OCPJP Simulation Test 69

69

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Question: Given Queue<? super OutputStream> queue = new ArrayBlockingQueue<OutputStream>(10), what are the following code compiles?

Choice:
A. queue.add(new OutputStream());
B. queue.add(new FileOutputStream());
C. queue.add(new FileWriter());
D. queue.add(new BufferedOutputStream());
E. queue.add(new ObjectOutputStream());
F. queue.add(new BufferedWriter());
G. queue.add(new FilterInputStream());
H. queue.add(new PrintStream());



Next Question

Answer: B, D, E, G, H

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