OCPJP Simulation Test 71

71

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Question: Given Deque<? super FilterOutputStream> deque = new ArrayDeque<OutputStream>(), what are the following code compiles?

Choice:
A. deque.add(new Object());
B. deque.add(new OutputStream());
C. deque.add(new FilterOutputStream());
D. deque.add(new BufferOutputStream());
E. deque.add(new ObjectInputStream());
F. deque.add(new PrintStream());
G. deque.add(new ObjectOutputStream());
H. deque.add(new printerWriter());



Next Question

Answer: C, F

Explain: regardless of the right side assignment, only the left side type declaration counts: Deque<? super FilterOutputStream> queue  You can only add the subclass of FilterOutputStream to the queue. Of course you need to be familiar with NIO classes.

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