I have declared two strings and reading the input using Scanner(System.in).
After this when i am closing the Scanner and again reading the another input using the Scanner,then it throws an error: NoSuchElementException.
Please guide me on this
import java.util.Scanner;
import java.io.*;
public class NumericInput
{
public static void main(String[] args)
{
// Declarations
Scanner in = new Scanner(System.in);
String string1;
String string2;
// Prompts
System.out.println("Enter the value of the First String .");
// Read in values
string1 = in.nextLine();
// When i am commenting below line(in.close) code is working properly.
in.close();
Scanner sc = new Scanner(System.in);
System.out.println("Now enter another value.");
string2 = sc.next();
sc.close();
System.out.println("Here is what you entered: ");
System.out.println(string1 + " and " + string2);
}
}
When you close your scanner it also closes System.in input stream, you are using it again, but it's closed, so when you try to use Scanner again, no open System.in stream is found.
There is no need to close a Scanner, since it implements AutoCloseable interface you should declare resources in try-with-resources as of java 7. If closing Scanner is an issue.
try(Scanner in = new Scanner(System.in); Scanner sc = new Scanner(System.in)){
// do stuff here without closing
}
catch(Exception){
e.printStackTrace();
}
Related
I have two versions of Java code that gets user input until user types "q"
Version 1:
public class Test {
public static void main(String[] args) {
String input = "";
while (!input.equals("q")) {
Scanner scanner = new Scanner(System.in);
System.out.print("Input: ");
input = scanner.nextLine();
System.out.println("Input was: " + input);
}
}
}
Version 2:
public class Test {
public static void main(String[] args) {
String input = "";
while (!input.equals("q")) {
try(Scanner scanner = new Scanner(System.in)){
System.out.print("Input: ");
input = scanner.nextLine();
System.out.println("Input was: " + input);
}
}
}
}
Version 1 works as expected but version 2 does not work as expected.
That is after reading user input for the first time, it produces an error
Input: 12
Input was: 12Exception in thread "main"
Input: java.util.NoSuchElementException: No line found
at java.util.Scanner.nextLine(Scanner.java:1540)
at RealEstateCompany.main(RealEstateCompany.java:115)
My guess is since version 2 uses try with resource so it closes the scanner after being used and that is causing an error?
Thank you for your help in advance!
[Update]
Version 3:
public class Test {
public static void main(String[] args) {
String input = "";
try(Scanner scanner = new Scanner(System.in)){
while (!input.equals("q")) {
System.out.print("Input: ");
input = scanner.nextLine();
System.out.println("Input was: " + input);
}
}
}
}
Version 3 works. However, why version 3 is ok and version 2 is not ok?
Adding a little bit more detail to my comments
A try-with block is defined as follows:
try(...) {
...
}
where the argument in parenthesis needs to be an instance of java.lang.AutoCloseable. An example is the class java.io.InputStream, which is also the class for System.in.
A try-with attempts to automatically close its provided resource, once the block is left. Depending on the used resource, it closes all its own child resources as well.
Taking your example, you have try(Scanner scanner = new Scanner(System.in)), which uses Scanner as resource. The scanner itself uses System.in as resource. Once the try block is left (when } is reached) it tries to close its resources, which is the Scanner instance. This instance also tries to close its resource, the System.in.
Once System.in is closed, you can't get any input from the console anymore (at least not with some additional work, I think...).
Concretely, in your second example:
while (!input.equals("q")) {
try(Scanner scanner = new Scanner(System.in)){
...
} // <--- The block is left, scanner is closed, System.in is closed
} // <-- start a new iteration
Here after just one iteration, System.in gets closed. Sure, you create a new Scanner in the next iteration, but System.in remains closed, that's why you get your exception in this case.
Your third example:
try(Scanner scanner = new Scanner(System.in)){
while (!input.equals("q")) {
...
} // <-- start a new iteration, while still in the same try block
} // <-- only after the while, your resources are closed
Here you're looping your while, while still being inside try. So no resource gets closed, until you leave while and try. That means, the one Scanner remains intact and with it the one System.in. This allows you to keep reading from the console until you're done looping.
