Java Reference
In-Depth Information
Display 10.20
File I/O of an Array Object
(part 3 of 3)
56
for
(i = 0; i < b.length; i++)
57 System.out.println(b[i]);
58 System.out.println("End of program.");
59 }
60 }
Sample Dialogue
Array written to file arrayfile.
Now let's reopen the file and display the array.
The following array elements were read from the file:
Number = 1 Letter = A
Number = 2 Letter = B
End of program.
10.5
Random Access to Binary Files
★
Anytime, anywhere.
Common response to a challenge for a confrontation
The streams for sequential access to files, which we discussed in the previous sections
of this chapter, are the ones most often used for file access in Java. However, some
applications that require very rapid access to records in very large databases require
some sort of random access to particular parts of a file. Such applications might best be
done with specialized database software. But perhaps you are given the job of writing
such a package in Java, or perhaps you are just curious about how such things are done
in Java. Java does provide for random access to files so that your program can both read
from and write to random locations in a file. In this section, we will describe simple
uses of random access to files.
Reading and Writing to the Same File
If you want random access to both read and write to a file in Java, use the stream class
RandomAccessFile
, which is in the
java.io
package like all other file I/O classes.
A random access file consists of a sequence of numbered bytes. There is a kind of
marker called the
file pointer
that is always positioned at one of these bytes. All reads
and writes take place starting at the location of the file pointer. You can move the file
pointer to a new location with the method
seek
.
Although a random access file is byte oriented, there are methods to allow for
reading or writing values of the primitive types and of string values to a random access
file. In fact, these are the same methods as those we already used for sequential access
files, as previously discussed. A
RandomAccessFile
stream has methods
writeInt
,
writeDouble
,
writeUTF
, and so forth, as well as methods
readInt
,
readDouble
,
file pointer
