Program overview: Ask user for phrase, ask user for an index in which a scramble will rotate the phrase until that letter at index is the first index (0) of the string. Ask for an Integer until an integer is given. After phrase is scrambled ask to scramble again. if yes, scramble to inputted index, if no, print final result end program.
Code:
import java.util.Scanner;
public class PJ {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
String phrase;
String phraseMut;
int index = 0;
System.out.println("Enter your word or phrase: ");
phrase = scan.nextLine();
phraseMut = phrase;
System.out.println();
while (true) {
System.out.println("Enter an Integer: ");
if (scan.hasNextInt()) {
index = scan.nextInt();
scan.nextLine();
break;
} else if (index > phraseMut.length()) {
System.out.println("Error: Index is out of bounds.");
System.out.println("Please enter an integer value.");
} else {
System.out.println("Error: Index is not Integer.");
}
}
System.out.println();
System.out.println("Rotating phrase to bring index "+index+" to the front. . .");
int count =0;
for(int i = 0; i < index; i++){
phraseMut = phraseMut.substring(1,phrase.length())+""+phraseMut.substring(0,1);
count++;
System.out.println(phraseMut);
}
}
}
Issue: The while loop is running infinitely but what I need it to do is to check if its an integer, if it is, leave the loop and continue. If it's not an integer, keep asking for input until its an integer and same with if the integer is in the index range.
Scanner isn't actually designed for keyboard input, but you can use it for that. When you invoke hasNextInt(), and the next token is, say, "hello", then hasNextInt() does exactly what it says in its javadoc: It concludes the next token is not an int, and tells you so. That is it. It does not consume that "hello", so, if hasNextInt() returns false once, it will do so forever, at least, until you 'consume' the token.
Secondarily, you are expecting keyboard input to be separated out by single enter presses, but scanner isn't configured properly out of the box for that. You're badly hacking around it by invoking scan.nextLine() from time to time. This is bad; it means if the user ever touches the space bar (you know, the biggest key on the keyboard), all hell breaks loose as you're now out of sync on those nextlines, and it is also impossible to read blank input.
The fix for that is to tell the scanner you're using it for keyboard input - that you expect entries to be separated by enter keys. To do so, immediately after making the scanner, invoke .useDelimiter("\\R") (That's: A newline symbol, in regexp-ese). Then, never invoke .nextLine() - to read an entire line, invoke .next(). All inputs are entire lines (you hit 'enter' after entering a number just the same).
Thus:
Call .useDelimiter("\\R")
Delete all nextLine() calls you interject.
If you want an actual line, use .next(), not nextLine()
Consume the token if hasNextInt() returns false, by invoking .next() and ignoring its return value.
Related
I keep trying to get this to work but when I enter in the numbers and enter them into the console it does not finish. I have to terminate myself.
import java.util.Scanner;
public static void main(String[] args) {
int cmlSum = 0;
int inputNum;
String outputSum = "";
Scanner keyboard = new Scanner(System.in);
System.out.println("Enter sequence of numbers ");
do {
inputNum = keyboard.nextInt();
cmlSum += inputNum;
outputSum += String.format("%s ", String.valueOf(cmlSum));
} while (keyboard.hasNextInt());
System.out.println(outputSum);
}
Well, yes. The keyboard.hasNextInt() call will return false for two reasons.
The next token is a NOT an integer.
You have reached the end-of-input.
What is (most likely) happening is that you have stopped entering numbers. The program is (patiently) waiting for you to enter ... something.
Solutions:
Tell the user to enter the (OS specific) terminal "end of file" character. On Linux it is CTRL-D. On Windows CTRL-Z.
Tell the user to enter something that isn't an integer.
Pick an integer as meaning that there are no more numbers, and test for that.
You also need to instruct the user how to "end" the sequence; e.g.
System.out.println("Enter sequence of numbers. Enter a non-number to stop.");
This is actually a problem with your application's "user interface" design. If the user is expected to type an arbitrarily long sequence of numbers (or something else), then there needs to be some way for the user to tell the program that the sequence is finished. The program cannot magically distinguish the cases of "there are no more" and "hang on, I'm taking a break from typing".
