public int cut(int b){
String str1;
b = 0;
Scanner str = new Scanner(System.in);
System.out.println("Write your string: ");
str1 = str.next();
Scanner in = new Scanner (System.in);
System.out.println("Write a number: ");
int num1 = in.nextInt();
System.out.println("Write another number: ");
int num2 = in.nextInt();
System.out.println(str1.substring(num1, num2));
return b;
}
This is my code so far. I want for a user to write a string and write from where to where he wants to cut the string he just entered. The part I can't get is getting that substring.
If you're having spaces in your string. Use Scanner#nextLine() instead.
For an input, "my input string"
str1 = str.next(); // returns "my" only
because space is Scanner's default delimiter. To read the whole line use
str1 = str.nextLine(); // returns "my input string"
Secondly, you're not using Scanner str to read the numbers at all. It should be
int num1 = str.nextInt(); // instead of in.nextInt()
You should also check that the numbers are within bounds or, I think better catch IndexOutOfBoundsException itself. Would take care of negatives and what not.
try {
System.out.println(str1.substring(num1, num2));
} catch (IndexOutOfBoundsException e) {
System.out.println("Range specified is out of bounds for '" + str1 + "'");
}
Related
I am trying to validate a user's input and check if the inputted number is an integer. Id like to throw them an error message if the number isn't an integer. I am getting stuck on the line Integer.parseInt(number); Any suggestions would be very appreciated.
import java.util.Scanner;
public class Sums {
public static int number;
public static void main(String[] args) {
int evenSum, oddSum = 0;
int posInt;
Scanner input = new Scanner(System.in);
System.out.println("Enter a postitive integer: ");
int number = input.nextInt();
try {
Integer.parseInt(number);
System.out.println("Value entered is " + number);
} catch (NumberFormatException e) {
System.out.println(number + " is not an integer.");
}
}
}
I have changed the int number = input.nextInt(); to String number = input.next(); and it works.
The issue here is that when you call Integer.parseInt(number) you are trying to parse the variable number which is an int and not a String. This means that you are doing the error checking on a conversion from an int to an Integer and not a String to an Integer.
To fix this, input a string instead of a number, then perform the conversion on the string, not the number.
...
public static void main(String[] args) {
int myNumber;
Scanner input = new Scanner(System.in);
System.out.println("Enter a postitive integer: ");
String numberString = input.nextLine();
try {
myNumber = Integer.parseInt(number);
System.out.println("Value entered is " + myNumber);
// do what you want with the number
} catch (NumberFormatException e) {
System.out.println(numberString + " is not an integer.");
}
}
...
You don't need explicitly to convert your number to an integer, Scanner.nextInt() already does that for you, i.e. Scanner.nextInt() scans the next token of the input as an int. So just remove the line "int number = input.nextInt();" from your code. In general, Integer.parseInt() is preferable when you want to convert a String representation of an Integer value as a signed decimal integer. For instance, if you would have used Scanner.nextLine() instead of Scanner.nextInt(), then it makes more sense to convert it to a signed decimal integer if you want to perform subsequent operations using that integer value.
int number = input.nextInt();
The variable number is already an int, that is why you can not hand it over to the method. The method requires a String.
If you want to use the method like you did, you should use
input.next()
as argument because it returns the input as String and initialize number within the try block, e.g.
public static void main(String[] args) {
int evenSum, oddSum = 0;
int posInt;
System.out.println("Enter a postitive integer: ");
Scanner input = new Scanner(System.in);
try {
number = Integer.parseInt(input.next());
System.out.println("Value entered is " + number);
} catch (NumberFormatException e) {
System.out.println("Not an integer.");
}
}
Bug here is int number = input.nextInt();
When you want to convert a String to a primitive datatype we use class.parseXXX(String)
You see I have written String in the function .parseXXX(String) Cause it takes String as a parameter and nothing else
So lets read your code
Integer.parseInt(number);
Here its .parseXXX(int) and clearly its not matching .parseXXX(String)
So in order to give String as parameter, you have accept String as input from user.
