I am trying to use a while condition where if a user inputs a string with the first character as number 1, the loop should end. However, in my case the loop never ends. What could I be doing wrong?
public static void main(String[] args) {
ArrayList<Integer> instructions = new ArrayList<Integer>();
Scanner keyboard = new Scanner(System.in);
String input = "";
String termIns = input.substring(0);
// int termInsInt= Integer.parseInt(termIns);
do {
input = keyboard.nextLine();
int inputInt = Integer.parseInt(input);
instructions.add(inputInt);
//String termIns = input.substring(0);
} while(!termIns.equals("1"));
In addition, what would display the list of all elements in the ArrayList?
You need to update termIns with the user input in each iteration of loop:
do {
input = keyboard.nextLine();
int inputInt = Integer.parseInt(input);
instructions.add(inputInt);
termIns = input.substring(0);
} while(!termIns.equals("1"));
Also substring(0) will not help you as
substring(int beginIndex)
Returns a new string that is a substring of
this string. The substring begins with the character at the specified
index and extends to the end of this string.
You can use startsWith method instead directly on input as mentioned here
while(!input.startsWith("1"))
you're not updating termsIn which is part of your terminating condition.
Also, you can display all the elements in the Arraylist by creating a loop outside of your do-while that prints out all the elements in your arraylist. I'd take a look at the javadoc on Arraylist.
Related
I am new to Stackoverflow and this is my first time asking a question. I have searched my problem thoroughly, however, could not find an appropriate answer. I am sorry if this has been asked. Thank you in advance.
The question is from Hyperskill.com as follows:
Write a program that reads five words from the standard input and outputs each word in a new line.
First, you need to print all the words from the first line, then from the second (from the left to right).
Sample Input 1:
This Java course
is adaptive
Sample Output 1:
This
Java
course
is
adaptive
My trial to solve it
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
/* I have not initialized the "userInput" String.
* I know that String is immutable in Java and
* if I initialize it to an empty String ""
* and read a String from user.
* It will not overwrite to the "userInput" String.
* But create another String object to give it the value of the user input,
* and references the new String object to "userInput".
* I didn't want to waste memory like that.
*/
String userInput;
String[] userInputSplitFirstLine = new String[3];
String[] userInputSplitSecondLine = new String[2];
Scanner scan = new Scanner(System.in);
userInput = scan.nextLine();
userInputSplitFirstLine = userInput.split("\\s+");
userInput = scan.nextLine();
userInputSplitSecondLine = userInput.split("\\s+");
for(String firstLineSplitted: userInputSplitFirstLine) {
System.out.println(firstLineSplitted);
}
for(String secondLineSplitted: userInputSplitSecondLine) {
System.out.println(secondLineSplitted);
}
scan.close();
}
}
If you try the sample input above, the output will match the sample output above. However, if you write more than 3 words to the first line and/or more than 2 words to the second line, the userInputSplitFirstLine array of size 3 will store more than 3 words. Same goes with the userInputSplitSecondLine array also. My first question is how can an array of size 3 (userInputSplitFirstLine) and an array of size 2 (userInputSplitSecondLine) can hold more than 3 and 2 elements, respectively? My second question is that how can I restrict/limit the number of words that the user can insert in a line; for example, the first line only accepts 3 words and the second line only accepts 2 words?
Also the answer to this question suggested by Hyperskill.com is as follows:
import java.util.Scanner;
class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
String wordOne = scanner.next();
String wordTwo = scanner.next();
String wordThree = scanner.next();
String wordFour = scanner.next();
String wordFive = scanner.next();
System.out.println(wordOne);
System.out.println(wordTwo);
System.out.println(wordThree);
System.out.println(wordFour);
System.out.println(wordFive);
}
}
You can use next method of scanner object to read string and then it can be printed easily on new line.
while(true){
if(scanner.hasNext()){
System.out.println(scanner.next());
}
else{
break;
}
}
I think this should do the work. Don't hesitate to ask, if you have some questions.
import java.util.Scanner;
class App {
public static void main(String[] args) {
final StringBuffer line = new StringBuffer();
final StringBuffer words = new StringBuffer();
try (final Scanner sc = new Scanner(System.in)) {
while (sc.hasNextLine()) {
final String currentLine = sc.nextLine();
line.append(currentLine).append(System.lineSeparator());
for (final String word : currentLine.split("\\s+")) {
words.append(word).append(System.lineSeparator());
}
}
} finally {
System.out.println(line.toString());
System.out.println();
System.out.println(words.toString());
}
}
}
My first question is how can an array of size 3 (userInputSplitFirstLine) and an array of size 2 (userInputSplitSecondLine) can hold more than 3 and 2 elements, respectively?
The array here:
String[] userInputSplitFirstLine = new String[3];
is not the same one as the one you got from split:
userInputSplitFirstLine = userInput.split("\\s+");
When you do the above assignment, the old array that was in there is basically "overwritten", and now userInputSplitFirstLine refers to this new array that has a length independent of what the old array had. split always return a new array.