The hasNext() method checks if the Scanner has another token in its input. A Scanner breaks its input into tokens using a delimiter pattern, which matches whitespace by default. That is, hasNext() checks the input and returns true if it has another non-whitespace character.
In this case hasNext() won't return true because there is neither any integer nor any whitespace. Therefore the program waits for the next input. Besides use a specific integer to break the loop.
for instance,
System.out.println("Input -1 will end the program!";
do{
int x = keyboard.nextInt();
if(x == -1){
break;
}
//do something
}while(true);
Your code is ok. There is no issue.
But before writing code, we need to think about it. The workflow of your code below:
1st time when we enter do loop, keyboard.nextInt() takes input from us.
Then it calculates the sum and performs string operation.
After that, while's keyboard.hasNextInt() takes next input from you.
Checks your input. If your input is not an integer, while loop will terminate(break).
If your input is an integer then, code loop back to keyboard.nextInt(). But this time, it does not take input from you.
It pases the buffered input(keyboard.hasNextInt()) to keyboard.nextInt() and assign the value to inputNum
So, when you want to terminate while loop, you should input any character like a, b, c, etc.
You haven't specified when the loop will end. Have a condition such as inputting a certain number that will end the program once entered, as currently your program is just going to wait for more input. Something like :
System.out.println("Enter sequence of numbers to add. Enter '0' to end the program");
do {
inputNum = keyboard.nextInt();
cmlSum += inputNum;
outputSum += String.format("%s ", String.valueOf(cmlSum));
} while (inputNum != 0);//Keeps going as long as 0 is not entered
//When zero is entered, program shows the total sum and terminates
if (inputNum == 0) {
System.out.println("The sum of all total numbers: ");
System.out.println(outputSum);
System.exit(0);//Terminates program
}
Basic syntax of do-while Loop:
do{
// do something
}while(terminating condition);
If you are using hasNextInt() method of Scanner object for terminating condition in do-while loop then loop will be terminated once it get input other than an integer value (e.g float, double, char, String etc.. ) as shown in below complete program.
import java.util.Scanner;
public class Cumulative{
public static void main(String[] args){
int cmlSum = 0;
int inputNum;
String outputSum = "";
Scanner keyboard = new Scanner(System.in);
System.out.println("Enter sequence of numbers ");
do{
inputNum = keyboard.nextInt();
cmlSum += inputNum;
outputSum += String.format("%s ", String.valueOf(cmlSum));
}while (keyboard.hasNextInt()); // loop will terminated whenever get any value other than valid integer such as float char or String etc..
System.out.println(outputSum);
}
}
I'm trying to put user input into an array but the hasNextInt() method will not return false and stop the input.
public static void main (String[] args) {
Scanner in = new Scanner(System.in);
int target = in.nextInt();
while(in.hasNextInt()) {
weights.insert(in.nextInt());
}
recKnapSack(target, 0);
}
Scanner.hasNextInt() will return false when it encounters a non-integer character in its buffer.
However, it may strip out whitespace when it's reading prompts. So Space+Enter or Enter will most likely not stop the loop. But any other character will.
Since you'd like to input any number of ints, you must instruct the user on what to type when they're done. In fact, if you're writing a console application, it's a good idea to always explain WHY a program is waiting for input.
Any non-integer will stop the loop condition. In this case the syntax will work as-is, the user just needs some instruction:
System.out.println("Please enter the target");
int target = in.nextInt();
System.out.println("Enter weights. Type 'X' to stop");
while(in.hasNextInt()) {
How does this conditional statement (from Udacity's Intro to Java Programming | Problem Set 4 | Question #20) work?
import java.util.Scanner;
public class MonthPrinter {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
System.out.print("Enter a month number (1 through 12) ");
if (!in.hasNextInt()) {
System.out.println("Not an integer. Terminating");
} else {
int theMonthNumber = in.nextInt();
if (!(theMonthNumber >= 1 && theMonthNumber <= 12)) {
System.out.println("Number must be 1 through 12");
} else {
Month test = new Month(theMonthNumber);
System.out.print(test.getMonthName() + " " + test.getNumberOfDays());
}
}
}
}
The first if (!in.hasNextInt()) checks to see if the user input is an integer. If it's NOT an integer, the main method prints Not an integer. Terminating. That makes complete sense.