Try this:
String input = "";
try (Scanner scanner = new Scanner(System.in)) {
while (!input.equals("q")) {
System.out.print("Input: ");
input = scanner.nextLine();
System.out.println("Input was: " + input);
}
}
You can use every class thats implements Closeable or AutoCloseable in try-with-resources, When code reaches the end of the try call, It call close() function of the Scanner class in our example.
i run some tests and add the catch block into your code.here's the code
public static void main(String[] args) {
String input = "";
while (!input.equals("q")) {
try(Scanner scanner = new Scanner(System.in)){
System.out.print("Input: ");
input = scanner.nextLine();
System.out.println("Input was: " + input);
}
catch (Exception e) {
e.printStackTrace();
}
}
}
when add the catch block，there are 2 kinds of results
1,only inputs q, works as expected
2,inputs any other String, exception
Input: java.util.NoSuchElementException: No line found
at java.util.Scanner.nextLine(Scanner.java:1585)
at rews.pub.Test.main(Test.java:11)
when added the catch block, we will see that the program won't stop, because of the while loop
here is another easier test
public class Test {
public static void main(String[] args) {
String input = "";
Scanner scanner = new Scanner(System.in);
System.out.println("inout--1---");
input = scanner.nextLine();
scanner.close();
Scanner scanner2 = new Scanner(System.in);
System.out.println("inout--2---");
input = scanner2.nextLine();
scanner2.close();
}
}
and it goes same exception
inout--1---
11
inout--2---
Exception in thread "main" java.util.NoSuchElementException: No line found
at java.util.Scanner.nextLine(Scanner.java:1585)
at rews.pub.Test.main(Test.java:15)
here's my opinion.
in the end of first run, try()block will close the resource which is in the block, means we close the system.in
system.in is a object of inputSteam，and system.in is final and static, we can't open it again like 'new Scanner(System.in)'
I am an extreme beginner in Java and I can't seem to get the user input. I am using eclipse mars. My code:
import java.util.Scanner;
public class HelloWorld {
public static void main(String[] args) {
System.out.println("What is your name?");
Scanner UserName = new Scanner(System.in);
System.out.println(UserName);
}
}
You need to first create your Scanner, then call nextLine on it to get input from the user:
import java.util.Scanner;
class NameAsker {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("What is your name? ");
String userName = input.nextLine();
System.out.println("Your name is: " + userName);
}
}
try
System.out.println(UserName.nextLine());
Read Oracle docs for more info
you can use like.
Scanner input=new Scanner(System.in);
if you want to get integer.
int number=input.nextInt();
System.out.Println(number);
for String:
String str=input.nextLine();
There are other method for taking user input like bufferedReader and BufferedInputStream for more details check Java Docs.
This question already has answers here:
System.console() returns null
(13 answers)
Closed 7 years ago.
I want to input a name and to print the first char ....
public class Test {
public static void main(String[] args) {
Console console = System.console();
System.out.println("Type your name : ");
String inputChar = console.readLine();
char firstChar = inputChar.charAt(0);
System.out.println(firstChar);
}
}
Some IDEs will return NPE for Console class. you can use the Scanner class and do it easily:
try this:
Scanner scan = new Scanner(System.in);
System.out.println("Enter a Name:");
String s = scan.next();
System.out.println(s.charAt(0));
this will print the first letter of your input String.
Using the Console class can a bit unreliable at times.
For reading console input, it would be preferrable to use either the Scanner class or a BufferedReader.
You can use a Scanner like :
Scanner scanner = new Scanner(System.in); // System.in is the console's inputstream
System.out.print("Enter text : ");
String input = scanner.nextLine();
// ^^ This reads the entire line. Use this if you expect spaces in your input
// Otherwise, you can use scanner.next() if you only want to read the next token
System.out.println(input);
You can also use BufferedReader like :
pre Java 7 syntax
try {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
System.out.print("Enter text : ");
String input = br.readLine();
System.out.println(input);
br.close();
} catch (Exception e) {
e.printStackTrace();
}
Java 7 syntax
try (BufferedReader br = new BufferedReader(new InputStreamReader(System.in))) {
System.out.print("Enter text : ");
String input = br.readLine();
System.out.println(input);
} catch (Exception e) {
e.printStackTrace();
}
Note: You need to use a try-catch statement when calling br.readLine() because it throws an IOException.
