue to next step
------------------------------------------------------------------------
BUILD SUCCESS
-----------------------------------------------------------------------
I can't get to execute the Catch Exception neither the loop to make the user to input the animal type again.
public void validName() {
Scanner typeInput = new Scanner(System.in);
String [] type = {"Mammals", "Reptiles", "Birds"};
System.out.println("Enter Animal Type: ");
String atype = typeInput.next();
try {
if
(!Arrays.asList(type).contains(atype)){
System.out.println("Not a correct animal");
}
}
catch(Exception e){
System.out.println(e+"Plase add the correct Animal Type: (Mammals, Reptile, or Bird");
atype= typeInput.nextLine();}
while (atype.equalsIgnoreCase("Mammals") || atype.equalsIgnoreCase("Reptile") || atype.equalsIgnoreCase("Birds"));
{ System.out.println("Continue to next step");}
}
}

If you want to think about it, the prompt you have coded is actually rather cruel. It doesn't inform the User of what is expected as input. You may as well display a prompt like:
Hey, enter an Animal Type and if you guess it right
you get two free OH-Henry Bars (yum yum): -->
Be up-front with what is required from the User and if you can, make the entry as simple as possible. If you do then the errors that can be possibly produced by that User is almost completely eliminated, for example:
Enter an Animal Type (Mammals, Reptiles, Birds): -->
Now the User can see what input you're expecting. This however still has issues which your code would need to deal with and take care of such as spelling mistakes, improper letter case, no word entered, etc. In my opinion it's sort of actually a pain in the butt to have to write the word Reptile into something like a Console Application which is why I would avoid those applications, you know :
Enter the full path and file name to your Database located within
the Windows Documents folder: -->
Ya, I don't think so....next app.
When you have multiple items that can be entered then use a Menu System. This way the User can see the choices available and only needs to enter a single letter or number for the desired menu item, for example:
Select an Animal Type (1-3):
1) Mammal
2) Reptiles
3) Birds
4) Quit
Menu Choice: -->
Doing it this way also reduces the amount of code required to carry out validity. Is the entered menu choice an Integer Number, is the entry greater than or equal to 1 and is it less than or equal to 4. If not then tell the User of non-validity and loop again. Here is how you might do this with your current scheme:
String ls = System.lineSeparator();
Scanner typeInput = new Scanner(System.in);
String[] type = {"Mammals", "Reptiles", "Birds"};
String selectedAnimalType = "";
String atype = "";
// Start a prompt WHILE loop...
while (atype.equals("")) {
/* Display a Menu. Doing things this way doesn't leave
the User in the dark as to what is required for input. */
System.out.print("Select an Animal Type (1-3): " + ls
+ "1) Mammal" + ls + "2) Reptiles" + ls
+ "3) Birds" + ls + "4) Quit" + ls
+ "Menu Choice: --> ");
// Get User input...
atype = typeInput.nextLine();
// Is the Input a Valid menu choice?
if (!atype.matches("\\d") || Integer.valueOf(atype) < 1 || Integer.valueOf(atype) > 4) {
/* If it's not a string representation of a Integer numerical value OR
if it's a numerical value less than 1 OR if it's a numerical value
greater than 4 */
System.out.println("Invalid entry! Please try again..." + ls);
atype = ""; // Make atype equal null string ("") to continue WHILE loop
}
// Otherwise, was the menu choice the numerical value 4 to quit?
else if (Integer.valueOf(atype) == 4) {
// Yes, it was...
System.out.println("Quiting... Bye-Bye");
System.exit(0); // Quit (end) Application.
}
}
// Prompt loop successful...continue on with code.
/* Get the proper name for the Animal Type from the 'type' Array
based on the menu choice (numerical value minus 1) so as to get
the desired array index value. */
selectedAnimalType = type[Integer.valueOf(atype) - 1];
/* The condition for the below WHILE loop is redundant since we
would NEVER get this far unless a menu choice for either Mammal,
Reptiles, or Birds, was made, so don't bother using it. Do something
similar as to what was done in the first prompt loop above. */
while (atype.equalsIgnoreCase("Mammals") || atype.equalsIgnoreCase("Reptile") || atype.equalsIgnoreCase("Birds")) {
System.out.println("Continue to next step");
// ........................................
}