My second question is that how can I restrict/limit the number of words that the user can insert in a line; for example, the first line only accepts 3 words and the second line only accepts 2 words?
It really depends on what you mean by "restrict". If you just want to check if there are exactly three words, and if not, exit the program, you can do this:
userInputSplitFirstLine = userInput.split("\\s+");
if (userInputSplitFirstLine.length != 3) {
System.out.println("Please enter exactly 3 words!");
return;
}
You can do something similar with the second line.
If you want the user to be unable to type more than 3 words, then that's impossible, because this is a command line app.
By the way, the code in the suggested solution works because next() returns the next "word" (or what we generally think of as a word, anyway) by default.
hope this will help you!
public class pratice1 {
public static void main (String[]args) {
Scanner sc = new Scanner(System.in);
String input = sc.nextLine();
String input1 = sc.nextLine();
char[]a =input.toCharArray();
char[]a1 = input1.toCharArray();
System.out.println(input +""+ input1);
int a2=0;
if(input!=null) {
for(int i=0;i<input.length();i++) {
if(a[i]==' ') {
a2=i;
for(int j=0;j<a2;j++) {
System.out.println(a[i]);
a2=0;
}
}
else System.out.print(a[i]);
}System.out.println("");
for(int i=0;i<input1.length();i++) {
if(a1[i]==' ') {
a2=i;
for(int j=0;j<a2;j++) {
System.out.println(a1[i]);
a2=0;
}
}
else System.out.print(a1[i]);
}
}
}
}
To solve the problem:
Write a program that reads five words from the standard input and
outputs each word in a new line.
This was my solution:
while(scanner.hasNext()){
System.out.println(scanner.next());
}
I am required to create a method that prompts user to input three words and then it has to store the data in an array. The method should then print the three lines in reverse so for example word OVER would come out as REVO.
I have got it done sort of however I don't know how to get the other 2 lines to work. As it is, only the first user input gets reversed.
Here is the code so far;
import java.io.*;
public class Average {
public static void main (String[] args) throws IOException {
BufferedReader getit;
getit = new BufferedReader
(new InputStreamReader (System.in));
System.out.println ("Enter first line:");
System.out.flush ();
String text = getit.readLine();
while (true) {
System.out.println (reverse(text));
System.out.println("Enter 2nd line:");
System.out.flush ();
text = getit.readLine();
System.out.println("Enter 3rd line:");
System.out.flush ();
text = getit.readLine();
System.out.println("Finish");
break;
}
}
public static String reverse (String original) {
String reversed = "";
int pos = original.length() - 1;
while (pos >= 0) {
reversed = reversed + original.charAt(pos);
pos -= 1;
}
return reversed;
}
}
You called the function reverse just once. Try to call it every time you get a string.
What you are doing is, You took the first string as input and your program went into an loop near while(true) you printed the reverse of the string. You took two more strings.
Where are you reversing them? and the break at the end of the loop doesn't make sense.
you may remove the while loop and break and add call the reverse function. I am not writing any code as you could do it easily.
Write System.out.println (reverse(text)); after text = getit.readLine(); each time.
gets a single letter from the user. This method validates that it’s either a valid letter or the quit character, ‘!’. It'll eventually keep asking for characters, then once the user is done, they'll type ‘!’ to make the loop end and move on to printing their list of chars
public static String isValidLetter(){
char[] charArray;
charArray = new char[11];
charArray[0] ='C';
charArray[1] ='E';
charArray[2] ='F';
charArray[3] ='H';
charArray[4] ='I';
charArray[5] ='J';
charArray[6] ='L';
charArray[7] ='O';
charArray[8] ='P';
charArray[9] ='S';
charArray[10] ='T';
charArray[11] ='U';
String input;
char letter;
Scanner kb = new Scanner(System.in);
System.out.println("Enter a single character: ");
input=kb.nextLine();
letter = input.charAt(0);
Reading the strings from console.. type "a", enter, "b", enter, "!", enter
import java.util.*;
public class Main {
public static void main(String[] args) throws IOException {
Scanner scann = new Scanner(System.in);
List<String> letterWords = new LinkedList<String>();
String str = null;
while (!"!".equals(str)) {
str = scann.next();
letterWords.add(str);
}
for (String word : letterWords) {
System.out.println(word);
}
scann.close();
}
}
If you just want to have a "collection" of valid characters, then you also could use a String instead of an array. It would be much easier to search in it and it avoids errors like in your example (you've initialized your array with size of 11, but you're inserting 12 elements):
public static boolean isValidLetter(final char character) {
final String validCharacters = "CEFHIJLOPSTU";
return validCharacters.contains(String.valueOf(character));
}
This method expects a single char and returns true if it is valid, false otherwise. Please mind, that this check is case sensitive.
