06. Scanner

Scanner

ND079 C1 L4 A06 Scanner

The Scanner class can read and parse simple text. Here are some key points to keep in mind:

  • It parses primitive types and String types into tokens.
  • By default it uses whitespaces to delimitate each word. However, it can also use regular expressions.
  • The Scanner class can read from several different types of sources, like strings, files and System.in (to get input from the command line).

Scanner Syntax

Example 1

We can use the Scanner class to get input from the command line. To do so, we instantiate a scanner object, passing in System.in:

Scanner scanner = new Scanner(System.in);

Example 2

In this example we are using the nextLine method to return the full line of the input:

Scanner scanner = new Scanner("This is a line");
System.out.println(scanner.nextLine());

Output:

This is a line

Example 3

In this next example, we are using the next method to read the first token. The next method finds and returns the next complete token.

Scanner scanner = new Scanner("This is a line");
System.out.println(scanner.next());

Output:

This

Example 4

In the final example, we are using the hasNext() method in a while loop to determine if it is safe to call the next method. We only want to call the next method when we know there is a token available.

Note: By default the Scanner tokenizes input by whitespaces. Let's say we have a string with the following text "One Two Three". The text will be tokenized into three separate tokens, "One", "Two" and "Three".

Scanner scanner = new Scanner("This is a line");

while(scanner.hasNext()) {
    System.out.println(scanner.next());
}

**Output: ** 

This
is
a
line

Which of the following statements are true about the Scanner class?

(Select all that apply.)
SOLUTION:
  • The Scanner class can be used to read input from the console.
  • The Scanner class can also use RegEx to parse console input.

QUIZ QUESTION::

Match the code with the correct output for the String "1 number";

ANSWER CHOICES:



Code

Output

 
scanner.nextLine()
 
scanner.next()
 
while(scanner.hasNext()) {
  System.out.println(scanner.next());
}
 
scanner.nextInt()
SOLUTION:

Code

Output

 
scanner.next()
 
scanner.nextInt()
 
scanner.next()
 
scanner.nextInt()
 
while(scanner.hasNext()) {
  System.out.println(scanner.next());
}
 
scanner.nextLine()

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