Replace this int number = input.nextInt(); with String number = input.next();
So now below code is valid cause its in .parseXXX(String)
Integer.parseInt(number);
Changed code:
int evenSum, oddSum = 0;
int posInt;
Scanner input = new Scanner(System.in);
System.out.println("Enter a postitive integer: ");
String number = input.next(); // <-- Changed
try {
Integer.parseInt(number);
System.out.println("Value entered is " + number);
} catch (NumberFormatException e) {
System.out.println(number + " is not an integer.");
}
New to java. I need to ask the user the number of strings (consisting only of upper and lowercase letters, spaces, and numbers) they want to input. These strings need to be stored in an array. Then I created a boolean method to be able to tell if those strings are palindromic (ignoring spaces and cases). If it is palindromic then I add to the result list to print later on. I am confused on how to ask the user to input that exact amount of strings and how to check each individual string. I must use StringBuilder. This is what I have so far (it's kind of a mess, sorry). I feel like I'm using the StringBuilder/array wrong, how can I fix this?
public class Palindromes {
public static void main(String[] args) {
int numOfStrings;
Scanner scan = new Scanner(System.in); // Creating Scanner object
System.out.print("Enter the number of strings: ");
numOfStrings = scan.nextInt();
System.out.print("Enter the strings: ");
StringBuilder paliString = new StringBuilder(numOfStrings);
for(int n=0; n < paliString; n++){
paliString[n] = scan.nextLine();
scan.nextLine();
String[] stringPali = new String[numOfStrings];
StringBuilder str = paliString;
if(isPali(userString)){
paliString = append.userString;
}
System.out.println("The palindromes are: " + userString ";");
}
static boolean isPali(String userString) {
int l = 0;
int h = userString.length() - 1;
// Lowercase string
userString = userString.toLowerCase();
// Compares character until they are equal
while (l <= h) {
char getAtl = userString.charAt(l);
char getAth = userString.charAt(h);
// If there is another symbol in left
// of sentence
if (!(getAtl >= 'a' && getAtl <= 'z'))
l++;
// If there is another symbol in right
// of sentence
else if (!(getAth >= 'a' && getAth <= 'z'))
h--;
// If characters are equal
else if (getAtl == getAth) {
l++;
h--;
}
// If characters are not equal then
// sentence is not palindrome
else
return false;
}
// Returns true if sentence is palindrome
return true;
}
}
SAMPLE RESULT:
Enter the number of strings: 8
Enter the strings:
Race Car
Mountain Dew
BATMAN
Taco Cat
Stressed Desserts
Is Mayonnaise an instrument
swap paws
A Toyotas a Toyota
The palindromes are: Race Car; Taco Cat; Stressed Desserts; swap paws; A Toyotas a Toyota
As I think the best way to answer this is to help you learn in small steps, I tried to stick with your initial idea on how to solve this and edited your main method with minimal changes.
This one does the trick.
public static void main(String[] args) {
int numOfStrings;
Scanner scan = new Scanner(System.in); // Creating Scanner object
System.out.print("Enter the number of strings: ");
numOfStrings = scan.nextInt();
scan.nextLine(); // you need this to catch the enter after the integer you entered
System.out.print("Enter the strings: ");
StringBuilder paliString = new StringBuilder();
for (int n = 0; n < numOfStrings; n++) {
String userString = scan.nextLine();
if (isPali(userString)) {
if (paliString.length() > 0) {
paliString.append("; ");
}
paliString.append(userString);
}
}
System.out.println("The palindromes are: " + paliString);
}
Key changes:
I added scan.nextLine(); right after reading the number of strings. This handles the newline you get when the user hits enter.
You don't need to initialize the StringBuilder with numOfStrings. This just preallocates the size of the StringBuilder in characters. Not the number of strings. Either way, it's not necessary. StringBuilder grows as needed.
I suggest you inspect what I did inside the for-loop. This was the biggest mess and changed significantly.
Last but not least: Writing the result needs to be outside of the for-loop, after all palindromes have been added to the StringBuilder.