However, in the event that the user inputs an integer, the code proceeds to the else statement where the next line of code is int theMonthNumber = in.nextInt();
When the program runs and I provide an integer as an input, I'm NOT prompted for another input. I'm thinking that both the hasNextInt() method and nextInt() method should request an input from the user. Therefore, I should be prompted for a total of two inputs (assuming I provide an integer). When I dry-run this scenario, I input an integer 3. This passes the if(!hasNextInt()) check.
What am I missing in the logical flow of the statement(s)?
I'm thinking in my mind that both the hasNextInt() method and nextInt() method should request an input from the user.
No. The Scanner.hasNextInt() Javadoc says (in part)
Returns true if the next token in this scanner's input can be interpreted as an int value in the default radix using the nextInt() method. The scanner does not advance past any input.
The last sentence is telling you that it does not consume the int.
Function hasNextInt() is just for checking the input value. It will not consume the input. What happens is, it will advance the Scanner and check the data but after that it will go back to it's previous position. So technically, the position of Scanner has not changed. That's why it's not prompting for next input.
Only nextInt() will consume the data. Scanner will advance to the next position after calling this function.
I am making a program that will read user input and determine with an if/else condition what to do. If the user hits just enter and doesn't type anything else in, I want to loop something through the if. If anything else is typed as an input, the program should exit back to a different menu.
Here is what I have so far:
Scanner scnr = new Scanner(System.in);
String choice = scnr.next();
if (choice.equals("")) {
...
}
else {
...
}
When I run through it, just pressing enter does not affect anything, it just makes the cursor advance to the next line in the console. However, when I type something in, the error part that sends it to the menu when anything else is typed in works just fine. I'm thinking I have to use something besides scnr.next(); but I don't know what that would be.
This is for an entry level class, and it requires that we use the scanner utility and not something more advanced. Thanks in advance.
do
{
//string variable used to take scanner input when
//looping generations
String choice = "";
printWorld( patternName, world, generationCounter);
System.out.println("Options");
System.out.println("(Enter): show next generation");
System.out.println("end(Enter): end this simulation");
System.out.print("Choice:");
choice = scnr.nextLine();
if (choice.length() == 0) {
//used as a filler array when the method
//next generation is called
boolean newWorld[][] = new boolean [world.length][world[0].length];
nextGeneration(world, newWorld);
for (int i=0; i<newWorld.length;i++){
for (int j = 0; j<newWorld[0].length; j++){
world [i][j] = newWorld[i][j];
}
}
generationCounter++;
System.out.println("went through");
} else {
generationKill = 1;
generationCounter = 1;
}
} while (generationKill !=1);
Try using scnr.nextLine(); instead of scnr.next();
The reason for this is because of tokens. next()'s documentation says:
public String next()
Finds and returns the next complete token from this scanner.
Token generally is separated by whitespaces ("\n", "\t", " ") and therefore will not recognize your "enter" or "\n" character as a token. Which is why it'll keep reading, thinking that you haven't entered any tokens.
nextLine() on the other hand will read until it finds a "\n" character. That means when you enter, it's reading in a "\n" character, thereby setting your choice to be "".
I am having a little problem with my code. Compiling and running works well, however, when I attempt to break out of the inner loop,
System.out.println("Type which category you want to add to.");
System.out.println("Homework, Classwork, Labs, Test, Quizzes, Midterm, Final");
The code above is printing twice to the terminal when I only want it to print once.
