Deck 10: Interfaces

Question 1

____ methods must be implemented when using an interface.

A) Abstract.
B) Private.
C) Public.
D) Static

Answer 1

A

Question 2

Consider the following code snippet: public class Inventory implements Measurable
{
) . .
Double getMeasure();
{
Return onHandCount;
}
}
The compiler complains that the getMeasure method has a weaker access level than the Measurable interface. Why?

A) All of the methods in a class have a default access level of package access, while the methods of an interface have a default access level of private.
B) All of the methods in a class have a default access level of package access, while the methods of an interface have a default access level of public.
C) The variable onHandCount was not declared with public access.
D) The getMeasure method was declared as private in the Measurable interface.

Answer 2

B

Question 3

Which of the following statements about interfaces is NOT true?

A) Interfaces can make code more reusable.
B) An interface provides no implementation.
C) A class can implement only one interface type.
D) Interfaces can reduce the coupling between classes.

Answer 3

C

Question 4

Which of the following statements about a Java interface is NOT true?

A) A Java interface defines a set of methods that are required.
B) A Java interface must contain more than one method.
C) A Java interface specifies behavior that a class will implement.
D) All methods in a Java interface must be abstract.

Question 5

Which of the following statements about an interface is true?

A) An interface has methods and instance variables.
B) An interface has methods but no instance variables.
C) An interface has neither methods nor instance variables.
D) An interface has both public and private methods.

Question 6

Consider the following code snippet. public interface Measurable
{
Double getMeasure();
}
Public class Coin implements Measurable
{
Public double getMeasure()
{
Return value;
}
)..
}
Public class DataSet
{
)..
Public void add()
{
)..
}
}
Public class BankAccount
{
)..
Public void add()
{
)..
}
}
Which of the following statements is correct?

A) Coin dime = new Coin(0.1, "dime");
Measurable x = dime;
B) Coin dime = new Coin(0.1, "dime");
Dataset x = dime;
C) Coin dime = new Coin(0.1, "dime");
DataSet x == (Measureable)dime;
D) Coin dime = new Coin(0.1, "dime");
BankAccount x = dime;

Question 7

Consider the following code snippet: public class Inventory implements Measurable
{
) . .
Double getMeasure();
{
Return onHandCount;
}
}
What is wrong with this code?

A) The getMeasure() method must be declared as private.
B) The getMeasure() method must include the implements keyword.
C) The getMeasure() method must be declared as public.
D) The getMeasure() method must not have any code within it.

Question 8

Consider the following code snippet: public class Inventory implements Measurable
{
) . .
Public double getMeasure();
{
Return onHandCount;
}
}
Why is it necessary to declare getMeasure as public ?

A) All methods in a class are not public by default.
B) All methods in an interface are private by default.
C) It is necessary only to allow other classes to use this method.
D) It is not necessary to declare this method as public.

Question 9

Which of the following statements about abstract methods is true?

A) An abstract method has a name, parameters, and a return type, but no code in the body of the method.
B) An abstract method has parameters, a return type, and code in its body, but has no defined name.
C) An abstract method has a name, a return type, and code in its body, but has no parameters.
D) An abstract method has only a name and a return type, but no parameters or code in its body.

Question 10

Consider the following declarations: public interface Encryptable
{
Void encrypt(String key);
}
Public class SecretText implements Encryptable
{
Private String text;
_____________________________
{
// code to encrypt the text using encryption key goes here
}
}
Which of the following method headers should be used to complete the SecretText class?

A) public void encrypt()
B) public void encrypt(String aKey)
C) public String encrypt(String aKey)
D) void encrypt(String aKey)

Question 11

To use an interface, a class header should include which of the following?

A) The keyword extends and the name of an abstract method in the interface
B) The keyword extends and the name of the interface
C) The keyword implements and the name of an abstract method in the interface
D) The keyword implements and the name of the interface

Question 12

____ can reduce the coupling between classes.

A) Static methods
B) Abstract methods
C) Interfaces
D) Objects

Question 13

Which statement about methods in an interface is true?

A) All methods in an interface are automatically private.
B) All methods in an interface are automatically public.
C) All methods in an interface are automatically static.
D) All methods in an interface must be explicitly declared as private or public.

