I'm doing a simple program regarding methods.
But I have one problem. Everything is already working except when looping.
When I choose to loop again. The program skips on inputting the name. And proceeds directly to the year and section.
Here's the code:
public static void main(String[] args) {
do{
System.out.println("Input info:");
name=stringGetter("Name: ");
yearandsec=stringGetter("Year and section: ");
sex_code=charGetter("Sex code: " + "\n" + "[M]" + "\n" + "[F]:");
scode=intGetter("Scholarship code: ");
ccode=intGetter("Course code: ");
units=intGetter("Units: ");
fee_per_unit=doubleGetter("Fee per unit: ");
misc=doubleGetter("Miscellaneous: ");
display();
switches(scode, units, fee_per_unit, misc);
System.out.println("Another?");
dec=rew.nextInt();
}while(dec==1);
}
Here's the method getting the value for name together with the year and section:
public static String stringGetter(String ny){
String sget;
System.out.println(ny);
sget=rew.nextLine();
return sget;
}
I'm really annoyed with this problem, and I don't have any idea on how to fix this. Please help. thanks
Here is a simpler and more complete program that reproduces the error:
public static Scanner rew = new Scanner(System.in);
public static void main(String[] args) {
int dec;
do {
System.out.println("Input info:");
String name=stringGetter("Name: ");
String yearandsec=stringGetter("Year and section: ");
dec=rew.nextInt();
} while(dec==1);
}
public static String stringGetter(String ny){
System.out.println(ny);
return rew.nextLine();
}
The problem is that after calling nextInt() the call to nextLine() reads up to the new line after the int (giving a blank line), not up to the next new line.
If you change dec to a String and change dec=rew.nextInt(); to dec=rew.nextLine(); then it will work fine. Here is a complete example that you can copy and paste into a blank file to see that it works correctly:
import java.util.*;
public class Program
{
public static Scanner rew = new Scanner(System.in);
public static void main(String[] args) {
String dec;
do {
System.out.println("Input info:");
String name = stringGetter("Name: ");
String yearandsec = stringGetter("Year and section: ");
dec = stringGetter("Enter 1 to continue: ");
} while(dec.equals("1"));
}
public static String stringGetter(String ny){
System.out.println(ny);
return rew.nextLine();
}
}
You may also want to consider adding proper parsing and validation to your program. Currently your program will behave in an undesirable way if the user enters invalid data.
The line:
dec = rew.nextInt();
Is reading an int value from the input stream and is not processing the newline character, then when you come back to point where you get the name at which point a new line is still in the Reader's buffer and gets consumed by the stringGetter returning an empty value for name.
Change the line to do something like:
do {
//....
s = stringGetter("Another (y/n)? ");
} while ("y".equals(s));
Well you haven't told us what "rew" is, nor what rew.nextInt() does. Is it possible that rew.nextInt() is waiting for the user to hit return, but only actually consuming one character of the input - so that the next call to rew.nextLine() (for the name) just immediately takes the rest of that line? I suspect that's what's happening because you're using System.in - usually reading from System.in only gives any input when you hit return.
(It's possible that this is also only a problem on Windows - I wonder whether it consumes the "\r" from System.in as the delimiter, leaving "\n" still in the buffer. Not sure.)
To test this, try typing in "1 Jon" when you're being asked whether or not to continue - I think it will then use "Jon" as the next name.
Essentially, I think using Scanner.nextInt() is going to have issues when the next call is to Scanner.nextString(). You might be better off using a BufferedReader and calling readLine() repeatedly, then parsing the data yourself.
Related
I have a command-line game and am testing with JUnit, this is the test:
#Test
public void testBattle() throws IOException{
String input = "go forward\ngo left\ntake Pointy Stick\ngo backward\ngo " +
"right\nnormal attack\nnormal attack\nquit\n";
provideInput(input);
actual = new File("src/main/testFiles/testBattle.txt");
expected = new File("src/main/testFiles/testBattleExpected.txt");
PrintStream o = new PrintStream(actual);
System.setOut(o);
ui.gameLoop();
assertTrue(FileUtils.contentEqualsIgnoreEOL(actual, expected, null));
}
And this is the provide input method:
private void provideInput(String data) {
String newdata = data.trim();
testIn = new ByteArrayInputStream(newdata.getBytes());
System.setIn(testIn);
}
I'm doing scanner nextline so:
command = input.nextLine().toLowerCase().trim();
where "input" here represents the scanner object
but I'm still getting this error, specifically when the first "normal attack" is passed into System.in
java.util.NoSuchElementException: No line found
on that line above. I thought nextline ignored whitespace? If not did I format my string wrong to not include it?
EDIT:
From the first few lines of UI.gameLoop() I only initialize the scanner once.
public void gameLoop() throws IOException, JsonSyntaxException {
input = new Scanner(System.in);
engine = new GameEngine(path);
I thought nextline ignored whitespace?
Nope. According to the javadocs, it reads past the next end-of-line sequence (or to EOF), and then returns everything up to but not including the end-of-line sequence.
