Wednesday, November 19, 2014

Scanner Class tutorial with examples in java

Scanner Class tutorial with examples in java

In this blog post, I will covert the scanner class tutorials with examples ofJavaa language.

Basics Usage of Scanner class in java.

 Scanner class is one of the basic default classes provided by Java language as part of JDK installation. Scanner class is located in java.util package Java.util.Scanner class is one way to take the input from the keyboard in java. Scanner class read the input in the form of java primitive data types like Integer and String. Internally Scanner class in Java uses a regular expression to parse the input using default space delimiter. Scanner class introduced in Java 1.5 

Java.util.Scanner class declaration

Scannar.java class in JDK as the following declaration
public final class Scanner
extends Object
implements Iterator, Closeable
Scanner class implements Iterator and closeable interfaces.Iterator class used to iterate scanned primitive types, Closeable is used to release the resources once scanner read the source.

import java.util.Scanner;

public class ScannerExample {
      public static void main(String args[]) {
            Scanner readInput = new Scanner(System.in);
            String line = readInput.nextLine();
            System.out.println("Scanner Console Example= " + line);
      }
}
 And out put  is Scanner Console Example= Scanner Usage example if Scanner Usage example is provided as intput

Scanner examples in java 

We can use java.util.scanner class is used to read data from various source

How to read the input data from the console using Scanner class

Scanner API in Java provides a various constructor for reading various sources like File, InputStream, java.nio.file.Path, java.nio.channels.ReadableByteChannel System.in provides the reading capabilities to read from the console. This option provides capabilities to read data from console based on input data.

How to read the input data from File stream using Scanner class in java


Scanner constructor has as file reader reference to read input data from files.
Scanner fileScannerRead = new Scanner (new FileReader(new File("FILE_PATH")));

How to Fix NoSuchElementException using Scanner class 


NoSuchElementException exception is RuntimeException occurred when there is no element to scan while using Scanner class in java NoSuchElementException occurs when code has Scanner.next() method To fix this, code needs to check whether next element is available or not.
Scanner readInput = new Scanner(System.in);
if (readInput.hasNext()) {
                  Object obj = readInput.next();
            }

nextInt(),nextLong() methods also throws NoSuchElementException . To fix, Code has to use corresponding hasNextInt(),hasNextLong() methods.

Fixing Exception in thread "main" java.util.InputMismatchException 

The following example expects the input as a number from the console

Public static void main(String args[]) {
            Scanner readInput = new Scanner(System.in);
        System.out.print("Enter input number : ");
        int inputNo = readInput.nextInt();
}
Above program, prints read the integer number when integer number is provided. InputMismatchException exception throws when float number is provided as input. Please make sure that you enter the correct input data and handle the correct method to read data.

java.util.Scanner class advantages


  • Simplifies the text reading capabilities using the scanner class 
  • Scanner has default regular expression for primitive data types and String. So Regular expression compile is not required and hence improved the performance java.util.Scanner class 

Disadvantages 


  • Scanner is not good for multithread applications for thread safety.
  • Need to handle synchronization Java Compiler encountered Scanner class during execution, compiler wait until data is entered by the user.

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