Question 14

Suppose you are writing an interface called Resizable, which includes one void method called resize. public interface Resizable
{
_________________________
}
Which of the following can be used to complete the interface declaration correctly?

A) private void resize();
B) protected void resize();
C) void resize();
D) public void resize() { System.out.println("resizing ..."); }

Question 15

Which of the following statements about converting between types is true?

A) When you cast number types, you take a risk that an exception will occur.
B) When you cast number types, you will not lose information.
C) When you cast object types, you take a risk of losing information.
D) When you cast object types, you take a risk that an exception will occur.

Question 16

Which of the following statements about interfaces is true?

A) You can define an interface variable that refers to an object of any class in the same package.
B) You cannot define a variable whose type is an interface.
C) You can instantiate an object from an interface class.
D) You can define an interface variable that refers to an object only if the object belongs to a class that implements the interface.

Question 17

A method that has no implementation is called a/an ____ method.

A) interface
B) implementation
C) overloaded
D) abstract

Question 18

Which of the following statements about interfaces is NOT true?

A) Interfaces can make code more reusable.
B) Interface types can be used to define a new reference data type.
C) Interface types can be used to express common operations required by a service.
D) Interfaces have both private and public methods.

Question 19

Consider the following code snippet: public interface Sizable
{
Int LARGE_CHANGE = 100;
Int SMALL_CHANGE = 20;
Void changeSize();
}
Which of the following statements is true?

A) LARGE_CHANGE and SMALL_CHANGE are automatically public static final.
B) LARGE_CHANGE and SMALL_CHANGE are instance variables
C) LARGE_CHANGE and SMALL_CHANGE must be defined with the keywords private static final.
D) LARGE_CHANGE and SMALL_CHANGE must be defined with the keywords public static final.

Question 20

Which of the following is true regarding a class and interface types?

A) You can convert from a class type to any interface type that is in the same package as the class.
B) You can convert from a class type to any interface type that the class implements.
C) You can convert from a class type to any interface type that the class defines.
D) You cannot convert from a class type to any interface type.

Question 21

In Java, ____ can be used for callbacks.

A) Objects
B) Interfaces
C) Classes
D) Operators

Question 22

If you have multiple classes in your program that have implemented the same interface in different ways, how is the correct method executed?

A) The Java virtual machine must locate the correct method by looking at the class of the actual object.
B) The compiler must determine which method implementation to use.
C) The method must be qualified with the class name to determine the correct method.
D) You cannot have multiple classes in the same program with different implementations of the same interface.

Question 23

Which of the following statements about an inner class is true?

A) An inner class that is defined inside a method is publicly accessible.
B) An inner class that is defined inside a method is not publicly accessible.
C) An inner class that is defined inside an enclosing class but outside of its methods is not available to all methods of the enclosing class.
D) An inner class is used for a utility class that should be visible elsewhere in the program.

Question 24

The method below is designed to print the smaller of two values received as arguments. Select the correct expression to complete the method. public void showSmaller(Comparable value1, Comparable value2)
{
If ( _________________________ )
System.out.println(value1 + " is smaller.");
Else
System.out.println(value2 + " is smaller.");
}

A) value1 < value2
B) value1.compareTo(value2) > 0
C) value1.compareTo(value2) == 0
D) value1.compareTo(value2) < 0

Question 25

Assuming that interface Resizable is declared elsewhere, consider the following class declaration: public class InnerClassExample
{
Public static void main(String[] args)
{
Class SizeModifier implements Resizable
{
// class methods
}
__________________________ // missing statement
}
}
Which of the following declarations can be used to complete the main method?

A) Resizable something = new Resizable();
B) Resizable something = new SizeModifier();
C) Resizable something = new InnerClassExample();
D) SizeModifier something = new Resizable();

Question 26

Which of the following statements about a callback is NOT true?

A) A callback can allow you to implement a new method for a class that is not under your control.
B) A callback can be implemented using an interface.
C) A callback is a mechanism for specifying code to be executed later.
D) A callback method declared in an interface must specify the class of objects that it will manipulate.

