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()
Related
Fairly new to java and programming.
Wrote this recursive method, with the objective of asking for a valid string that is both an integer and greater than 0:
private int getDimension(String tableElement){
Integer Input= 0;
System.out.println("Define table rows "+tableElement+"'s."
+"Enter an integer >= 1:");
if( !Reader.hasNextInt() || (Input=Input.parseInt(Reader.nextLine())) <= 0)
return getDimension(tableElement);
return Input;
}
I'd like to stick to using a short and recursive method. It seems to handle the >= 0 logic fine, but blows up when i pass it something other than an integer.
Can someone explain why does that happen to me please?
hasNextInt() doesn't actually consume your input, so you're stuck with the same non-int input on your next call.
Simply spoken, your code doesn't make much (any?) sense.
First of all, there is not really a point in using a recursive method that asks the user for input; and that does not at all do anything about the argument passed to it!
private int getDimension(String tableElement){
Integer Input= 0;
Bad: you keep up mixing int and `Integer. They are not the same. And - read about java coding style guides. Variable names start lower case!
if( !Reader.hasNextInt() || (Input=Input.parseInt(Reader.nextLine())) <= 0)
The first condition gives:
true: when there is NO int ...
false: when there is an int
true leads to: calling your method again without retrieving a value from the reader.
false leads to parsing an int; and checking its value for <= 0.
In one case, you are doing a recursive call; completely ignoring the input you got from the reader; in the other case, you returning 0; or that value in input.
Solution: do something like:
while (true) {
if (reader.hasNextInt()) {
input = reader.nextInt();
break;
}
// there is no number!
read.nextLine(); // consume & throw away non-number!
print "Enter a number"
}
instead.
But seriously: start with throwing away this code.
Final side note: you do Input.parseInt() ... but that is a static method on the Integer class. Just call that as Integer.parseInt() instead! But as said; throw away your code; and learn how to properly use that Scanner class; start reading here.
Because the user can enter anything, you must always read in the line, then compare it:
String num = Reader.nextLine();
return num.matches("[1-9][0-9]*") ? Integer.parseInt(num) : getDimension(tableElement);
Here I've use regex to figure out if it's a positive number; the expression means "a 1-9 char followed by 0 or more of 0-9 chars"
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.
Why doesn't the method hasNextLine() work in Netbeans 8.1? When I press ctrl+z or ctrl+d nothing happens.Thanks
while (kb.hasNextLine()) {
String str = kb.nextLine();//reads the transaction
//isVallid checks if the transaction is valid
if (!isValid(str)) {
throw new IllegalArgumentException("The transaction is not valid");
}
int x, y;//the valuse of x and y
x = getX(str);//recognize and convert the valu of x to integer.
y = getY(str);//recognize and convert the valu of y to integer.
if (buyOrSell(str))//buyOrSell can recongnoize we buy or we sell.
{
justAddToQueueu(myQueue, x, y);// buy
} else {
capitalGain += removeAndCalculate(myQueue, x, y);// sell
}
System.out.println("Please enter the next valid transaction:"
+ "\nor press ctrl+D(ctrl+Z for mac) for exit.");
//for exit you can press ctrl+D (or
Please note that due to the OP creating a moving target question, this answer is no longer applicable.
The reason is once you call the hasNextLine, it passes that and won't go back to it. So the String str=kb.nextLine(); is now looking past that. Also, keep in mind the scope of a variable is inside the brackets it's declared in. So your 'str' isn't accessible in the rest of the program. What you'll have to do is something like this:
String check;
String str = "";
while(true){
check = kb.nextLine();
if (check.matches("^.+"))
str += check;
else
break;
}
Assuming, of course, that the purpose of your while loop was to accumulate all the user input into one String. If not, just remove the + from the +=.
Hope this helps!
I think you cound be use hasNext() rather than hasNextLine(). this is the reason :
You did not specify which version of hasNext() you meant, but basically, as long as there is another token in the data source that the scanner has encapsulated, hasNext() returns true.hasNextLine() on the other hand returns true if there is another line of input available, not just another token.
I'm very new to programming, especially Java. I need to create a program that counts how many orders each entry at a restaurant gets ordered. The restaurant carries 3 entries, hamburgers, salad, and special.
I need to set up my program so that the user inputs, say, "hamburger 3", it would keep track of the number and add it up at the end. If the user inputs "quit", the program would quit.
System.out.println("Enter the type (special, salad, or hamburger) of entrée followed by the number, or quit to exit the program.");
I'm thinking about using a while loop, setting it so if the user input != to "quit", then it would run.
What's difficult for me is I don't know how to make my program take into account the two different parts of the user input, "hamburger 3" and sum up the number part at the end.
At the end, I want it to say something like "You sold X hamburgers, Y salads, and Z specials today."
Help would be appreciated.
You'll probably want three int variables to use as a running tally of the number of orders been made:
public class Restaurant {
private int specials = 0;
private int salads = 0;
private int hamburger = 0;
You could then use a do-while loop to request information from the user...
String input = null;
do {
//...
