Java Scanner class

Introduction

Java Scanner class reads formatted input and returns it to you.

We can use Scanner class to read input from the console, a file, a string, or any source that implements the Readable interface or ReadableByteChannel.

A Scanner can be created for a String, an InputStream, a File, or any object that implements the Readable or ReadableByteChannel interfaces.

The following sequence creates a Scanner that reads the file Test.txt: 

FileReader fin = new FileReader("Test.txt");  
Scanner src = new Scanner(fin);

FileReader implements the Readable interface.

Thus, the call to the constructor resolves to Scanner(Readable).

The following line creates a Scanner that reads from standard input, which is the keyboard by default: 

Scanner conin = new Scanner(System.in);

System.in is an object of type InputStream. The call to the constructor maps to Scanner(InputStream).

The next sequence creates a Scanner that reads from a string. 

String instr = "10 1.8 string from demo2s.com.";  
Scanner conin = new Scanner(instr);

Scanning

To use Scanner, follow this procedure:

  • Determine if a specific type of input is available by calling one of Scanner's hasNextXXX() methods.
  • If input is available, read it by calling one of Scanner's nextXXX() methods.
  • Repeat the process until input is exhausted.
  • Close the Scanner by calling close().

The following sequence shows how to read a list of integers from the keyboard. 

Scanner conin = new Scanner(System.in);  
int i;  
         
// Read a list of integers.  
while(conin.hasNextInt()) {  
    i = conin.nextInt();  
    // ...  
} 

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scannerObject = new Scanner(System.in);

        System.out.println("Enter two whole numbers");
        System.out.println("separated by one or more spaces:");

        int n1, n2;
        n1 = scannerObject.nextInt();//  w w  w  .j  a va 2  s . c  o m
        n2 = scannerObject.nextInt();
        System.out.println("You entered " + n1 + " and " + n2);

        System.out.println("Next enter two numbers.");
        System.out.println("A decimal point is OK.");

        double d1, d2;
        d1 = scannerObject.nextDouble();
        d2 = scannerObject.nextDouble();
        System.out.println("You entered " + d1 + " and " + d2);

        System.out.println("Next enter two words:");

        String s1, s2;
        s1 = scannerObject.next();
        s2 = scannerObject.next();
        System.out.println("You entered \"" + s1 + "\" and \"" + s2 + "\"");

        s1 = scannerObject.nextLine(); //To get rid of '\n'

        System.out.println("Next enter a line of text:");
        s1 = scannerObject.nextLine();
        System.out.println("You entered: \"" + s1 + "\"");
    }
}



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