Question 27

Which of the following is a good use for an anonymous class?

A) Use an anonymous class to implement polymorphism.
B) Use an anonymous class to implement a callback.
C) Use an anonymous class when all methods of the class will be static methods.
D) Use an anonymous class when the program will only need one object of the class.

Question 28

Which of the following statements about an inner class is true?

A) An inner class can only be defined within a specific method of its enclosing class.
B) An inner class can only be defined outside of any method within its enclosing class.
C) An inner class must implement an interface.
D) An inner class may be anonymous.

Question 29

You wish to implement a callback method for an object created from a system class that you cannot change. What approach does the textbook recommend to accomplish this?

A) Create a new class that mimics the system class.
B) Extend the system class.
C) Use an inner class in the interface.
D) Use a helper class that implements the callback method.

Question 30

____ occurs when a single class has several methods with the same name but different parameter types.

A) Casting
B) Polymorphism
C) Overloading
D) Instantiation

Question 31

Consider the following declarations: public interface Displayable
{
Void display();
}
Public class Picture implements Displayable
{
Private int size;
Public void increaseSize()
{
Size++;
}
Public void decreaseSize()
{
Size--;
}
Public void display()
{
System.out.println(size);
}
Public void display(int value)
{
System.out.println(value * size);
}
}
What method invocation can be used to complete the code segment below?
Displayable picture = new Picture();
Picture._________________;

A) increaseSize()
B) decreaseSize()
C) display()
D) display(5)

Question 32

Consider the following code snippet: myImage.add(new Rectangle(10,10,10,10));
This code is an example of using ____.

A) An anonymous class.
B) An anonymous object.
C) An abstract object.
D) An abstract class.

Question 33

You have created a class named Motor that implements an interface named Measurable. You have declared a variable of type Measureable named motorTemperature. Which of the following statements is true?

A) The object to which motorTemperature refers has type Measurable.
B) The object to which motorTemperature refers has type Motor.
C) This declaration is illegal.
D) You must construct a motorTemperature object from the Measurable interface.

Question 34

Which of the following can potentially be changed when implementing an interface?

A) The parameters of a method in the interface.
B) The name of a method in the interface.
C) The return type of a method in the interface.
D) You cannot change the name, return type, or parameters of a method in the interface.

Question 35

Which of the following statements about a mock class is true?

A) A mock class does not provide an implementation of the services of the actual class.
B) A mock class provides a complete implementation of the services of the actual class.
C) A mock class provides a simplified implementation of the services of the actual class.
D) A mock class must be an interface.

Question 36

A/an ____ class defined in a method signals to the reader of your program that the class is not interesting beyond the scope of the method.

A) A class cannot be defined within a method
B) abstract
C) interface
D) inner

Question 37

Consider the following code snippet: public class Demo
{
Public static void main(String[] args)
{
Point[] p = new Point[4];
P[0] = new Colored3DPoint(4, 4, 4, Color.BLACK);
P[1] = new ThreeDimensionalPoint(2, 2, 2);
P[2] = new ColoredPoint(3, 3, Color.RED);
P[3] = new Point(4, 4);
For (int i = 0; i < p.length; i++)
{
String s = p[i].toString();
System.out.println("p[" + i + "] : " + s);
}
Return;
}
}
This code is an example of ____.

A) overloading
B) callback
C) early binding
D) polymorphism

Question 38

Consider the following declarations: public interface Measurer
{
Int measure(Object anObject);
}
Public class StringLengthMeasurer implements Measurer
{
Public int measure(_________________)
{
String str = (String) anObject;
Return str.length();
}
}
What parameter declaration can be used to complete the callback measure method?

A) Object anObject
B) String anObject
C) Object aString
D) String aString

Question 39

Which of the following statements about helper classes is true?

A) Helper classes must be inner classes.
B) Helper classes must implement interfaces.
C) Helper classes help reduce coupling.
D) Helper classes cannot contain instance variables.

Question 40

Consider the following class: public class Player implements Comparable
{
Private String name;
Private int goalsScored;
// other methods go here
Public int compareTo(Object otherObject)
{
__________________________________
Return (goalsScored - otherPlayer.goalsScored);
}
}
What statement can be used to complete the compareTo() method?