Edit
Based on your comment, in this next iteration, I changed the usage of StringBuilder to the usage of an ArrayList. (Which is something completely different)
I am using it here because Lists in Java grow on demand. And since the number of palindromes is probably not equal to the number of input strings, this is the way to go. To really assign it to an array, one could always call String[] paliStringsArray = paliStrings.toArray(new String[]{}); but as ArrayLists already use an underlying array and are not necessary to to generate the output you want, I didn't put it into the new version.
Please compare the differences of this step to the previous version. I also added this String.join("; ", paliStrings) part, which creates the output you want.
public static void main(String[] args) {
int numOfStrings;
Scanner scan = new Scanner(System.in); // Creating Scanner object
System.out.print("Enter the number of strings: ");
numOfStrings = scan.nextInt();
scan.nextLine(); // you need this to catch the enter after the integer you entered
System.out.print("Enter the strings: ");
List<String> paliStrings = new ArrayList<>();
for (int n = 0; n < numOfStrings; n++) {
String userString = scan.nextLine();
if (isPali(userString)) {
paliStrings.add(userString);
}
}
System.out.println("The palindromes are: " + String.join("; ", paliStrings));
}
And now to the last step. Arvind Kumar Avinash actually solved a part that I also missed in the initial question. (I'll read more carefully in the future). He was validating the user input. So for the last iteration, I added his validation code in a modified way. I put it into a method as I think that makes things clearer and gets rid of the necessity of a the boolean valid variable.
public static void main(String[] args) {
int numOfStrings;
Scanner scan = new Scanner(System.in); // Creating Scanner object
System.out.print("Enter the number of strings: ");
numOfStrings = scan.nextInt();
scan.nextLine(); // you need this to catch the enter after the integer you entered
System.out.print("Enter the strings: ");
List<String> paliStrings = new ArrayList<>();
for (int n = 0; n < numOfStrings; n++) {
String userString = readNextLine(scan);
if (isPali(userString)) {
paliStrings.add(userString);
}
}
System.out.println("The palindromes are: " + String.join("; ", paliStrings));
}
static String readNextLine(Scanner scanner) {
while (true) {
String userString = scanner.nextLine();
if (userString.matches("[A-Za-z0-9 ]+")) {
return userString;
} else {
System.out.println("Error: invalid input.");
}
}
}
I need to ask the user the number of strings (consisting only of upper
and lowercase letters, spaces, and numbers) they want to input. These
strings need to be stored in an array.
I have done the above part of your question. I hope, this will give you direction to move forward.
import java.util.Scanner;
public class Main {
public static void main(String args[]) {
Scanner scan = new Scanner(System.in);
boolean valid = true;
int numOfStrings = 0;
do {
valid = true;
System.out.print("Enter the number of strings: ");
try {
numOfStrings = Integer.parseInt(scan.nextLine());
} catch (NumberFormatException e) {
System.out.println("Error: invalid input.");
valid = false;
}
} while (!valid);
String[] stringPali = new String[numOfStrings];
String input;
for (int i = 0; i < numOfStrings; i++) {
do {
valid = true;
System.out.print("Enter a string consisting of only letters and digits: ");
input = scan.nextLine();
if (!input.matches("[A-Za-z0-9 ]+")) {
System.out.println("Error: invalid input.");
valid = false;
}
} while (!valid);
stringPali[i] = input;
}
}
}
A sample run:
Enter the number of strings: a
Error: invalid input.
Enter the number of strings: 3
Enter a string consisting of only letters and digits: Arvind
Enter a string consisting of only letters and digits: Kumar Avinash
Enter a string consisting of only letters and digits: !#£$%^&*()_+
Error: invalid input.
Enter a string consisting of only letters and digits: Hello #
Error: invalid input.
Enter a string consisting of only letters and digits: Hello 123
Feel free to comment in case of any doubt/issue.
Wish you all the best!
