java.util.Scanner – Scanner Java Example (with video)

In this example, we will show the range of functionality provided by the java.util.Scanner – Scanner Java class. We will also see how to use the Java Scanner class to read a Java input form the console. A simple text scanner which can parse primitive types and strings using regular expressions.

You can also check this tutorial in the following video:

1. Introduction

A Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace.

The resulting tokens may then be converted into values of different types using the various next methods.

For example, this code allows a user to read a number from System.in:

The scanner can also use delimiters other than whitespace. This example reads several items in from a string:

The following code shows you how you can use the Java Scanner class to read a Java input form the console. To start, you create a Scanner object passing System.in (which is the keyboard) as a parameter to the Constructor. Like the System.out object, the System.in object is created by Java automatically. Because of that, you can use this object with a Scanner object whenever you want to get a console input.

Once you’ve created a Scanner object, you can use the next methods to read data from the console. The method you use depends on the type of data you need to read. To read string data, for example, you use the next method. To read integer data, you use the nextInt method. To read double data, you use the the nextDouble method. And to read all of the data on a line, you use the nextLine method. When one of the methods of the Scanner class is run, the application waits for the user to enter data with the keyboard. To complete the entry, the user presses the Enter key.

Since the Scanner class is in the java.util package, you’ll want to include an import statement whenever you use this class.

2. Scanner Constructors

Here is a list of the Constructors in the Java scanner Class.

3. Scanner Methods

Here is a list of the Methods in the Java scanner class.

4. Scanner Java Example

Let’s see a Scanner Java Example.

JavaUtilScannerExample.java

Let’s explain the methods used in the above example.

• public Scanner(InputStream source) – Constructs a new Scanner that produces values scanned from the specified input stream. Bytes from the stream are converted into characters using the underlying platform’s default charset.
• public String next() – Finds and returns the next complete token from this scanner. A complete token is preceded and followed by input that matches the delimiter pattern. This method may block while waiting for input to scan, even if a previous invocation of hasNext() returned true.
• public double nextDouble() – Scans the next token of the input as a double. This method will throw InputMismatchException if the next token cannot be translated into a valid double value. If the translation is successful, the scanner advances past the input that matched.
• public int nextInt() – Scans the next token of the input as an int.

If we run the above code, we will get the following results:

5. Common use of java.util.Scanner class

A common programming task involves parsing a string of text into words or “tokens” that are separated by some set of delimiter characters, such as spaces or commas.

ScannerTokenizingText.java

Let’s explain the methods used in the above example.

• public float nextFloat() – Scans the next token of the input as a float. This method will throw InputMismatchException if the next token cannot be translated into a valid float value as described below. If the translation is successful, the scanner advances past the input that matched.
• public Scanner useDelimiter(String pattern) – Sets this scanner’s delimiting pattern to a pattern constructed from the specified String. An invocation of this method of the form useDelimiter(pattern) behaves in exactly the same way as the invocation useDelimiter(Pattern.compile(pattern)). Invoking the reset() method will set the scanner’s delimiter to the default.

If we run the above code, we will get the following results:

6. Not so common use of java.util.Scanner class

The java.util.Scanner provides a single API for not only parsing indi‐ vidual primitive types from strings, but reading them from a stream of tokens.

The Scanner API is smarter and can use Locales to parse numbers in specific languages with more elaborate conventions. You can specify a Locale other than the default with the useLocale() method.

JavaNetURLMoreMethodsExample.java

Let’s explain the methods used in the above example.

• public byte nextByte() – Scans the next token of the Java input as a byte.
• public long nextLong() – Scans the next token of the Java input as a long.
• public Scanner useLocale(Locale locale) – Sets this scanner’s locale to the specified locale. A scanner’s locale affects many elements of its default primitive matching regular expressions; see localized numbers above. Invoking the reset() method will set the scanner’s locale to the initial locale.

If we run the above code, we will get the following results:

7. More articles

• Java String Class Example
• String CompareTo Java Example

8. Download the source code

That was an example about the java.util.Scanner class. We also saw how to use this class to read a Java input form the console.

Last updated on Apr. 27th, 2021

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