A) Player otherPlayer = otherObject;
B) Object otherPlayer = otherObject;
C) Player otherPlayer = (Player) otherObject;
D) Object otherPlayer = (Player) otherObject;

Question 41

What role does an interface play when using a mock class?

A) The mock class should be an interface that will be implemented by the real class.
B) The real class should be an interface that will be implemented by the mock class.
C) Interfaces are not involved when using mock classes.
D) An interface should be implemented by both the real class and the mock class to guarantee that the mock class accurately simulates the real class when used in a program.

Question 42

Which container is used to group multiple user-interface components together?

A) text area
B) table
C) panel
D) rectangle

Question 43

Which of the following code statements creates a graphical button which has "Calculate" as its label ?

A) Button JButton = new Button("Calculate").
B) button = new Button(JButton, "Calculate").
C) button = new JButton("Calculate").
D) JButton button = new JButton("Calculate").

Question 44

To respond to a button event, a listener must supply instructions for the ____ method of the ActionListener interface.

A) actionEvent.
B) actionPerformed
C) eventAction
D) eventResponse

Question 45

Consider the following class: public class ClickListener implements ActionListener
{
__________________________________________
{
System.out.println("mouse event ...");
}
}
Which of the following method headers should be used to complete the ClickListener class?

A) public void actionPerformed(ActionEvent event)
B) public void actionPerformed(ClickListener event)
C) public void actionPerformed()
D) public void actionPerformed(ActionListener event)

Question 46

To associate an event listener with a JButton component, you must use the ___ method of the JButton class.

A) addEventListener.
B) addActionListener.
C) addButtonListener.
D) addListener

Question 47

Event listeners are often installed as ____ classes so that they can have access to the surrounding fields, methods, and final variables.

A) Inner
B) Interface
C) Abstract
D) Helper

Question 48

____ are generated when the user presses a key, clicks a button, or selects a menu item.

A) Listeners
B) Interfaces.
C) Events.
D) Errors.

Question 49

Which of the following statements about listener classes is true?

A) A listener class cannot be declared as an anonymous inner class.
B) A listener class cannot be declared as an inner class.
C) A listener class must be declared as an inner class.
D) A listener class must be declared as an anonymous inner class.

Question 50

The methods of a/an ____ describe the actions to be taken when an event occurs.

A) event source
B) event listener
C) event interface
D) action source

Question 51

An inner class can access local variables from the enclosing scope only if they are declared as ____.

A) private
B) public
C) static
D) final

Question 52

A/an ____ belongs to a class whose methods describe the actions to be taken when a user clicks a user-interface graphical object.

A) Event listener
B) Event source
C) Action listener
D) Action method

Question 53

Which of the following statements will compile without error?

A) public interface AccountListener()
{
Void actionPerformed(AccountEvent event);
}
B) public interface AccountListener()
{
Void actionPerformed(AccountEvent);
}
C) public interface AccountListener
{
Void actionPerformed(AccountEvent event);
}
D) public abstract AccountListener
{
Void actionPerformed(AccountEvent event);
}

Question 54

Which of the following statements about an inner class is true?

A) An inner class may not be declared within a method of the enclosing scope.
B) An inner class may only be declared within a method of the enclosing scope.
C) An inner class can access variables from the enclosing scope only if they are passed as constructor or method parameters.
D) The methods of an inner class can access variables declared in the enclosing scope.

Question 55

Consider the following code snippet: public class ClickListener implements ActionListener
{
Public void actionPerformed(ActionEvent event)
{
System.out.println("I was clicked.");
}
}
Public class ButtonTester
{
Public static void main(String[] args)
{
JFrame frame = new JFrame();
JButton button = new JButton("Click me!");
Frame.add(button);
ActionListener listener = new ClickListener();
Button.addActionListener(listener);
)..
}
}
Which of the following statements is correct?

A) Class ButtonTester is an interface type.
B) A ClickListener object can be added as a listener for the action events that buttons generate.
C) Class ClickListener is an interface type.
D) Class ButtonTester implements an interface type.