You can use Scanner if you want to read tokens (chunks of text separated by spaces). Use a BufferedReader if you want to simply read from the InputStream.
So I am trying to search through a text file and if the user input is found, it returns the entire sentence including white spaces.But apparently I only get the first string and nothing pass the first string in the sentence. For example if i have a text file called "data.txt" and the contents in the first line is " I am a legend". after user enters "I am a legend" the output after the file is searched is "I". Any help would be appreciated.
public static void Findstr() { // This function searches the text for the string
File file = new File("data.txt");
Scanner kb = new Scanner(System.in);
System.out.println(" enter the content you looking for");
String name = kb.next();
Scanner scanner;
try {
scanner = new Scanner(file).useDelimiter( ",");
while (scanner.hasNext()) {
final String lineFromFile = scanner.nextLine();
if (lineFromFile.contains(name)) {
// a match!
System.out.println("I found " + name);
break;
}
}
} catch (IOException e) {
System.out.println(" cannot write to file " + file.toString());
}
package com.example;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class FileSearch {
public void parseFile(String fileName,String searchStr) throws FileNotFoundException{
Scanner scan = new Scanner(new File(fileName));
while(scan.hasNext()){
String line = scan.nextLine().toLowerCase().toString();
if(line.contains(searchStr)){
System.out.println(line);
}
}
}
public static void main(String[] args) throws FileNotFoundException{
FileSearch fileSearch = new FileSearch();
fileSearch.parseFile("src/main/resources/test.txt", "am");
}
}
test.txt contains:
I am a legend
Hello World
I am Ironman
Output:
i am a legend
i am ironman
The above code does case insensitive search. You should use nextLine() to get the complete line. next() breaks on whitespaces.
Reference:
http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html#next()
Scanner.next(); returns the next caracter instead use Scanner.readLine();
Edit:
Belive Scanners use .nextLine(); not .readLine();
When you are scanning your input..
Scanner kb = new Scanner(System.in);
System.out.println(" enter the content you looking for");
String name = kb.next();
You are accepting only one token. You should accept whole line to be searched as your token using kb.nextLine()
I tried to test 2 ways of getting data from user. I faced 2 errors, as I attached.
First error:
Second error:
I have second error (Obeject is never closed) with every object which I create from Scanner class!
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Scanner;
public class InputStreamReaderClass {
public static void main(String[] args) {
// Method 1:
InputStreamReader reader = new InputStreamReader(System.in);
BufferedReader buffer = new BufferedReader(reader);
System.out.println("Type text 1: ");
String text = buffer.readLine();
//Method 2:
Scanner scanner = new Scanner (System.in);
System.out.println("Type text 2: ");
String text2 = scanner.nextLine();
}
}
Method 1 you have to fix. You have to handle the error. The issue with the second method is a warning, and the program will still run without the fix, but it is a good idea to get in the habit of closing objects you're not using.
Method 1 needs to be surrounded by a try/catch statement, or you need to throw and exception:
try{
// Method 1:
InputStreamReader reader = new InputStreamReader(System.in);
BufferedReader buffer = new BufferedReader(reader);
System.out.println("Type text 1: ");
String line = buffer.readLine();
}catch(Exception e){
//handle error
}
This is because BufferedReader.readLine() throws an exception, and you need to handle it. You can get more info from the Java documentation
Method 2, you need to close the scanner object:
//Method 2:
Scanner scanner = new Scanner (System.in);
String line2 = scanner.nextLine();
System.out.println("Type text 2: ");
scanner.close();
You don't necessarily have to close the scanner, but it is a good practice.