Quiz 1

1
Quiz 1

• Quiz 1
• What is this? (explain the use of the reserved
  word this in a class method).
• Answer each question briefly.
• What is a Constructor?
• Under what circumstances would a Constructor
  method for a class execute?
• Can a class have more than one Constructor?
• Given
• String s "potato"
• String v s.substring(0,3)
• String w s.substring(0,3)
• Is vw true or false?

• This is an object reference that refers to the
  current object for which a method was invoked.
• Brief answers
• A method invoked on object creation.
• Typically, a Constructor is executed when an
  object is created by use of the new operator.
• Yes, as long as they have different parameters.
• v w is false. The substring method will create
  new objects each time it is invoked.

2
Quiz 2

• The following code creates a 2x2 block of
  buttons. Add/modify the code to create an applet
  with 6 buttons arranged in 3 rows and 2 columns..
• import javax.swing.
• import java.awt.
• public class ButtonJComponent extends JApplet
• public void init()
• Container c getContentPane()
• c.setLayout(new GridLayout(2,2)
• JButton button1 new JButton("one")
• JButton button2 new JButton("two")
• JButton button3 new JButton("three")
• JButton button4 new JButton("four")
• 2. Discuss the changes necessary to make the
  program in 1 a stand-alone java app instead of an
  applet.
• You may discuss this in wordsexact code is not
  necessary in all cases, but try to cover all the
  steps.
• For example

• Change body to
• c.setLayout(new GridLayout(3,2)
• JButton button1 new JButton("one")
• JButton button2 new JButton("two")
• JButton button3 new JButton("three")
• JButton button4 new JButton("four")
• JButton button3 new JButton("five")
• JButton button4 new JButton("six")
• The following two lines are sufficient
• for(int i0 i lt b.length i)
• System.out.println(bi)
• -extends JApplet changes to extends JFrame

3
Quiz 3-1

• 1. What error will Java report from the
  following code? (That iswhats wrong with this
  sequence? You do not need the actual error
  message.)
• int a
• a3 5
• 2. Correct any errors in the following
  declaration.
• char vowel a, e, i, o, u
• 3. Consider
• int v 23, 44,
  78
• int w v
• w2 100
• What is the value of v2?
• 4. Write Java code to swap integer array
  elements ai and aj.

• a is a reference to an array, but the array has
  not been created (with the new operator for
  instance). The actual error reported is
  variable a might not have been initialized
• char vowel a,b,c,d,e
• v2 has the value of 100. (w is an alias of v so
  the statement w2 100 also changes v.
• Something like this
• int I,J,temp
• temp aI
• aI aJ
• aI temp

4
Quiz 4

• Show the contents of a stack (of Strings) after
  the every 5 operations and at the end.Assume the
  stack is initially empty. Display the stack from
  Top to bottom. (Commands are listed left to right
  to conserve space.
• Push (Example)
• Push (Bogus)
• Push (Sham)
• Pop()
• Pop()
• Push(Fine)
• Push(A)
• Push(Of)
• Pop()
• Push(Heck)
• Push(One)
• Pop()
• Pop()
• Push(Is)
• Push(List)
• Pop()
• Push(This)

• At the end the stack will have (from top to
  bottom)
• This
• Is
• A
• Fine
• Example
• The list of operations is intended to be one
  continuous list, with line breaks. So the final
  answer is (from left to right)
• it is a Fine Example Anyway

5
Quiz 5

• Which of the following correctly describes the
  relation between an abstract class and an
  interface?
• An interface is another name for an abstract
  class.
• An interface is not a class, but is otherwise
  identical to an abstract class.
• Every abstract class implements an interface.
• An abstract class must be totally abstract, but
  an interface may be partially implemented.
• None of the above
• The code
• public class B extends A
• defines a class that inherits all the methods of
  A
• defines a class that inherits the public methods
  of A only
• will not compile because the body in empty
• none of the above
• The code
• public class B extends A
• defines a class B that
• implements A
• is a superclass of A
• is a subclass of A

• None of the above. All of the statements are
  false.
• None of the above. B inherits public and
  protected methods and if they are in the same
  package, B will inherit methods created with no
  modifier.
• B is a subclass of A

6

• Quiz 6
• What is displayed on the console when the
  following code is run?
• class Test
• public static void main(String args)
• try
• System.out.println("Welcome to Java")
• int i0
• int y2/i
• System.out.println("Exceptions are fun")
• catch(RuntimeException ex)
• System.out.println("I take Exception to
  that")
• finally