You should use a Do...While loop in this case:
public void validName() {
Scanner typeInput = new Scanner(System.in);
String [] type = {"Mammals", "Reptiles", "Birds"};
do {
System.out.println("Enter Animal Type: ");
String atype = typeInput.next();
try {
if
(!Arrays.asList(type).contains(atype)){
System.out.println("Not a correct animal");
System.out.println("Continue to next step");}
}
}
catch(Exception e){
System.out.println(e+"Plase add the correct Animal Type: (Mammals, Reptile, or Bird");
atype= typeInput.nextLine();}
} while (atype.equalsIgnoreCase("Mammals") || atype.equalsIgnoreCase("Reptile") || atype.equalsIgnoreCase("Birds"));
}

Sentinel number in if statement

For data structures and algorithms in java class I've been assigned to create a program that takes user input for an item's name and price and then averages the price. I have successfully done that, however, I am having a great deal of trouble on a certain specification for the program: a sentinel number (-1) that terminates the project. Here is my code, I will explain what the issue is after.
while(true){
System.out.print("Enter item " + (count + 1) + " name: "); // enter name
names[count] = in.next(); // next string becomes count index
System.out.print("Enter item " + (count + 1) + " price: "); // enter price
prices[count] = in.nextDouble(); // stores price entered as array index
if(prices[count] == -1) break; // if next price == -1 // the code i want to change.
if(names[count].equalsIgnoreCase("peas")) flag = true;
average += prices[count];
count++;
}
So, my issue is: I want to terminate the program when I enter -1 for the item name, not have to enter a "dummy" item name and then have to enter the sentinel number (-1).
Sorry for the long explanation, just trying to be thorough.
Thanks for taking the time to read this and help a programmer hopeful out.

You need to use a String for your comparison (but "-1" will do). Also, do it immediately after you get the input. Something like,
names[count] = in.next();
if (names[count].equals("-1")) {
break;
} // ...

Repeating error message inside a while loop [duplicate]

This question already has answers here:
Loop user input until conditions met
(3 answers)
Closed 7 years ago.
I'm currently working my way through a Udemy Java course and am practicing what i have learnt thus far.
I have the following simple program which i am planning on using to get the user to input his name.
import java.util.Scanner;
public class Adventure {
public static final int menuStars = 65;
private static Scanner input = new Scanner(System.in);
public static void main(String[] args) {
String firstName = "";
String lastName = "";
boolean validName = false;
while(!validName){
//Entering first name
System.out.println("Please enter your first name.");
try {
firstName = input.nextLine();
if(firstName.length() == 0){
throw new Exception("Please enter a first name of at least 1 character.");
}else{
//Entering last name
System.out.println("Please enter your last name.");
lastName = input.nextLine();
if(lastName.length() == 0){
throw new Exception("Please enter a last name of at least 1 character");
}else{
System.out.println("You have entered " + firstName +" " + lastName);
}
}
} catch (Exception e) {
System.out.println(e.getMessage());
continue;
}
//Used to terminate loop when both first & last names are valid
validName = true;
}
}
}
I want to make the program repeat the error message when the user inputs a blank name instead of restarting the entire program from the beginning.
E.g When the user enters a blank first name, i want the program to keep repeating "Please enter a first name of at least 1 character" and when the user enters a blank last name, for it to keep repeating "Please enter a last name of at least 1 character" until the user enters a valid name.
However, currently when the user enters a blank first name or last name, my program will repeat itself from the very beginning instead of repeating just the error message.
How would i go about making the program repeat just the error message?

