Develop Reference

How to prevent integer input in Java?

I am trying to get my code to prevent a user input from having a number in it.
Essentially I want the code to do as follows:
ask for input
receive input
test whether or not the input contains a number(ex: 5matt vs matt)
if contains a number I want to System.out.println("Error: please do not input a number");
Heres the kicker (and why it's not a duplicate question): I can't use loops or other statements we haven't learned yet. So far the only true statements we've learned are if/else/else if statements. That means I can not use for loops, like some of the answers are suggesting. While they're great answers, and work, I'll lose points for using them.
System.out.println("Please input the first name: ");
String name1 = in.next();
System.out.println("Please input the second name: ");
String name2 = in.next();
System.out.println("Please input the third name: ");
String name3 = in.next();
name1 = name1.substring(0,1).toUpperCase() + name1.substring(1).toLowerCase();
name2 = name2.substring(0,1).toUpperCase() + name2.substring(1).toLowerCase();
name3 = name3.substring(0,1).toUpperCase() + name3.substring(1).toLowerCase();
I have this already but I can't figure out how to test if the input only contains letters.

Okay, there are many ways to deal with this. A good thing would be to use Regex (text matching stuff). But it seems that you should only use very basic comparison methods.
So, let's do something very basic and easy to understand: We iterate over every character of the input and check whether it's a digit or not.
String input = ...
// Iterate over every character
for (int i = 0; i < input.length(); i++) {
char c = s.charAt(i);
// Check whether c is a digit
if (Character.isDigit(c)) {
System.out.println("Do not use digits!");
}
}
This code is very straightforward. But it will continue checking even if a digit was found. You can prevent this using a helper-method and then returning from it:
public boolean containsDigit(String text) {
// Iterate over every character
for (int i = 0; i < input.length(); i++) {
char c = s.charAt(i);
// Check whether c is a digit
if (Character.isDigit(c)) {
return true;
}
}
// Iterated through the text, no digit found
return false;
}
And in your main program you call it this way:
String input = ...
if (containsDigit(input)) {
System.out.println("Do not use digits!");
}

Use a regular expression to filter the input
Eg
str.matches(".*\\d.*")
See this link for more info

There are several ways you could do this, among others:
Iterate over all the chars in the string and check whether any of them is a digit.
Check whether the string contains the number 1, number 2, number 3, etc.
Use a regular expression to check if the string contains a digit.
(Java Regular Expressions)

If you're allowed to define functions, you can essentially use recursion to act as a loop. Probably not what your prof is going for, but you could be just inside the requirements depending on how they're worded.
public static boolean stringHasDigit(String s) {
if (s == null) return false; //null contains no chars
else return stringHasDigit(s, 0);
}
private static boolean stringHasDigit(String s, int index) {
if (index >= s.length()) return false; //reached end of string without finding digit
else if (Character.isDigit(s.charAt(index))) return true; //Found digit
else return stringHasDigit(s, index+1);
}
Only uses if/elseif/else, Character.isDigit, and String.charAt, but recursion might be off limits as well.

How to check if there are double letters in a 4 digit code in Java

The above question might seems vague but it's actually a very simple idea which i can't seem to figure out.
It basically is a 4 digit letter code containing letters from A to F for example: ABDF, BAAF, DBAF etc.
Now I'm trying to do some post input-handling where it must become impossible to enter a letter that is already in the code cause it has to be a unique 4 digit code with no repeating letter. I've been trying to make it work but none of my code seems to work so i'm back to scratch asking you guys for help :)
I hope this is somewhat clear otherwise i'll be happy to clear it up.
Thanks in advance.

Kind of a pseudocode but it would work.
String uniquePass="";
while(uniquePass.length<4){
String userInput=getUserInputChar()
if(uniquePass.contains(userInput))
rejectInputAndNotifyUser
else
uniquePass=uniquePass+userInput
}

public static boolean hasDuplicateChars(String string) {
Set<Character> chars = new HashSet<Character>();
for (char c : string.toCharArray()) {
if (!chars.add(c)) return false;
}
return true;
}
Set is a collection that contains no duplicate elements. We will use add method which returns true if this set did not already contain the specified element.
hasDuplicateChars functions iterates over characters in the input string using toCharArray function and for loop; each character is added to the chars set which is initially empty. If add method returns false it means that we have already encountered same character before. So we return false from our function.
Otherwise input is valid and method returns true.

using this function you'll be able to see if the string contains unique characters
public static boolean checkForUnique(String str){
boolean containsUnique = false;
for(char c : str.toCharArray()){
if(str.indexOf(c) == str.lastIndexOf(c)){
containsUnique = true;
} else {
containsUnique = false;
}
}
return containsUnique;
}
Update:
This will be ran everytime a user enters a character and if it fails, this would mean there is a duplicate. You have the choice of discarding that input or showing an error.