} while ("quite".equalsIgnoreCase(input));
Now, you need some way to ask the user for input. You can use a java.util.Scanner easily enough for this. See the Scanning tutorial
Scanner scanner = new Scanner(System.in);
//...
do {
System.out.println("Enter the type (special, salad, or hamburger) of entrée followed by the number, or quit to exit the program.");
input = scanner.nextLine();
Now you have the input from the user, you need to make some decisions. You need to know if they entered valid input (an entree and an amount) as well as if they entered an available option...
// Break the input apart at the spaces...
String[] parts = input.split(" ");
// We only care if there are two parts...
if (parts.length == 2) {
// Process the parts...
} else if (parts.length == 0 || !"quite".equalsIgnoreCase(parts[0])) {
System.out.println("Your selection is invalid");
}
Okay, so we can now determine if the user input meets or first requirement or not ([text][space][text]), now we need to determine if the values are actually valid...
First, lets check the quantity...
if (parts.length == 2) {
// We user another Scanner, as this can determine if the String
// is an `int` value (or at least starts with one)
Scanner test = new Scanner(parts[1]);
if (test.hasInt()) {
int quantity = test.nextInt();
// continue processing...
} else {
System.out.println(parts[1] + " is not a valid quantity");
}
Now we want to check if the actually entered a valid entree...
if (test.hasInt()) {
int quantity = test.nextInt();
// We could use a case statement here, but for simplicity...
if ("special".equalsIgnoreCase(parts[0])) {
specials += quantity;
} else if ("salad".equalsIgnoreCase(parts[0])) {
salads += quantity;
} else if ("hamburger".equalsIgnoreCase(parts[0])) {
hamburger += quantity;
} else {
System.out.println(parts[0] + " is not a valid entree");
}
Take a look at The if-then and if-then-else Statements and The while and do-while Statements for more details.
You may also find Learning the Java Language of some help. Also, keep a copy of the JavaDocs at hand, it will make it eaiser to find references to the classes within the API
These two methods should be what you're looking for.
For splitting: String.split(String regex)
http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#split(java.lang.String)
For parsing String into an Interger: Integer.parseInt(String s)
http://docs.oracle.com/javase/7/docs/api/java/lang/Integer.html#parseInt(java.lang.String)
You can split your strings using input.split(" "). This method gives you two strings - two parts of the main string. The character you splitted with (" ") won't be found in the string anymore.
To then get an integer out of your string, you can use the static method Integer.parseInt(inputPartWithCount).
I hope this helps!
Im writing a program that calculates the investment of a person after a number of years. I prompt the users to enter their name, amount they will be investing, interest rate, and number of years. I'm supposed to do a validation of the input with if...else statements. One of the checks is to see if the user has entered the correct data type. This is for an intro java class. We finished the chapter on methods a week ago, so this is beginner's stuff. I can seem to figure out how to do the data type check. I tried the hasNextInt for my int types but I get an exception which we haven't learned at all. I found some info online on the Pattern and Match classes but there's a lot of stuff in there that we haven't seen yet. Here's one of the methods I wrote to get the correct input.
//Define method for input validation, integer type
public static int getValidInt(String messagePrompt, String messagePrompt2, String messagePrompt3){
Scanner input = new Scanner(System.in);//Create scanner
int returnValue;
int j = 0;
do {//Start validation loop
System.out.printf(messagePrompt); //Print input request
returnValue = input.nextInt();
if (returnValue <= 0) { //Check if user entered a positive number
System.out.println(messagePrompt2);//Print error message
}
else if (!input.hasNextInt()) {
System.out.println(messagePrompt3);//Print error message
}
else {
j++;
}
} while (j == 0);//End validation loop
return returnValue;
}
Im not sure if I have the order of the checks right. Any help is welcome. Thank you.
If it's just 4 pre-defined input fields and you don't have to check for additional things then I don't see a reason to use a do while loop here. Though maybe I don't get what this method is supposed to do, are you returning some kind of integer that defines whether the input was valid or do you actually have to store the values? If the former, why not just return a Boolean or an Enumeration?
I also don't understand why you're simply calling nextInt the first time, but for the next one you are checking whether it has a nextInt.
Also you don't mention what kind of exception you're getting when calling hasNextInt, but apparently this can only be an IllegalStateException. I suggest taking a look at the Java docs at http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html, or reading your relevant course material.
The sequence nextInt() and hasNextInt() is invoked. First one is used to read the value from input, and second is used to see whether the value type is int. So you have to invoke hasNext[Type]() followed by next[Type].
Let's correct those two first as below.
if (scnr.hasNextInt()) {
int userChoice = scnr.nextInt();
} else {
// input is not an int
}
Now let's correct your code to get a valid int.
public static int getValidInt(String messagePrompt, String messagePrompt2, String messagePrompt3) {
Scanner input = new Scanner(System.in);// Create scanner
int returnValue = -1;
boolean incorrectInput = true;
while (incorrectInput) {
System.out.printf(messagePrompt); // Print input request
if (input.hasNextInt()) {
returnValue = input.nextInt();
if (returnValue <= 0) { // Check if user entered a positive number
System.out.println(messagePrompt2);// Print error message
} else {
incorrectInput = false;
}
} else {
input.next();
System.out.println(messagePrompt3);// Print error message
}
}
return returnValue;
}