[Update]
Based on your request, I have posted the following update which asks for the strings only once and then allows the user to enter all the strings one-by-one:
import java.util.Scanner;
public class Main {
public static void main(String args[]) {
Scanner scan = new Scanner(System.in);
boolean valid = true;
int numOfStrings = 0;
do {
valid = true;
System.out.print("Enter the number of strings: ");
try {
numOfStrings = Integer.parseInt(scan.nextLine());
} catch (NumberFormatException e) {
System.out.println("Error: invalid input.");
valid = false;
}
} while (!valid);
String[] stringPali = new String[numOfStrings];
String input;
System.out.println("Enter " + numOfStrings + " strings consisting of only letters and digits: ");
for (int i = 0; i < numOfStrings; i++) {
do {
valid = true;
input = scan.nextLine();
if (!input.matches("[A-Za-z0-9 ]+")) {
System.out.println("Error: invalid input.");
valid = false;
}
} while (!valid);
stringPali[i] = input;
}
}
}
A sample run:
Enter the number of strings: 3
Enter 3 strings consisting of only letters and digits:
Arvind
Kumar
He$ll0
Error: invalid input.
Avinash
Feel free to comment in case of any doubt.
This question already has answers here:
How do I ensure that Scanner hasNextInt() asks for new input?
(2 answers)
Closed 6 years ago.
Desired outcome:
Accepts user input
Makes sure user inputs only 1 integer value at a time
Stores that integer in a variable
I tried to achieve this by doing the following:
Store user input in variable
Count number of tokens in variable
If there's not one token, reject the input
If the input is not of data type int, reject the input
Code:
Scanner scan = new Scanner(System.in);
System.out.println("Enter an integer:");
String myString = scan.nextLine();
int tokens = new StringTokenizer(myString, " ").countTokens();
while (tokens != 1 && !scan.hasNextInt()) {
System.out.println("Enter a single integer");
myString = scanner.nextLine();
tokens = new StringTokenizer(myString, " ").countTokens();
}
int number = scanner.nextInt();
System.out.println(number);
This code is full of holes. The output is inconsistent and undesired. It typically ends by throwing a java.util.InputMismatchException error, indicating the value it's trying to store isn't an int. I've experienced this error occur after one loop and after multiple loops, even with the same type and quantity of input (e.g. 2 strings).
Should I keep going with this code, or should I try to approach this problem from a different angle?
I've modified your program a little bit. My approach was to accept a single line of input. If the input contains more than one token, ask the user to re-enter input. If there is only one input, check if the input is an integer, if not, as the user to again provide input.
Seems to work for me:
Scanner scanner = new Scanner(System.in);
String myString;
int tokens;
int number;
do {
System.out.println("Enter a single integer");
myString = scanner.nextLine();
tokens = new StringTokenizer(myString, " ").countTokens();
try {
number = Integer.parseInt(myString);
} catch(NumberFormatException e) {
tokens = 0;
number = -1;
}
}while (tokens != 1);
scanner.close();
System.out.println(number);
Update: Alternate approach without using StringTokenizer
Scanner scanner = new Scanner(System.in);
String myString;
boolean validInput;
int number;
do {
System.out.println("Enter a single integer");
myString = scanner.nextLine();
try {
number = Integer.parseInt(myString);
validInput = true;
} catch(NumberFormatException e) {
validInput = false;
number = -1;
}
}while (validInput == false);
scanner.close();
System.out.println(number);
Update 2: Another approach using regular expressions to validate input before accepting it.
The Scanner allows us to use a regular expression to match the input. If the input matches the pattern, you can use it to accept the input. Otherwise, discard it and ask user to provide input again.
Here's the code:
Scanner scanner = new Scanner(System.in);
System.out.println("Enter a single integer");
String integerPattern = "[+-]?\\d+$"; // positive or negative and digits only
while(scanner.hasNext(integerPattern) == false) {
String x = scanner.nextLine();// capture and discard input.
System.out.println("Enter a single integer. '" + x + "' is an invalid input.");
}
int number = scanner.nextInt(); // capture input only if it matches pattern.
scanner.close();
System.out.println("number: " + number);
Hope this helps!
Below code outputs only "Enter a string" and accepts user input however, does not display the number of characters in the string. Kindly help!