If you are getting
java.util.NoSuchElementException: No line found
that means that the Scanner has already reached the end of the input stream, or (maybe) the Scanner is trying to read from an input stream that was prematurely closed somewhere else in your code.
We can make guesses about what the real problem is, but without seeing >>your<< minimal reproducible example, we can't take this much further.
Actually, I just spotted a clue:
... I am testing with JUnit ...
This is possibly at the root of your problems. A JVM can only "read to the end of System.in" once in its lifetime. If you have two or more JUnit tests that need to do this, it is going to be difficult, unless you can find a way to "mock" the System.in variable.
It may be simpler to reorganize your code so that you take the input from some stream that is passed to your game code as a parameter. By reorganizing you can make it easier to write unit tests.
There's not a lot to go on, but I'm guessing you're creating multiple Scanners, one for each time you want to read a line. This usually works ok interactively since humans are slow typers, but fails when each Scanner's readahead ends up consuming multiple lines.
You can see the difference in this MCVE:
import java.util.*;
import java.io.*;
class Foo {
public static void main(String[] args) throws Exception {
String newdata = "go forward\ngo left\ntake Pointy Stick\ngo backward\ngo " +
"right\nnormal attack\nnormal attack\nquit\n".trim();
ByteArrayInputStream testIn = new ByteArrayInputStream(newdata.getBytes());
System.setIn(testIn);
boolean includeBug = Boolean.valueOf(args[0]);
if (includeBug) {
for(int i=0; i<8; i++) {
Scanner input = new Scanner(System.in);
System.out.println("Read: " + input.nextLine());
}
} else {
Scanner input = new Scanner(System.in);
for(int i=0; i<8; i++) {
System.out.println("Read: " + input.nextLine());
}
}
}
}
When includeBug is true, it creates a new Scanner for each line and crashes like you say. If it's false, it creates a single Scanner and works correctly:
$ javac Foo.java
$ java Foo true
Read: go forward
Exception in thread "main" java.util.NoSuchElementException: No line found
at java.util.Scanner.nextLine(Scanner.java:1540)
at Foo.main(Foo.java:17)
$ java Foo false
Read: go forward
Read: go left
Read: take Pointy Stick
Read: go backward
(etc)
Are you checking if it has a next line? With Scanners, you usually either have to handle the exception (not really something I'd prefer) or you have to use the hasNextLine() method to avoid the exception.
while (input.hasNextLine()) {
command = input.nextLine().toLowerCase().trim();
}
I'm pretty new to Java coming from Python so please pardon my retardedness. I'm trying to make a simple if statement and it won't work :(. It ignores the if statement and goes straight else.
I've tried to use .contains and .equalsIgnoreCase in the if statement.
package me.johnminton;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner user_input = new Scanner(System.in);
String species_animal;
System.out.println("Please enter your species: ");
species_animal = user_input.next();
if (species_animal.contains("Erectus")) {
System.out.println("random input statement");
}
else
{
System.out.println("okay");
}
}
}
I'm hoping for it output "random input statement" if I input Erectus in the first input. But instead, it goes straight to the else and outputs "okay".
The next() method just fetches a single word from the scanner, although you can change that behaviour by specifying a delimiter for the scanner.
In your case, if you type Eructussian or something similar, you'll get the result you want, but if you type Home Erectus, you won't.
I suspect you meant to use nextLine() instead of next(), which fetches an entire line of text.
The problem is that your scanner isn’t finishing without getting a return key. Try ‘user_input.nextLine()’ instead of ‘user_input.next()’
I started doing the CodeAbbey problems last night, they mentioned using stdIn since some the input data is long so copy/paste is much easier than by hand. I had never used the Scanner before so it looked easy enough. I got it working for single line inputs then I got a problem where the input was:
867955 303061
977729 180367
844485 843725
393481 604154
399571 278744
723807 596408
142116 475355
I assumed that nextLine would read each couple, xxxx yyyyy. I put the code in a while loop based on if nextLine is not empty. It runs, but I get weird output, and only after I hit return a few times.
package com.secryption;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
System.out.println("Input: ");
Scanner scanner = new Scanner(System.in);
String input = "";
while(!(scanner.nextLine().isEmpty())) {
input = input + scanner.nextLine();
}
String[] resultSet = input.split("\\s+");
for(String s : resultSet) {
System.out.println(s);
}
}
}
I thought I might need something after adding scanner.nextLine() to input. I tried a space and that didn't help. I tried a newline and that didn't make it better.
This "should" put all the numbers in a single array, nothing special. What am I missing with scanner?
EDIT: Ok so #Luiggi Mendoza is right. I found this How to terminate Scanner when input is complete? post. So basically it it working, I just expected it to do something.
The problem is here:
while(!(scanner.nextLine().isEmpty())) {
input = input + scanner.nextLine();
}
Scanner#nextLine reads the line and will continue reading. You're reading two lines and not storing the result of the first line read, just reading and storing the results of the second.