If you're validating the complete input, you can lean on the set semantics, and a few tricks
String s = "ABAF";
int count = new HashSet<>(Arrays.asList(s.split(""))).size();
if (count - 1 == 4) {
System.out.println("All ok");
} else {
System.out.println("Repeated letters");
}
the split("") will split the string to a an array like {"","A", "B", "A", "F"}.
The new HashSet<>(Arrays.asList(s.split(""))) will create a Set with String elements, and as the Set will bounce back the elements already contained, the size of the set for e.g. "AAAF" will be 3 (it'll contain the "", "A" and "F"). This way you can use the size of the set to figure out if all letters of a String are unique
If its while typing you'll than the solution depends on the input method, but you can have something like (pseudo stuff)
if (pass.contains(letter)) {
breakAndNotifyUser();
} else {
pass+=letter;
}

How to count the number of dashes (-) in a phone number String for input validation?

What I have is a program that reads in a user-entered phone number and returns the country code (if it exists), area code (if it exists), and local 7-digit phone number.
The number must be entered as countrycode-area-local. So, the maximum number of dashed you can have in the phone number is two.
For example:
1-800-5555678 has two dashes (it has a country code and area code)
800-5555678 has one dash (it only has an area code)
5555678 has no dashes (only local number)
So, it's OK to have zero dashes, one dash, or two dashes, but no more than two.
What I am trying to figure out is how you would count the number of dashes ("-") in the string to make sure there aren't more than two instances of them. If there are, it would print an error.
So far, I have:
if(phoneNumber ///contains more more than two dashed
{
System.out.println("Error, your input has more than two dashes. Please input using the specified format.");
{
else
{
//normal operations
}
Everything works so far except for this one part. I'm not sure what method to use to do this. I tried looking at indexOf, but I am stumped.

One way do it would be to parse the number into string and then split on the dashes. If the new array you get is of length greater than 3 then give an error.
String s = "1-800-5555678";
String parts[] = s.split("-");
if (parts.length > 3) {
System.out.println("error");
} else {
// do something
}
A more memory efficient solution as suggested by samrap is:
String s = "1-800-555-5678";
int dashes = s.split("-").length - 1;
if (dashes > 2) {
System.out.print("error");
} else {
// do something
}

String phoneNumber = "1-800-5555678";
int counter = 0;
for( int i=0; i< phoneNumber.length(); i++ ) {
if( phoneNumber.charAt(i) == '-' ) {
counter++;
}
}
if(counter > 2) ///contains more more than two dashed
{
System.out.println("Error, your input has more than two dashes. Please input using the specified format.");
{
else
{
//normal operations
}

Something like this. Loop through the chars in the string and see if they are -
int nDashes = 0;
for (int i=0; i<phoneNumber.length(); i++){
if (phoneNumber.charAt(i)=='-')
nDashes++;
}
if (nDashes>2){
//do something
}

Regex and replaceAll() are your friends. Use,
int count=string.replaceAll("\\d","").length();
This will replace all the numbers with empty strings and thus all you will be left with is -s

Java - See if a string contains any characters in it

The problem i'm having is when i check to see if the string contains any characters it only looks at the first character not the whole string. For instance I would like to be able to input "123abc" and the characters are recognized so it fails. I also need the string to be 11 characters long and since my program only works with 1 character it cannot go any further.
Here is my code so far:
public static int phoneNumber(int a)
{
while (invalidinput)
{
phoneNumber[a] = myScanner.nextLine();
if (phoneNumber[a].matches("[0-9+]") && phoneNumber[a].length() == 11 )
{
System.out.println("Continue");
invalidinput = false;
}
else
{
System.out.print("Please enter a valid phone number: ");
}
}
return 0;
}
For instance why if i take away the checking to see the phoneNumber.length() it still only registers 1 character so if i enter "12345" it still fails. I can only enter "1" for the program to continue.
If someone could explain how this works to me that would be great

Your regex and if condition is wrong. Use it like this:
if ( phoneNumber[a].matches("^[0-9]{11}$") ) {
System.out.println("Continue");
invalidinput = false;
}
This will only allow phoneNumber[a] to be a 11 character long comprising only digits 0-9

The + should be outside the set, or you could specifically try to match 11 digits like this: ^[0-9]{11}$ (the ^ and $ anchor the match to the start and end of the string).