Use a boolean variable that stores true when "Please enter your first name." is printed. Check before printing this string each time if this variable is false or not. Also, initialize it to false before the loop. Same idea goes for last name.
if(!printed)
{
System.out.println("Please enter your first name.");
printed=true;
}

havent tested that but i am guessing it can be like that, with out try/catch though, it just makes no sense to me using it in the way you have it on your code
String firstName = "";
String lastName = "";
System.out.println("Please enter your first name.");
firstName = input.nextLine();
while(firstName.length<1){
System.out.println("Please enter a first name of at least 1 character.");
firstName = input.nextLine();
}
lastName=input.nextLine();
while(firstName.length<1){
System.out.println("Please enter a last name of at least 1 character.");
lastName = input.nextLine();
}
System.out.println("You have entered " + firstName +" " + lastName);
Edit, some basic info about exceptions
try catch is used when something unexpected happens and you try to find a way round it. for example if an array of 10 positions is expected at some point and a smaller array (lets say 4 positions) is being used. Then this would cause an exception causing the program to terminate with no further information.
With try catch you can check what the problem is, and try to either inform the user to do something(if they can) or close the program in a better way, using System.exit() for example and saving all the work that was done till that point
An other example is that if you ask for 2 numbers to do an addition. if the user enters letters instead of number the int sum=numbA+numbB; would throw and exception. This of course could be handled using an if. but even better would be something like this

A whitespace is actually considered a character, so the check of (length == 0) doesn't work for your purposes.
Although the following code below is incomplete (ex: handles the potentially undesirable case of firstname=" foo", (see function .contains()), it does what the original post asks - when the user enters a blank first/last name, it keeps repeating "Please enter a first/last name of at least 1 character" until the user enters a valid first/last name.
import java.util.Scanner;
public class Adventure {
public static final int menuStars = 65;
private static Scanner input = new Scanner(System.in);
public static void main(String[] args) {
String firstName = "";
String lastName = "";
boolean firstNameLegal = false;
boolean lastNameLegal = false;
// Entering first name
while (!firstNameLegal) {
System.out.println("Please enter your first name.");
firstName = input.nextLine();
if (!firstName.equals(" "))
firstNameLegal = true;
else
System.out.println("Please enter a first name of at least 1 character.");
}
// Entering last name
while(!lastNameLegal){
System.out.println("Please enter your last name.");
lastName = input.nextLine();
if(!lastName.equals(" "))
lastNameLegal = true;
else
System.out.println("Please enter a last name of at least 1 character.");
}
System.out.println("You have entered " + firstName +" " + lastName);
}
}

"hasNextInt" does not detect subsequent input; where to put "nextLine"?

I am brand new at Java and this one is throwing me. Using the below code it loops through for the first question until I enter anything but an integer but after finishing that loop it does not stop for the remaining question.
Through a bit of research and reading I have found that I need to use the in.nextLine() to eat the newline character after the input. However no matter where I place the nextLine() it doesn't work? I thought it would be after the first int input = in.nextInt(); line but that did not work. Any help on where it would go and why?
System.out.print("How many CUs per course are remaining in your degree program? Enter any letter to quit: ");
while (in.hasNextInt()) { // Verify input is an integer
int input = in.nextInt();
if (input <= 0) // Verify that input is not negative or zero
{
System.out.println("Please enter a positive number or any letter to quit");
System.out.print("Add another course or any letter to quit: ");
} else {
courseCuList.add(input);
System.out.print("Add another course or any letter to quit: ");
}
}
System.out.print("How many CUs do you plan to take per term?");
while (in.hasNextInt()) {
int input = in.nextInt();
// in.nextLine(); This line consumes the \n
if (input <= 0) {
System.out.println("Please enter a whole positive number.");
System.out.println("How many CUs do you plan to take per term?");
} else {
cuPerTerm = in.nextInt();
}
}

Your problem is that in while (in.hasNextInt()) each call of hasNextInt needs to wait for user input, and then test if it is integer or not.
So each time user give integer, condition will be evaluated to ture, loop will execute and condition will need to be checked again, and if it is integer loop will execute again. This will go again and again until hasNextInt will be able to return false, for instance when user will give non-integer - like letter. But in this case condition in next loop will also return false because this non-integer value was not consumed after first loop. To let second loop work you would need to invoke nextLine two times
to consume line separator after previously put correct integer
to consume actual non-integer value
But this may also fail if user will not put any integer before non-integer value because there will be no line separator to consume.
So consider changing your logic to something similar to
boolean iterateAgain = true;
System.out.print("give me positive number: ");
while (iterateAgain) {
// this inner loop will move on only after getting integer
while (!in.hasNextInt()) {//here program waits for user input
in.nextLine();// consume non-integer values
System.out.print("that wasn't positive number, try again: ");
}
int number = in.nextInt();// now there must be number here
in.nextLine();// consume line separator
if (number > 0) {
System.out.println("you gave " + number);
// do what you want with this number
iterateAgain = false;// we can leave loop
} else
System.out.print("that wasn't positive number, try again: ");
}
If you want to execute next loop then all you need is reset iterateAgain value to true.