System.out.println("Enter a string");
Scanner scan = new Scanner(System.in);
String result = scan.nextLine();
try {
while (a != null) {
count++;
}
} catch (Exception e) {
System.out.println("Invalid string");
}
System.out.println("The number of characters are : " + count);
You can use String.length() to calculate the length of your input string:
System.out.println("Enter a string");
Scanner scan = new Scanner (System.in);
String a = scan.nextLine();
System.out.println("The number of characters are : " + a.length());
oschlueter is right. Also, when using java.util.Scanner to get a string from user input, you won't need a try/catch to look for invalid strings, as anything the user can input can be a String. However, you will need a Try/Catch when asking for a number through Scanner.nextInt.
Also, it's generally recommended to catch a specific error and not just Exception. In this case, you would catch java.util.InputMismatchException.
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int inputInt = checkInput(in, "Enter an integer and a base: ");
int inputBase = checkInput(in, "");
}
public static int checkInput(Scanner in, String prompt) {
System.out.print(prompt);
while (!in.hasNextInt()) {
in.next();
System.out.println("Sorry, that is an invalid input.");
System.out.print(prompt);
}
return in.nextInt();
}
This method works and doesn't return any bad input i.e., ; p "hello".
My question is how can I limit the number of inputs the scanner will read. Say I input 5 five % ; but I only want 5 and five to be passed in to my method and the rest dropped.
I looked through the Java API but couldn't find a method that would limit the amount of user input accepted. Am I just missing it or is there another way to do this?
Edit: I have tried using the .length() method to limit the input but then that doesn't allow integers greater than the .length() parameter.
Here is a working sample of how you could accomplish what you need. I broke it up so that the user is prompted once for each input which makes it easier to validate. I changed your checkInput method to getInput which only returns valid user input as a String where it is then converted into an int.
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int inputInt = Integer.parseInt(getInput(in, "Enter an integer: "));
int inputBase = Integer.parseInt(getInput(in, "Enter a base: "));
System.out.println("Int: " + inputInt + ", base: " + inputBase);
}
public static String getInput(Scanner in, String prompt) { // Get valid user input
System.out.print(prompt); // Tell user what to input
String text = "";
while (true) { // Keep looping until valid input is found
text = in.nextLine(); // Get input from stdin
if(isInteger(text)) // Check if they put in integer
break; // Exit loop
System.out.print("Try again, " + prompt); // Wasn't valid, prompt again
}
return text; // Return valid user input
}
private static boolean isInteger(String str) { // Check if string is integer
try {
Integer.parseInt(str); // If this doesn't fail then it's integer
return true;
} catch(NumberFormatException e) {
return false; // Wasn't integer
}
}
Sample run:
Enter an integer: 2 dog five 3
Try again, Enter an integer: 2
Enter a base: cat
Try again, Enter a base: 3
Int: 2, base: 3
It helps to separate functionality - you were trying to read input, validate input, and convert to int all in one method. If you break it up it becomes easier to manage.
Scanner sc= new Scanner(System.in);
String string = sc.findInLine(".{500}"); // length of your input you want
findInLine(String pattern)
method of Scanner class of java.util package. This method returns a String object that satisfies the pattern specified as method argument.
see this article
If you want to only get the first two words (or strings delimited by spaces) you can use the str.split(" "); method.
For example:
String input = in.nextLine(); // Gets the next line the user enters (as a String)
String[] inputWords = input.split(" "); // inputWords[0] is first word, inputWords[1]
// is second word... etc
String validInput = inputWords[0] + " " + inputWords[1]; // Combines the first and
// second words into a string, so if you had "5 five %" validInput would be "5 five"
// inputWords[0] is "5", inputWords[1] is "five", inputWords[3] is "%" etc for any other words...
This will essentially limit the number of inputs to two words. I hope this helps!
Scanner scan = new Scanner(System.in);
System.out.println ("enter a 2 numbers");
String s;
s = scan.nextLine();
Scanner scan2 = new Scanner(s);
int one = scan2.nextInt();
int two = scan2.nextInt();
System.out.println (" int 1 = " + one + " int 2 = " + two);
enter a 2 numbers
23 45 68 96 45
int 1 = 23 int 2 = 45
Process completed.