Question 56

When an event occurs, the event source notifies all ____.

A) components
B) panels
C) interfaces
D) event listeners

Question 57

Consider the following code snippet:
Import ____________________
Import java.awt.event.ActionListener;
/**
An action listener that prints.
*/
Public class ClickListener implements ActionListener
{
Public void actionPerformed(ActionEvent event)
{
System.out.println("I was clicked.");
}
}
Which of the following statements will complete this code?

A) java.swing.event.ActionEvent;.
B) javax.swing.event.ActionEvent;
C) javax.awt.event.ActionEvent;
D) java.awt.event.ActionEvent;

Question 58

Which of the following is an event source?

A) A JButton object.
B) An event listener.
C) An inner class.
D) An event adapter.

Question 59

Which of the following statements about events and graphical user interface programs is true?
D) Your program must override the default methods to handle events.

A) Your program must instruct the Java window manager to send it notifications about specific types of events to which the program wishes to respond.
B) The Java window manager will automatically send your program notifications about all events that have occurred.
C) Your program must respond to notifications of all types of events that are sent to it by the Java window manager.

Question 60

Consider the following code snippet: JFrame frame = new JFrame();
JPanel panel = new JPanel
Which statement would add the panel to the frame?

A) frame.add(panel);
B) frame.add(JPanel panel);
C) frame.addComponent(panel);
D) frame.addComponent(JPanel panel);

Question 61

When you use a timer, you need to define a class that implements the ____ interface.

A) TimerListener
B) TimerActionListener
C) ActionListener
D) StartTimerListener

Question 62

Consider the following code snippet which is supposed to show the total order amount when the button is clicked: public static void main(String[] args)
{
Final Order myOrder = new Order();
JButton button = new JButton("Calculate");
Final JLabel label = new JLabel("Total amount due");
) . .
Class MyListener implements ActionListener
{
Public void actionPerformed(ActionEvent event)
{
Label.setText("Total amount due " + myOrder.getAmountDue());
}
}
ActionListener listener = new MyListener();
}
What is wrong with this code?

A) button should be declared as final
B) The listener has not been attached to the button.
C) The listener cannot access the methods of the myOrder object.
D) This code will display the total order amount.

Question 63

To build a user interface that contains graphical components, the components ____.

A) Must be added directly to a frame component.
B) Must each be added to a separate panel.
C) Must be added to a panel that is contained within a frame.
D) Must be added to a frame that is contained within a panel.

Question 64

Consider the following code snippet: class MyListener implements ActionListener
{
Public void actionPerformed(ActionEvent event)
{
System.out.println(event);
}
}
Timer t = new Timer(interval, listener);
T)start();
What is wrong with this code?

A) The Timer object should be declared before the MyListener class.
B) The listener has not been attached to the Timer object.
C) The Timer object must be declared as final.
D) There is nothing wrong with the code.

Question 65

The ____ class in the javax.swing package generates a sequence of events, spaced apart at even time intervals.

A) TimeClock
B) Timer
C) Clock
D) StopWatch

Question 66

The Timer class is found in the ____ package.

A) java.awt.
B) javax.awt.
C) java.swing.
D) javax.swing.

Question 67

Consider the following code snippet: final RectangleComponent component = new RectangleComponent();
MouseListener listener = new MousePressListener();
Component.addMouseListener(listener);
______________
Frame.add(component);
Frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
Frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Frame.setVisible(true);
Which of the following statements completes this code?

A) private static final int FRAME_WIDTH = 300;
B) private static final int FRAME_HEIGHT = 400;
C) Frame frame = new Frame();
D) JFrame frame = new JFrame();

Question 68

The ____ method should be called whenever you modify the shapes that the paintComponent method draws.

A) draw
B) paint
C) paintComponent
D) repaint

Question 69

Consider the following code snippet: public static void main(String[] args)
{
Final Order myOrder = new Order();
JButton button = new JButton("Calculate");
Final JLabel label = new JLabel("Total amount due");
) . .
Class MyListener implements ActionListener
{
Public void actionPerformed(ActionEvent event)
{
) . .
}
}
}
Which of the local variables can be accessed within the actionPerformed method?