You need to read twice.
The exit condition on your while loop is hasNextInt() - checking to see if the next token is an integer doesn't actually clear that token, which means that the next nextLine() is going to read the token, and the subsequent nextLine() will read the newline character.
To demonstrate this, place the following between the loops:
System.out.println(in.nextLine() + " | " + in.nextLine());
For the input 4, 4, A, you will see the output:
How many CUs per course are remaining in your degree program? Enter any letter to quit: 4
Add another course or any letter to quit: 4
Add another course or any letter to quit: A
| A
How many CUs do you plan to take per term?
There are two tokens that need to be cleared from the buffer, and neither of them are integers. Because of this, no matter where you put nextLine(), it will fail - you need to insert it twice. If you only insert it once, the next token won't be an integer, and hasNextInt() will fail when the program tries to enter the second loop.
In order to get your program to work, simply insert:
in.nextLine(); in.nextLine();
before the second loop. (Note that you shouldn't put both this and the print-out in, as this will read four times.)

Scanner nextLine() issues

I've been working on a programming assignment that acts as a Scrabble dictionary for a while now. The program takes input from the user and outputs a file with a list of words, depending on what the user requests from a menu. The problem I've been having has to do with Scanner.nextLine().
I'm not aexactly sure why, but for some reason I have to press enter once sometimes before my code will take my input and store it as the variable. Essentially, I end up entering the input twice. I tried inserting Scanner.nextLine() around the code to "take up" the empty enter/spaces but it doesnt work, and I have to press enter multiple times to get it to process what I want.
Does anybody have any suggestions? I'd appreciate any and all help.
Here is a bit of the code:
System.out.println("Enter the length of the word you are" + " searching for.");
int n = -1;
while(!(n >=0)) {
if(in.hasNextInt())
n = in.nextInt();
else {
System.out.println("You have not entered a valid number.
Please enter a real number this time.");
in.nextLine();
}
}
in.nextLine();
System.out.println("Enter the first letter of the words" + " you are searching for.");
String firstLetter = "";
while(!(firstLetter.length() == 1)) {
if(in.nextLine().length() > 1) {
System.out.println("You have not entered a valid letter.
Please press enter and enter only one real letter.");
}
else if(in.hasNextInt()) {
System.out.println("Do not enter a number. Please enter one real letter.");
}
else {
in.nextLine();
firstLetter = in.nextLine();
break;
}
}
At the end of this, I have to press enter once and then input to get it to store anything in the variable firstLetter. I assume it has something to do with the nature of nextLine(), as the conditions using nextInt() give no issues.

It's because you're using both nextLine() and nextInt(), what's going on is that nextLine() is searching for a new line (enter) and nextInt will automatically stop the search if any integer is typed through System.in.
Rule of thumb: Just use Scanner.nextLine() for your input, then convert your string from Scanner.nextLine() accordingly through Integer.parseInt(string), etc.

I think you're overcompensating with too many nextLines. You may want to do that once to clear the line after the int is inputted, for example, to clear the newline, but the second time here just absorbs an extra line of input:
System.out.println("You have not entered a valid number. Please enter a real number this time.");
in.nextLine();//first time
}
}
in.nextLine();//this second time is unnecessary.
The same thing happens with your duplicate uses here:
in.nextLine();
firstLetter = in.nextLine();
break;
You should only add an extra in.nextLine() immediately between inputting nextSOMETHINGELSE() and another nextLine().
EDIT:
Additionally, note that whenever you call in.nextLine(), you are absorbing a line of input. For example, this line should be fixed:
if(in.nextLine().length() > 1){
because it reads in a line, using it up, and then checks whether that (now used-up) line is long enough.