Java Scanning Basics

Java Scanning Basics

üA Scanner reads tokens from the underlying source.

üA token is a portion of input that is delineated by a set of delimiters, which is by default whitespace.

üA token is read by matching it with a particular regular expression.

üScanner follow the procedure below:

  1. Determine if a specific type of input is available by calling one of the hasNextX methods.

  2. If input is available, read it by calling one of nextX method.

      3. Repeat the process until the input is exhausted.

Note: if nextX() method does not find a matching token, it throws

 a NoSuchElementException.

Important Methods of Scanner Class

public Scanner(InputStream in)  // Scanner(): convenience constructor for an InputStream object

   

boolean hasNext()        //Return true if another token of any type is available to be read.

boolean hasNextBoolean()   //Return true if a boolean value is available to read.

boolean hasNextByte()        //Return true if a byte value is available to read.

boolean hasNextShort()     //Return true if a byte value is available to read.

boolean hasNextInt()        //Return true if a int value is available to read.

boolean hasNextLong()     //Return true if a long value is available to read.

boolean hasNextFloat()     //Return true if a float value is available to read.

boolean hasNextDouble()     //Return true if a double value is available to read.

Important Methods of Scanner Class

int nextInt()                      // return next token as int value.

short nextShort()         // return next token as short value.

byte nextByte()                     // return next token as byte value.

long nextLong()                  // return next token as long value.

double nextDouble()          // return next token as double value

float nextFloat()                // return next token as float value

String next()               //return next token of any type from the 

input source

String nextLine()             // return the next line of input as a 

string

Taking Input from the File

üThe following lines read data from a file:

  FileReader fin = new FileReader(“c:\\f_input.txt”);

    Scanner test = new Scanner(fin);

üFileReader:

   - belongs to java.io package.

   -It creates an object that can read the content of a file.

Taking Input from the File

import java.io.*;

import java.util.*;

}

class file_input

{

  public static void main(String args[]) throws IOException

  {

  double i;

  String str;

   

               FileReader fin = new FileReader("c:\\f_input.txt");

 

  Scanner test = new Scanner(fin);

 

  while(test.hasNext())

  {

  if(test.hasNextDouble())

  {

  i=test.nextDouble();

  System.out.println("The number is:" + i); 

  }

  else

  {

                         str = test.next();

  System.out.println(str);

  }

  }

                fin.close();

  }

}

Taking Input from a File

Suppose the file contains the following data:

2 3.4 5 6 7.4 9.1 10.5 done

Output:

The number is: 2.0

The number is: 3.4

The number is: 5.0

The number is: 6.0

The number is: 7.4

The number is: 9.1

The number is: 10.5

done

Writing Data into a File

import java.io.*;

class test

{

  public static void main (String args[])

  {

  FileWriter fout = new FileWriter(“c:\\test1.txt”);

  fout.write(“2 3.4 5 6 7.4 9.1 10.5 done”);

  fout.close();

     }

}