I PRepared by using "Complete java 2 Certification Study Guide" for Simon Roberts (Sybex). 1. public class x implements Runnable{ private int x; private int y;
public static void main(String args[] ){ x that = new x(); (new Thread(that)).start(); (new Thread(that)).start(); } public synchronized void run(){ for( ; ; ){ x++; y++; System.out.Println("x=" + x + ", y=" +y); } }
a. An error at line 11 b. An error at line 7, 8 c. The program prints pairs of values for x and y that might not always be the same on the same line (for example "x=2, y=1") d. The program prints pairs of values for x and y that are always the same on the same line (for example "x=1, y=1") in addition, each value appears twice (for example "x=1, y=1" followed by "x=1, y=1") e. The program prints pairs of values for x and y that are always the same on the same line (for example "x=1, y=1") in addition, each value appears only once (for example "x=1, y=1", followed by "x=2, y=2)
Answer: E (my; C)
2. 1. public class x{ 2. public object m(){ 3. Object o=new Float(2.14F); 4. Object [] oa=new Object[1]; 5. oa[0]=o; 6. o=null; 7. return o; 8. } // end m() method. 9. }
When is the Float object creation in line 3 eligible for garbage collection ?
a. just after line 5 b. just after line 6 c. just after line 7 (that is , as the method returns) d. just after line 8 (that is, as the method ends)
Answer: I choose d which was wrong. I think ; b
3. 1. abstract class AbstractIt{ 2. abstract float getFloat(); 3. } 4. public class AbstractTest extends AbstractIt{ 5. private float f1 = 1.0f; 6. private float getFloat(){return f1} 7. }
what result?
a. compile sUCcess b. An error at line 6 c. An error at line 4 d. An error at line 2
Answer: b getFloat() in AbstractTest cannot override getFloat() in AbstractIt; attempting to assign weaker access privileges; was package
4. import java.io.IOException;
public class ExceptionTest{ public static void main(String[] args){ try{ methodA(); }catch(IOException io){ System.out.println("caught IOException"); }catch(Exception e){ System.out.println("caught Exception"); } } public void methodA(){ throw new IOException(); } }
what result?
a. The code will not compile b. Output is "caught Exception" c. Output is "caught IOException" d. The program execute nomally whihout print a message
Answer: a non-static method methodA() cannot be refereced from a static context.
5. public class Foo{ public static void main(String[] args)[ try{ return;} finally{ System.out.println("Finally");} ] }
what result?
a. Print nothing b. Print "Finally" c. Not compiled and will Exception thrown d. Not compile because catch block missing
Answer: b
6. public class Foo{ public static void main(String[] args){ StringBuffer a = new StringBuffer("A"); StringBuffer b = new StringBuffer("B"); Operate(a,b); System.out.println(a + "," + b); } static void operate(StringBuffer x,StringBuffer y){ y.append(x); y = x; } // end operate }
What print?
a. "A,B" b. "A,A" c. "B,B" d. "AB,B" e. "AB,AB" f, "A,AB"
Answer: F ans: A,BA
7. 1. class A implements Runnable { 2. int I; 3. public void run () { 4. try { 5. Thread.sleep(5000); 6. i=10; 7. }catch(InterruptedException e) {} 8. } 9. } 10. 11. public class Test { 12. public static void main (String args[]) { 13. try { 14. A a = new A(); 15. Thread t = new Thread(a); 16. t.start(); 17. 18. int j= a.i; 19. 20. }catch (Exception e) {} 21. } 22. }
Which statement at line 17 will ensure that j=10 at line 19
A. a.wait(); B. t.wait(); C. t.join(); D. t.yield(); E. t.notify(); F. a.notify(); G. t.interrupt();
Answer: C
8. 1. public class SyncTest { 2. private int x; 3. private int y; 4. private synchronized void set X (int i){ x=i; } 5. private synchronized void set Y (int i){ y=i; } 6. public void setXY (int i) {set X(i); set Y(i); } 7. public synchronized boolean check() {return X != Y; } 8. }
Under which conditions will check() return when called from a different class. Choose one
A. check() can never return true B. check() can return true when set XY is called by multiple threads C. check() can true when multiple threads call set X and set Y separately D. check() can only return true if synchTest is changed to allow x and y to be set separately
Answer: I choose D
9. Which is a method of the MouseMotionListener interface
A. public void mouseDragged(MouseEvent) B. public boolean mouseDragged(MouseEvent) C. public void mouseDragged(MouseMotionEvent) D. public boolean mouseDragged(MouseMotionEvent) E. public boolean mouseDragged(MouseMotionEvent)
Answer: A
10. AnInterface is an interface. AnAdapter0 is an non-Abstract, not-final with zero argument construter AnAdapter1 is an non-Abstract, not-final without zero argument construter, but with a constructor to take one argument.
Which will create Anonymous class (choose two)
a}AnAdapter0 a = new AnAdapter0(); b}AnAdapter1 a = new AnAdapter1(); c}AnAdapter0 a = new AnAdapter0(5); d}AnAdapter1 a = new AnAdapter1(5); e}AnInterface a = new AnInterface(5);
Ans: a and d are correct. B, c and e are wrong.
11. What is true about java.util.Arraylist (choose one)
a)The elements in the collection are ordered b)The collection is guaranteed to be immutable. c)The elements in the collection are guaranteed to be unique. d)The elements in the collection are accessed using a unique key e)The elements in the collection are guaranteed to be synchronized
Answer: A is correct. ArrayList implemnets all optional List operation. b is wrong because lists typically allow duplicate elements. C is wrong this is Set facility. D is wrong because this is Map facility. E is wrong, Note that this implementation is not synchronized. If multiple threads access an ArrayList instance concurrently, and at least one of the threads modifies the list structurally, it must be synchronized externally ( refer documents )
12. 1.class A{ 2. public int getNumber(int a){ 3. return a +1; 4. } 5.} 6.class B extends A{ 7. public int getNumber(int a){ 8. return a + 2; 9. } 10. public static void main(String args[]){ 11. B b = new B();
