Random file access in Java

Objectives

• use binary file I/O in Java

Binary file I/O

• Need to use: import java.io.*;
• Remember to catch exceptions on all file I/O operations or specify that the enclosing method throws that exception.
• We have two good choices for dealing with binary files easily:
  • open a FileInputStream or FileOutputStream and wrap it in a DataInputStream or DataOutputStream - good for sequential access binary data
  • open a RandomAccessFile - this is good when you want to jump around a file or read and write a file - it implements DataInput and DataOutput (like DataInputStream and DataOutputStream do)
• See the Java API documentation for DataInputStream, DataOutputStream, and RandomAccessFile
• The DataInput interface declares methods for reading the basic data types, such as readInt(), readDouble(), and readBoolean(). It also declares the method readLine() to read a whole line of input at once.
• The DataOutput interface declares methods for writing the basic data types, such as writeInt(), writeDouble(), and writeBoolean(). It also declares the method writeChars() to send a String to output.
• Remember to close (close() method) files when you are done using them.
• See Binary01.java: writes and then reads binary data in a file
• See Binary02.java: writes and then reads binary data in a file using a class for the record to make life easier
• See CreateData02.java: program used to create binary data file from a text file with population data
• See RandomTest.java: demonstrates random access file techniques
• See RandomTest2.java: variation of RandomTest.java that converts Unicode characters to byte values to save space