Just change the code above to:
StringBuilder sb = new StringBuilder();
while(scanner.hasNextLine()) {
sb.append(scanner.nextLine()).append(" ");
}
hasNext() is an end of file indicator that terminates by combining keys control d on Mac ox and control z on windows pressing enter won't send the right message
to JVM
This program goes in an infinite loop in while cycle. Please, can someone tell me why?
import java.util.Scanner;
public class program {
public static void main(String[] pars) {
System.out.println("Insert something.");
Scanner read = new Scanner(System.in);
String s = "";
while(read.hasNext()) {
System.out.println(read.next());
}
System.out.println("End of program");
}
}
Read the Javadoc of Scanner#hasNext():
Returns true if this scanner has another token in its input. This method may block while waiting for input to scan. The scanner does not advance past any input.
Hence the while loop will always be executed in your case, each time waiting for input from the user. Since the Scanner is linked to System.in, the input stream will always block until the user inputs a string and hasNext() will always return true, unless the user signals the end of file (e.g. through the Ctrl+z combination on Windows). Scanner#hasNext() is more convenient when reading from files where the input size is known and the end of the file marks the end of the stream.
One way to end the loop here is to add a condition on the input:
while (read.hasNext()) {
s = read.next();
if(s.equals("quit")) {
break;
}
System.out.println(s);
}
P.S.: It is more conventional to name classes starting with an uppercase letter.
The problem is this line:
while(read.hasNext()) {
If you use System.in as a stream provided by the user, it will - if no such input is available - as #manouti says, block and wait for input. But even if you provide input, it will keep waiting. The system has no means to detect whether the user wants to provide additional input in the future.
It will only stop, if the Stream ends. This can be under two conditions:
The end of the file (in case of I/O redirection like java -jar program.jar < input.dat; or
The user marks the end of a stream, in most shells with Ctrl+D. This marks the end-of-stream.
An alternative is to provide some kind of stop directive. Something like "END". Thus:
while(read.hasNext()) {
String nx = read.next();
if(nx.equals("END")) {
break;
}
System.out.println(nx);
}
Just remove while loop
public static void main(String[] pars) {
System.out.println("Insert something.");
Scanner read = new Scanner(System.in);
String s = "";
System.out.println(read.next());
System.out.println("End of program");
}
Or if u want display certain no.of string then mention condition properly.
public static void main(String[] pars) {
System.out.println("Insert something.");
Scanner read = new Scanner(System.in);
String s = "";
int i=0;
while(i<5) {
System.out.println(read.next());
i++;
}
System.out.println("End of program");
}
I'm making a program that reads a person's name and age, and when "zzz" is entered, it prints the names and ages of everyone who's 18 or older. Also, I want to calculate the percentage of people who's 18 or older. But, here's the problem: the code i'm posting bellow, only prints the first name (example: "Ricardo Almeida" and age "19". Output: "Ricardo : 19", but i want "Ricardo Almeida : 19). The percentage calculation has a error too but i cant figure out whats wrong. It gives 0 all the times. (DONE!) Thanks in advance to anyone who's reading this and trying to help.
PS: I dont want to use arrays! I already learned how to use them, but i want to know how to solve this without using them :)
package javaapplication38;
import java.util.Scanner;
public class JavaApplication38 {
private static final Scanner in=new Scanner(System.in);
private static String metodo1(String name, int age) {
String frase="";
if (age==18 | age>18) {
frase=String.format("%s : %d %n",name,age);
}
return frase;
}
public static void main(String[] args) {
int age, counter1=0, counter2=0;
String name, acumtxt="", aux;
do {
System.out.print("Name: ");
name=in.next(); in.nextLine();
if (!"ZZZ".equalsIgnoreCase(name)) {
counter1++;
do {
System.out.print("Age: ");
age=in.nextInt();
} while (age<=0);
if (age==18 | age>18) {
counter2++;
}
aux=metodo1(name,age);
acumtxt+=aux;
}
} while(!"ZZZ".equalsIgnoreCase(name));
System.out.print(acumtxt);
if (counter1>0) {
System.out.println("The percentage of people who's 18 or older is "+ (counter2/counter1) +"%.");
}
}
}
It seems that your problem is here
name=in.next(); in.nextLine();
In this code next() reads and returns only one word from line until it finds whitespace or end of line. Rest of it is consumed with readLine(), but you ignore its result. Try maybe to with
name=in.nextLine();
to read entire line.
After that you will also have to change
age=in.nextInt();
and either use
age=Integer.parseInt(in.nextLine());
or add in.nextLine() after it to also consume new line marks which would affect next name question.
age=in.nextInt(); in.nextLine();//add in.nextLine(); to consume new line marks
in.next() will read until there is a whitespace. You can use in.nextLine (http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html#nextLine()) or use [BufferedReader](http://docs.oracle.com/javase/7/docs/api/java/io/BufferedReader.html) instead, and you can call the readLine() method.