The Scanner class, introduced with J2SE 5.0, is a very useful new class that can parse text for primitive types and substrings using regular expressions. It can obtain the text from sources such as a String object, an InputStream, a File, and any class that implements the Readable interface.

The Scanner splits input into substrings, or tokens, separated by delimiters, which by default consist of any white space. The tokens can then be obtained as strings or as primitive types if that is what they represent.

For example, the following code snippet shows how to read an integer from the keyboard

For each of the primitive types there is a corresponding nextXxx() method that returns a value of that type. If the string cannot be interpreted as that type, then an InputMismatchException is thrown.

There is also a set of hasNextXxx() methods, such as hasNextInt(), that return true or false according to whether the next token matches the specified type.

The program ScanConsoleApp demonstrates how to read int, float, and double values from the keyboard.

A session with this program goes as follows:

There are a number of other useful methods in the Scanner class such as skip() to jump over input, useDelimiter() defines a delimiter in place of the default white space, and findInLine() to search for substrings.

The Scanner class uses tools from the java.util.regex package, which deals with pattern matching using regular expressions. We don't have space here to describe these very powerful text matching tools but you can find more info in the Java 2 API Specifications.

References and Web Resources

• java.util.Scanner - class specifications for J2SE5.0. Example codes are included in the introduction.
• Readable interface
• java.util.regex package