OCPJP Simulation Test 76

76

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Question: Given Queue<? super InputStream> queue = new LinkedBlockingQueue<InputStream>(), what are the following code compiles?

Choice:
A. queue.add(new InputStream());
B. queue.add(new FilePrintStream());
C. queue.add(new PrintInputStream());
D. queue.add(new BufferedInputStream());
E. queue.add(new ObjectInputStream());
F. queue.add(new OutputStream());
G. queue.add(new FilteredInputStream());
H. queue.add(new printStream());



Next Question

Answer: D, E

Explain: regardless of the right side assignment, only the left side type declaration counts: Queue<? super InputStream> queue.  You can only add the subclass of InputStream to the queue. Of course you need to be familiar with NIO classes. We didn't choose A because InputStream is an abstract class.

Study:  Create and use a generic class 
Use BufferedReader, BufferedWriter, File, FileReader, FileWriter, FileInputStream, FileOutputStream, ObjectOutputStream, ObjectInputStream, and PrintWriter in the java.iopackage.