Java Scanner Class

In this tutorial, we will learn about the Java Scanner and its strategies with the help of examples.

The Scanner class of the java. util package is used to read input data from various sources like input streams, users, files, and so on. let’s take an example.

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Example 1: Read a Line of Text Using Scanner

import java.util.Scanner;

class Main {
  public static void main(String[] args) {

    // creates an object of Scanner
    Scanner input = new Scanner(System.in);

    System.out.print("Enter your name: ");

    // takes input from the keyboard
    String name = input.nextLine();

    // prints the name
    System.out.println("My name is " + name);

    // closes the scanner
    input.close();
  }
}

Output

Enter your name: salman
My name is salman

In the above example, notice the line

Scanner input = new Scanner(System.in);

Here, we have made an object of Scanner named input.

The System.in parameter is used to take input from the standard input. It works much the same as taking inputs from the keyboard.

We have then used the nextLine() strategy for the Scanner class to read a line of text from the user.

Since you have some idea about Scanner, let’s explore more about it.

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Import Scanner Class

As should be obvious from the above example, we need to import the java.util.Scanner package before we can use the Scanner class.

import java.util.Scanner;

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Make a Scanner Object in Java

When we import the package, here is the means by which we can make Scanner objects.

// read input from the input stream
Scanner sc1 = new Scanner(InputStream input);

// read input from files
Scanner sc2 = new Scanner(File file);

// read input from a string
Scanner sc3 = new Scanner(String str);

Here, we have made objects of the Scanner class that will read input from InputStream, File, and String individually.

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Java Scanner Methods to Take Input

The Scanner class provides various methods that allow us to read inputs of different types.

Method	Description
nextInt()	reads an int value from the user
nextFloat()	reads a float value form the user
nextBoolean()	reads a boolean value from the user
nextLine()	reads a line of text from the user
next()	reads a word from the user
nextByte()	reads a byte value from the user
nextDouble()	reads a double value from the user
nextShort()	reads a short value from the user
nextLong()	reads a long value from the user

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Example 2: Java Scanner nextInt()

import java.util.Scanner;

class Main {
  public static void main(String[] args) {

    // creates a Scanner object
    Scanner input = new Scanner(System.in);

    System.out.println("Enter an integer: ");

    // reads an int value
    int data1 = input.nextInt();

    System.out.println("Using nextInt(): " + data1);

    input.close();
  }
}

Output

Enter an integer:
22
Using nextInt(): 22

In the above example, we have used the nextInt() technique to read a integer value.

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Example 3: Java Scanner nextDouble()

import java.util.Scanner;

class Main {
  public static void main(String[] args) {

    // creates an object of Scanner
    Scanner input = new Scanner(System.in);
    System.out.print("Enter Double value: ");

    // reads the double value
    double value = input.nextDouble();
    System.out.println("Using nextDouble(): " + value);

    input.close();
  }
}

Output

Enter Double value: 33.33
Using nextDouble(): 33.33

In the above example, we have used the nextDouble() technique to read a floating point value.

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Example 4: Java Scanner next()

import java.util.Scanner;

class Main {
  public static void main(String[] args) {

    // creates an object of Scanner
    Scanner input = new Scanner(System.in);
    System.out.print("Enter your name: ");

    // reads the entire word
    String value = input.next();
    System.out.println("Using next(): " + value);

    input.close();
  }
}

Output

Enter your name: Salman Khan
Using next(): Salman

In the above example, we have used the next() technique to read a string from the user.

Here, we have given the complete name. However, the next() technique just reads the first name.

This is on the grounds that the next() strategy reads input up to the whitespace character. When the whitespace is experienced, it returns the string (excluding the whitespace).

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Example 5: Java Scanner nextLine()

import java.util.Scanner;

class Main {
  public static void main(String[] args) {

    // creates an object of Scanner
    Scanner input = new Scanner(System.in);
    System.out.print("Enter your name: ");

    // reads the entire line
    String value = input.nextLine();
    System.out.println("Using nextLine(): " + value);

    input.close();
  }
}

Output

Enter your name: Salman Khan
Using nextLine(): Salman Khan

In the first example, we have used the nextLine() strategy to read a string from the user.

Not at all like straightaway(), the nextLine() technique reads the whole line of input including spaces. The strategy is ended when it encounters a next line character, \n.

Recommended Reading: Java Scanner skipping the nextLine().

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Java Scanner with BigInteger and BigDecimal

Java scanner can also be used to read the big integer and big decimal numbers.

• nextBigInteger() – reads the big integer value from the user
• nextBigDecimal() – reads the big decimal value from the user

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Example 6: Read BigInteger and BigDecimal

import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.Scanner;

class Main {
  public static void main(String[] args) {

    // creates an object of Scanner
    Scanner input = new Scanner(System.in);
    System.out.print("Enter a big integer: ");

    // reads the big integer
    BigInteger value1 = input.nextBigInteger();
    System.out.println("Using nextBigInteger(): " + value1);

    System.out.print("Enter a big decimal: ");

    // reads the big decimal
    BigDecimal value2 = input.nextBigDecimal();
    System.out.println("Using nextBigDecimal(): " + value2);

    input.close();
  }
}

Output

Enter a big integer: 987654321
Using nextBigInteger(): 987654321
Enter a big decimal: 9.55555
Using nextBigDecimal(): 9.55555

In the above example, we have used the java.math.BigInteger and java.math.BigDecimal package to read BigInteger and BigDecimal individually.

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Working of Java Scanner

The Scanner class reads a whole line and partitions the line into tokens. Tokens are little components that make them intend to the Java compiler. For instance,

Assume there is an input string:

He is 22

For this situation, the scanner object will read the whole line and partitions the string into tokens: “He“, “is” and “22“. The object at that point repeats over every token and reads each token using its various strategies.

Note: By default, whitespace is used to divide tokens.

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