You could use that method like this:
final Scanner scan = new Scanner(System.in);
String input;
while (!(input = scan.nextLine()).equals("!")) {
if (!input.isEmpty() && isValidLetter(input.charAt(0))) {
// ... store valid input
System.out.println("valid");
}
}
This loop requests user input until he enters !. I've omitted the storing part. It is up to you to do this last part.
Modify your isValidLetter method to return boolean.
Modify your isValidLetter method to get a char as a parameter.
In isValidLetter, try to find a letter by using a helper function, something like:
static boolean contains(char c, char[] array) {
for (char x : array) {
if (x == c) {
return true;
}
}
return false;
}
Somewhere in your code where you need the input (or in main for testing), ask for user input (as you already did in isValidLetter). Perform a loop, asking for input, until it is right, or until it is your ending character.
I am not posting the complete solution code on purpose, as it is better for you to play with the code and learn. I only gave directions on how to try; of course it is not the only way, but it fits with what you've already started.
I'm supposed to input an array of strings in java according to the following specification:
Input:A text containing K English words (where K <= 5000), with spaces and punctuation marks
My approach is to use an array of strings, each string containing a word and taking input using java.util.Scanner.next() inside a loop.
My problem is how to stop taking inputs when the user hits enter. Any idea?
Use a Scanner. Read the lines that the user enters. If the user enters an empty line then exit the loop:
public static void main(String[] args) throws Exception {
final Scanner scanner = new Scanner(System.in);
while (true) {
final String read = scanner.nextLine();
if ("".equals(read)) {
break;
}
System.out.println(read);
}
}
You could use two Scanner objects to handle this like so:
Scanner inScan = new Scanner(System.in);
String line = sinScan.nextLine();
while (line.length() > 0) {
Scanner lineScan = new Scanner(line);
while(lineScan.hasNext()) {
String word = lineScan.next();
// process this word.
}
line = inScan.nextLine();
}
// loop should exit when the user enters a blank line.
I need to check the array to see if the user input is already present, and display a message as to whether it is or isn't there. The first part is working, but I tried to create a method for the word check, and I'm not sure if I'm on the right path or not, cheers.
import java.util.Scanner;
public class InputLoop {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
String array[] = new String[10];
int num = array.length, i = 0;
System.out.println("Enter a word");
for (i = 0; i < num; i++) {
while (scan.hasNextInt()) // while non-integers are present...
{
scan.next(); // ...read and discard input, then prompt again
System.out.println("Bad input. Enter a word");
}
array[i] = scan.next();
WordCheck();
}
}
public void WordCheck(String[] i) {
Scanner scan = new Scanner(System.in);
System.out.println("Enter another word");
if (scan.next().equals(array[i])) {
System.out.println("The word has been found");
} else {
System.out.println("The word has not been found");
}
}
}
Right. You've clearly gone down a bad thought process, so let's just clear the slate and have a re-think.
Step one: You want to take some user input
Step two: Compare it with all previous user inputs to see if it's present.
If it is present, return a message indicating that value has been inputted.
otherwise ignore the input and continue execution
Repeat step one.
The solution
So, let's review what you've got, and how you need to change it.
public static void main(String[] args)
If I were you, I would avoid calling methods directly from here. If you do, every method will need to be static, which is a pointless adjustment in scope for the functionality of your class. Create a new instance of your class, inside the main method, and move this code to the class' constructor. This will remove the need to make every single method static.
Scanner scan = new Scanner(System.in);
String array[] = new String[10];
Okay, so you've created a scanner object that takes input from the System.in stream. That's a reasonable thing to do when taking input from the keyboard. You've also created an array to contain each item. If you only want the user to be able to type in 10 values, then this is fine. Personally, I would use an ArrayList, because it means you can take in as many user inputs as the user desires.
Secondly, you want a function to compare the input, with all other inputs. What you have at the moment clearly isn't working, so let's have another go at it.
You will need some input, userInput, and a collection to compare it against, allInputs.
allInputs needs to be accessible from any point in the program, so it's probably wise to make it into a field, rather than a local variable.
Then, because you're comparing userInput against all values, you're going to need a foreach loop:
for(String s : allInputs)
{
if(s.equals(userInput))
{
// Output message code.
}
}
Now the trick is fitting this inside a loop that works with this program. That is up to you.
One simple solution is to use a Set:
Set<String> words = new HashSet<String>();
Add words with the add() method and check if a word is already added with contains(word) method.
EDIT
If you must use Arrays you can keep the array sorted and do a binary search:
Arrays.sort(words);
boolean isAlreadyAdded = Arrays.binarySearch(words, newWord) >= 0;
You're going to have to loop through the entire array and check if scan.next() equals any of them - if so return true - as such:
String toCheck = scan.next();
for (String string : i) { //For each String (string) in i
if (toCheck.equals(i)) {
System.out.println("The word has been found");
return;
}
}
System.out.println("The word has not been found");
This supposes you call WordCheck(), passing the array to it - this method also has to be static for you to call it from the main() method.
You can use the arraylist.contains("name") method to check if there is a duplicate user entry.