EXCEPTION HANDLING AND TEXT I/O - Introduction to Java Programming: Comprehensive Version - page 478

A resource is declared and created followed by the keyword try . Note that the resources are
enclosed in the parentheses (lines 9-12). The resources must be a subtype of AutoCloseable
such as a PrinterWriter that has the close() method. A resource must be declared and
created in the same statement and multiple resources can be declared and created inside the
parentheses. The statements in the block (lines 12-18) immediately following the resource
declaration use the resource. After the block is finished, the resource's close() method
is automatically invoked to close the resource. Using try-with-resources can not only avoid
errors but also make the code simpler.

12.11.3 Reading Data Using Scanner
The java.util.Scanner class was used to read strings and primitive values from the con-
sole in Section 2.3, Reading Input from the Console. A Scanner breaks its input into tokens
delimited by whitespace characters. To read from the keyboard, you create a Scanner for
System.in , as follows:

Scanner input = new Scanner(System.in);

To read from a file, create a Scanner for a file, as follows:

Scanner input = new Scanner( new File(filename));

Figure 12.9 summarizes frequently used methods in Scanner .

java.util.Scanner

+Scanner(source: File)
+Scanner(source: String)
+close()
+hasNext(): boolean
+next(): String
+nextLine(): String
+nextByte(): byte
+nextShort(): short
+nextInt(): int
+nextLong(): long
+nextFloat(): float
+nextDouble(): double
+useDelimiter(pattern: String):
Scanner

Creates a Scanner that scans tokens from the specified file.
Creates a Scanner that scans tokens from the specified string.
Closes this scanner.
Returns true if this scanner has more data to be read.
Returns next token as a string from this scanner.
Returns a line ending with the line separator from this scanner.
Returns next token as a byte from this scanner.
Returns next token as a short from this scanner.
Returns next token as an int from this scanner.
Returns next token as a long from this scanner.
Returns next token as a float from this scanner.
Returns next token as a double from this scanner.
Sets this scanner's delimiting pattern and returns this scanner.

F IGURE 12.9

The Scanner class contains the methods for scanning data.

Listing 12.15 gives an example that creates an instance of Scanner and reads data from
the file scores.txt .

L ISTING 12.15

ReadData.java

1 import java.util.Scanner;
2
3 public class ReadData {
4 public static void main(String[] args) throws Exception {
5 // Create a File instance
6 java.io.File file = new java.io.File( "scores.txt" );
7
8 // Create a Scanner for the file
9 Scanner input = new Scanner(file);

create a File

create a Scanner