SCJP Exam 1.4

Author: Razvan MIHAIU
razvan_rem@rem_mihaiu.name (please remove '_rem' and 'rem_')
From: www.mihaiu.name
Date: 25/10/2004

Page 1: SCJP questions 1-20

Page 2: SCJP questions 21-40

Page 3: SCJP questions 41-53

  1. What is the output of the following program ?

    public class CDummy { static int unu = 1; public static void main(String args[]) { System.out.println("CDummy."); CDummy cd = new CDummy(); System.out.println(cd.unu); System.out.println(unu); System.out.println(CDummy.unu); } }

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    Dummy. 1 1 1
  2. What is wrong with the following code ? (there is a logical not syntactical error)
    public void coolFunction() { String tmp; synchronized(tmp) { doSyncWork(); } }

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    The synchronization takes place on a local variable. This is useless because all threads have their local copy of a local variable. As it is the code is not synchronized at all.

  3. What is the output of the following code ?
    try { System.out.println("Test !"); } catch(InterruptedException ee) { System.out.println("The main thread was interrupted !"); }

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    The code does not compile because the exception InterruptedException is never thrown. (InterruptedException is checked)

  4. What is the output of the following code ?
    try { System.out.println("Test !"); } catch(IndexOutOfBoundsException ee) { System.out.println("The main thread was interrupted !"); }

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    Test !

    Attention: IndexOutOfBoundsException is not checked (for this reason the code compiles)

  5. Can you attach many threads to a class extending Thread ? True/False.

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    Answer: True.

    This is a tricky question. Bear in mind that the class Thread implements the Runnable interface. As a result you could always write something like this:

    class MyThread extends Thread{} MyThread th = new MyThread(); new Thread(th).start(); new Thread(th).start(); new Thread(th).start();

    Thus to the object "th" you can attach many threads.

    OTOH it is true that you cannot call many times the start() method on the same object:

    th.start(); th.start();
    because the code will fail at runtime.

  6. Can you attach many threads to a class implementing Runnable ? True/False.

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    Answer: True

  7. Will the following code compile ? Yes/No
    class CDummy { int someInt; void printData(String input) { synchronized (someInt) { System.out.println(input); } } }

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    No ! Synchronization can only be done on Object(s) not primitives.

  8. When an IllegalMonitorStateException is thrown ?

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    When the wait() or notify() functions are called on an Object on which the current thread does not have a lock.

  9. Does the following code compile ? Yes/No
    public class CDummy { static int someVar1 = 9; int someVar2 = 11; public static void main(String args[]) { System.out.println("CDummy."); NestedTwo ns2 = new CDummy().new NestedTwo(); System.out.println(ns2.getOuterVariable2()); } class NestedTwo { static int getOuterVariable1() {return someVar1;} int getOuterVariable2() {return someVar2;} } }

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    No. Inner classes cannot have static attributes or members. The function getOuterVariable1() is static.

  10. What are nested classes ?

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    Any class defined inside another class.

  11. What are inner classes ?

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    Non-static nested classes.

  12. How many types of nested classes there are ?

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    Static nested classes and inner classes.

  13. How can you define a static inner class ?

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    Inner classes are not static by definition, nor do they allow any static member functions or attributes.










Best regards,
Razvan MIHAIU




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