A) Only button can be accessed..
B) All of the local variables can be accessed.
C) label and myOrder can be accessed.
D) Only myOrder can be accessed.

Question 70

Assume that the TimerListener class implements the ActionListener interface. If the actionPerformed method in TimerListener needs to be executed every second, what statement should be used to complete the following code segment? ActionListener listener = new TimerListener();
_________________________________ // missing statement
Timer.start();

A) Timer timer = new Timer(listener);
B) Timer timer = new Timer(1, listener);
C) Timer timer = new Timer(100, listener);
D) Timer timer = new Timer(1000, listener);

Question 71

Use the ____ method to specify the height and width of a graphical component when you add it to a panel.

A) setPreferredDimensions.
B) setInitialDimensions.
C) setPreferredSize.
D) setInitialSize.

Question 72

Suppose listener is an instance of a class that implements the MouseListener interface. How many methods does listener have?

A) 0
B) 1
C) 3
D) at least 5

Question 73

Consider the following code snippet: public static void main(String[] args)
{
Order myOrder = new Order();
JButton button = new JButton("Calculate");
JLabel label = new JLabel("Total amount due");
) . .
Class MyListener implements ActionListener
{
Public void actionPerformed(ActionEvent event)
{
Label.setText("Total amount due " + myOrder.getAmountDue());
}
}
}
What is wrong with this code?

A) label must be declared as final.
B) myOrder must be declared as final
C) label and myOrder must be declared as final
D) label and button must be declared as final.

Question 74

Consider the code snippet below: public class RectangleComponent extends JComponent
{
Private Rectangle box;
Private static final int BOX_X = 100;
Private static final int BOX_Y = 100;
Private static final int BOX_WIDTH = 20;
Private static final int BOX_HEIGHT = 30;
Public RectangleComponent()
{
// The rectangle that the paint method draws
Box = new Rectangle(BOX_X, BOX_Y,
BOX_WIDTH, BOX_HEIGHT);
}
Public void paintComponent(Graphics

A) repaint();
B) g2.draw(box);
C) box.setLocation(x, y);
D) private Rectangle box;
G) {
Super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
G2)draw(box);
}
Public void moveTo(int x, int y)
{
Box)setLocation(x, y);
Repaint();
}
}
Which statement causes the rectangle to appear at an updated location?

Question 75

A(n) ____ has an instance method addActionListener() for specifying which object is responsible for implementing the action associated with the object.

A) JFrame
B) JSlider
C) JButton
D) JLabel

Question 76

How do you specify what the program should do when the user clicks a button?

A) Specify the actions to take in a class that implements the ButtonListener interface.
B) Specify the actions to take in a class that implements the ButtonEvent interface .
C) Specify the actions to take in a class that implements the ActionListener interface.
D) Specify the actions to take in a class that implements the EventListener interface.

Question 77

Use the ____ method to add a mouse listener to a component.

A) addListener
B) addMouseListener
C) addActionListener
D) addMouseActionListener

Question 78

If the user presses and releases a mouse button in quick succession, which methods of the MouseListener interface are called?

A) mousePressed, mouseReleased, and mouseClicked.
B) mousePressed, mouseReleased, and mouseDblClicked
C) Only the mouseClicked method.
D) Only the mouseDblClicked method.

Question 79

You have a class which extends the JComponent class. In this class you have created a painted graphical object. Your code will change the data in the graphical object. What additional code is needed to ensure that the graphical object will be updated with the changed data?

A) You must call the component object's paintComponent() method.
B) You must call the component object's repaint() method.
C) You do not have to do anything - the component object will be automatically repainted when its data changes.
D) You must use a Timer object to cause the component object to be updated.

Question 80

Assuming that the ClickListener class implements the ActionListener interface, what statement should be used to complete the following code segment? ClickListener listener = new ClickListener();
JButton myButton = new JButton("Submit");
JPanel myPanel = new JPanel();
MyPanel.add(myButton);
______________________ // missing statement

A) myPanel.addActionListener(listener);
B) myButton.addActionListener(listener);
C) myPanel.addActionListener(myButton);
D) myButton.addActionListener(ClickListener);