File I/O - Java - page 565

Self-Test Exercises
28. How do you open the binary file bindata.dat so that it is connected to an out-
put stream of type ObjectOutputStream that is named outputThisWay ?
29. Give two statements that will write the values of the two double variables v1 and
v2 to the file bindata.dat . Use the stream outputThisWay that you created as
the answer to Self-Test Exercise 28.
30. Give a statement that will write the string value "Hello" to the file bindata.dat .
Use the stream outputThisWay that you created as the answer to Self-Test
Exercise 28.
31. Give a statement that will close the stream outputThisWay created as the answer
to Self-Test Exercise 28.

then you can read that number back with the method readDouble of ObjectInput-
Stream , and so forth. Display 10.16 gives an example of using readInt in this way.

Display 10.15 Some Methods in the Class ObjectInputStream (part 1 of 3)

The classes ObjectInputStream and FileInputStream are in the java.io package.

public ObjectInputStream(InputStream streamObject)

There is no constructor that takes a file name as an argument. If you want to create a stream using a
file name, you use
new ObjectInputStream( new FileInputStream( File_Name ))
Alternatively, you can use an object of the class File in place of the File_Name , as follows:
new ObjectInputStream( new FileInputStream( File_Object ))
The constructor for FileInputStream may throw a FileNotFoundException , which is a kind of
IOException . If the FileInputStream constructor succeeds, then the constructor for ObjectIn-
putStream may throw a different IOException .

public int readInt() throws IOException

Reads an int value from the input stream and returns that int value. If readInt tries to read a value
from the file and that value was not written using the method writeInt of the class ObjectOutput-
Stream (or written in some equivalent way), then problems will occur. If an attempt is made to read
beyond the end of the file, an EOFException is thrown.

public int readShort() throws IOException

Reads a short value from the input stream and returns that short value. If readShort tries to read
a value from the file and that value was not written using the method writeShort of the class
ObjectOutputStream (or written in some equivalent way), then problems will occur. If an attempt is
made to read beyond the end of the file, an EOFException is thrown.

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