OCPJP Simulation Test 70

70

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

Choice:
A. queue.add(new ObjectStreamReader());
B. queue.add(new InputStreamReader());
C. queue.add(new Reader());
D. queue.add(new FileInputStream());
E. queue.add(new ObjectInputStreamReader());
F. queue.add(new BufferedReader());
G. queue.add(new FileReader());
H. queue.add(new BufferedInputStream());



Next Question

Answer: B, G

Explain: regardless of the right side assignment, only the left side type declaration counts: Queue<? super InputStreamReader> queue  You can only add the subclass of InputStreamReader 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.