I have a feeling that is a simple mistake with the way my brackets are aligned but I am having difficulty with figuring out how to do it. Any help would be greatly appreciated!
import java.util.Scanner;
public class GetGrade {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
final int MAX = 15;
int[] homework = new int[MAX];
int[] classwork = new int[MAX];
int[] lab = new int[MAX];
int[] test = new int[MAX];
int[] quizzes = new int[MAX];
int[] midterm = new int[MAX];
int[] fin = new int[MAX];
int hwCount, clCount, labCount, testCount, quizCount, midCount, finCount;
double hwTotal, clTotal, labTotal, testTotal, quizTotal, midTotal, finTotal;
double grade = 0;
String selection = "";
System.out.println();
System.out.println("Welcome to GetGrade!");
System.out.println();
while (true) {
System.out.println("Type which category you want to add to.");
System.out.println("Homework, Classwork, Labs, Test, Quizzes, Midterm, Final");
selection = input.nextLine();
if (selection.equals("homework")) {
System.out.print("What percentange of your grade is homework? > ");
double hwPercent = input.nextDouble();
System.out.println("Now begin typing your grades. When you are finished, type -1.");
for (int i = 0; i < homework.length; i++) {
homework[i] = input.nextInt();
hwTotal = homework[i] * hwPercent;
grade += hwTotal;
if (homework[i] == -1) break;
}
}
}
}
}
It's just as trivial as it seems:
The call to input.nextInt(); in your inner loop does not include the newline.
So you are breaking of the innerloop, receiving the next line which only contains the newline - character in input.nextLine(); which is the remaining input of your "-1\n" line and proceed with the main loop again as it does not match "homework".
Try setting the conditional variable in your while loop to an actual boolean rather than true.
Also, when you invoke "break", you are only breaking out of the for loop. If you reassign a boolean variable to false at this point, you would exit the while loop completely.
Just before while loop ends, add a "Do you want to continue? (Y/N)" functionality.
If user enters "N" or anything else, execute another break. And that break will make you get out of the while loop.
The simple way to get your code working is to change
selection = input.nextLine();
to
selection = input.next();
next() only reads in a string value (which is what you are actually doing in your code) instead of the newline character as Peter has suggested.
So the an extra iteration of the while does not take place when you read the newline character.
When you use a scanner to read a line from the keyboard, it reads everything up to and including the newline character the user types to submit their input. So for example:
Type which category you want to add to.
Homework, Classwork, Labs, Test, Quizzes, Midterm, Final
>
If you type "homework" and then ENTER, the actual input becomes "homework\n". input.nextLine() will scan the input until it encounters the first newline character, '\n', which it will consume and then it returns everything up to that point (i.e. "homework").
Your problem here is that input.nextInt() does NOT consume a newline character, and so there is still a newline character in the input buffer by the time your while loop starts another round.
Now begin typing your grades. When you are finished, type -1.
> ...
> -1
=> User input is "-1\n"
-------------------------------
// Meanwhile, back in the code...
for (int i=0;i<homework.length;i++) {
homework[i] = input.nextInt(); // <--- This call consumes "-1" but leaves '\n'
hwTotal = homework[i] * hwPercent;
grade += hwTotal;
if (homework[i] == -1) break;
}
That newline is consumed by the next call to input.nextLine(), leaving the input buffer empty.
while (true) {
System.out.println("Type which category you want to add to.");
System.out.println("Homework, Classwork, Labs, Test, Quizzes, Midterm, Final");
selection = input.nextLine(); // <--- This call consumes the leftover '\n' and returns the empty string
...
And because "" is not equal to "homework", the while loop goes around one more time, but this time the input buffer is empty, and so the call to input.nextLine() behaves as you would expect.
// selection is empty, so this condition fails and the program loops back around
if (selection.equals("homework")) {
...
There are two easy solutions to this problem. You can
Use Integer.parseInt(input.nextLine()) instead of input.nextInt()
Add an extra call to input.nextLine() at the end of your while loop to consume the final newline character
The first option is probably the most robust, and you get the added benefit of a run-time error being thrown if they do not give you a valid integer as input.