You need to put the "+" after the "]" in your regex. So, you would change it to:
phoneNumber[a].matches("[0-9]+")

Why not try using a for loop to go through each character?
Like:
public static int phoneNumber(int a)
{
while (invalidinput)
{
int x = 0;
for(int i = 0; i < phoneNumber[a].length(); i++)
{
char c = phoneNumber[a].charAt(i);
if(c.matches("[0-9+]")){
x++;
}
}
if (x == phoneNumber[a].length){
System.out.println("Continue");
invalidinput = false;
}
else
{
System.out.print("Please enter a valid phone number: ");
}
}
return 0;
}

Are the legal characters in your phone numbers 0..9 and +? If so, then you should use the regular expression [0-9+]*, which matches zero or more legal characters. (If not, you probably meant [0-9]+.) Also, you can use [0-9+]{11} instead of your explicit check for a length of 11.
The reason that your current code fails, is that String#matches() does not check whether the regular expression matches part of the string, but whether it matches all of the string. You can see this in the JavaDoc, which points you to Matcher#matches(), which "Attempts to match the entire region against the pattern."

Java - appending & passing values

I'm having trouble with passing a string and double to another class because it keeps on crashing at double cost = input.nextDouble();. Also, i was wondering if i am correct with the appending method used in public boolean addPARTDETAILS(String partDESCRIPTION, double partCOST).
For example. If the user enters the parts and cost, i want it to store that in a list and print it out with the cost appended.
Parts used:
brake pads ($50.00)
brake fluids ($25.00)
Note. Assuming that i have declared all variables and the array.
System.out.print("Enter registration number of vehicle");
String inputREGO = input.next();
boolean flag = false;
for(int i=0; i<6; i++){
if(inputREGO.equalsIgnoreCase(services[i].getregoNUMBER())){
System.out.print("Enter Part Description: ");
String parts = input.nextLine();
double cost = input.nextDouble();
services[i].addPARTDETAILS(parts, cost);
//System.out.println(services[i].getregoNUMBER());
flag = true;
}
}if(flag==false);
System.out.println("No registration number were found in the system.");
public boolean addPARTDETAILS(String partDESCRIPTION, double partCOST){
if(partDESCRIPTION == "" || partCOST <= 0){
System.out.println("Invalid input, please try again!");
return false;
}
else{
partCOST=0;
StringBuffer sb = new StringBuffer(40);
String[] parts = new String[50];
for (int i=0;i<parts.length;i++){
partDESCRIPTION = sb.append(partCOST).toString();
}
System.out.println(partDESCRIPTION);
totalPART+=partCOST;
return true;
}
}

it keeps on crashing at double cost = input.nextDouble();.
It is highly unlikely that your JVM is crashing. It is far more likely that you are getting an Exception which you are not reading carefully enough and have forgotten to include in your question.
It is far more likely your code is incorrect as you may have mis-understood how scanner works. And so when you attempt to read a double, there is not a double in the input. I suspect you want to call nextLine() after readDouble() to consume the rest of the the line.
I suggest you step through the code in your debugger to get a better understanding of what it is really doing.

Just to expand a bit on Joop Eggen's and Peter Lawrey's answers because I feel some may not understand.
nextLine doesn't play well with others:
nextDouble is likely throwing a NumberFormatException because:
next, nextInt, nextDouble, etc. won't read the following end-of-line character, so nextLine will read the rest of the line and nextDouble will read the wrong thing.
Example: (| indicates current position)
Start:
|abc
123
def
456
After nextLine:
abc
|123
def
456
After nextDouble:
abc
123|
def
456
After nextLine (which reads the rest of the line, which contains nothing):
abc
123
|def
456
Now nextDouble tries to read "def", which won't work.
If-statement issues:
if(flag==false);
or, rewritten:
if(flag==false)
;
is an if statement with an empty body. Thus the statement following will always execute. And no need to do == false, !flag means the same. What you want:
if (!flag)
System.out.println("No registration number were found in the system.");
String comparison with ==:
partDESCRIPTION == ""
should be:
partDESCRIPTION.equals("")
or better:
partDESCRIPTION.isEmpty()
because == check whether the strings actually point to the exact same object (which won't happen unless you assign the one to the other with = at some point, either directly or indirectly), not just whether the have the same text (which is what equals is for).

Data dependent error.
if(flag==false);
System.out.println("No registration number were found in the system.");
should be (because of the ;):
if (!flag) {
System.out.println("No registration number was found in the system.");
}
And
partDESCRIPTION == ""
should be:
partDESCRIPTION.isEmpty()