Deck 10: Interfaces

Question 1

Consider the following declarations: Which of the following method headers should be used to complete the SecretText class?
A.public void encrypt()
B.void encrypt(String aKey)
C.public void encrypt(String aKey)
D.public String encrypt(String aKey)

Answer 1

public void encrypt(String aKey)

Question 2

Which statement about methods in an interface is true?
A.All methods in an interface must be explicitly declared as private or public.
B.All methods in an interface are automatically public.
C.All methods in an interface are automatically private.
D.All methods in an interface are automatically static.

Answer 2

All methods in an interface are automatically public.

Question 3

Which of the following statements about interfaces is NOT true?
A.Interfaces can reduce the coupling between classes.
B.A class can implement only one interface type.
C.An interface cannot have instance variables.
D.Interfaces can make code more reusable.

Answer 3

A class can implement only one interface type.

Question 4

Consider the following code snippet: Which of the following statements is true?
A.LARGE_CHANGE and SMALL_CHANGE are instance variables.
B.LARGE_CHANGE and SMALL_CHANGE are automatically public static final.
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 5

Which of the following statements about interfaces is NOT true?
A.An interface can supply a default implementation.
B.Interfaces can make code more reusable.
C.An interface can describe the state that should be maintained.
D.An interface describes the behavior that an implementation should supply.

Question 6

Suppose you are writing an interface called Resizable, which includes one void method called resize that accepts no parameters.

Question 7

Consider the definition of the Measurable interface and the code snippet defining the Inventory class: Why is it necessary to declare getMeasure as public in the Inventory class?
A.It is necessary only to allow other classes to use this method.
B.It is not necessary to declare this method as public.
C.All methods in an interface are private by default.
D.All methods in a class are not public by default.

Question 8

Using the following definitions of the Measurable and Named interfaces. Assume BankAccount provides the code for the getMeasure() and getName() methods.Which of the following could correctly represent the class header for BankAccount?
A.public class BankAccount extends Measurable implements Named
B.public class BankAccount implements Measurable, Named
C.public interface BankAccount implements Measurable, Named
D.public class BankAccount extends Measurable, Named

Question 9

What type of edge does UML use to denote interface implementation?
A.A dotted arrow from the interface to the class terminated with a triangular tip.
B.A dotted arrow from the class to the interface terminated with an open arrow tip.
C.A dotted arrow from the interface to the class terminated with an open arrow tip.
D.A dotted arrow from the class to the interface terminated with a triangular tip.

Question 10

A class that implements an interface must provide an implementation for all ____ methods.
A.private
B.final
C.static
D.abstract

Question 11

Consider the following code snippet: Which of the following completes the interface declaration correctly?
A.final
B.private
C.static
D.public

Question 12

To use an interface, a class header should include which of the following?
A.The keyword extends and the name of the interface
B.The keyword extends and the name of an abstract method in 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 13

Consider the definition of the Measurable interface and the code snippet defining the Inventory class: The compiler complains that the getMeasure method has a weaker access level than the Measurable interface.Why?
A.The getMeasure method was declared as private in the Measurable interface.
B.The variable onHandCount was not declared with public access.
C.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.
D.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.

Question 14

In UML, a dotted arrow with a triangular tip denotes ____________________.
A.interface implementation
B.dependency
C.inheritance
D.aggregation

Question 15

Which of the following statements about an interface is true?
A.An interface has both public and private methods.
B.An interface has methods and instance variables.
C.An interface has methods but no instance variables.
D.An interface has neither methods nor instance variables.

Question 16

Which of the following statements is correct about inheritance and interfaces?
A.A class can extend multiple classes and can implement multiple interfaces.
B.A class can extend at most one class and can implement at most one interface.
C.A class can extend multiple classes and can implement at most one interface.
D.A class can extend at most one class and can implement multiple interfaces.

Question 17

Consider the definition of the Measurable interface and the code snippet defining the Inventory class: What is wrong with this code?
A.The getMeasure() method must be declared as private.
B.The getMeasure() method must be declared as public.
C.The getMeasure() method must include the implements keyword.
D.The getMeasure() method must not have any code within it.

Question 18

A method that has no implementation is called a/an ____ method.
A.abstract
B.overloaded
C.interface
D.implementation

Question 19

Which of the following statements about abstract methods is true?
A.An abstract method has only a name and a return type, but no parameters or code in its body.
B.An abstract method has a name, a return type, and code in its body, but has no parameters.
C.An abstract method has parameters, a return type, and code in its body, but has no defined name.
D.An abstract method has a name, parameters, and a return type, but no code in the body of the method.

Question 20

Which of the following statements about a Java interface is NOT true?
A.A Java interface must contain more than one method.
B.A Java interface defines a set of methods that are required.
C.A Java interface specifies behavior that a class will implement.
D.All methods in a Java interface must be public.

Question 21

Assume a class extends another class and implements an interface, both of which define the same method.Which statement is true about this conflict of inherited methods?
A.The compiler will generate an error due to the conflict.
B.The code compiles but generates an exception at run time due to the conflict.
C.The subclass inherits the superclass method and ignores the default method from the interface.
D.There is no conflict because interfaces cannot provide method implementation.

Question 22

Using the given definition of the Measurable interface: Which of the following statements is true?
A.The code does not compile because a variable of type Measurable does not have a getBalance method.
B.The code compiles but generates an exception at run time because a Measurable object reference does not have a getBalance method.
C.The code executes, displaying the balance of the bank account.
D.The code does not compile because you cannot assign a BankAccount object to a variable of type Measurable.

Question 23

Consider the following class: Which is the best statement to use to complete the compareTo() method?
A.return Integer.compare(otherTemp.value, value)
B.return (value - otherTemp.value)
C.return (otherTemp.value - value)
D.return Integer.compare(value, otherTemp.value)

Question 24

Which of the following can potentially be changed when implementing an interface?
A.The return type of a method in the interface.
B.The types of parameters of a method in the interface.
C.The name of a method in the interface.
D.You cannot change the name, return type, or types of parameters of a method in the interface.

Question 25

Assume a class implements two interfaces, both of which define a default method with the same signature.Which statement is true about this conflict of inherited methods?
A.The code compiles but generates an exception at run time due to the conflict.
B.The code compiles and the implementation is chosen at run time.
C.The class must override the method and provide its own implementation.
D.There is no conflict because interfaces cannot provide method implementation.

Question 26

Which of the following is true about interface types and abstract classes?
A.An interface type cannot be instantiated whereas an abstract class can.
B.An interface type cannot have instance variables whereas an abstract class can.
C.An abstract class can provide method implementation whereas an interface type cannot.
D.An interface type cannot have constants whereas an abstract class can.

Question 27

Assume that the Measurable interface is defined with a static sum method that computes the sum of the Measurable objects passed in as an array, and that BankAccount implements the Measurable interface.Also assume that there is a variable branchAccounts that is an object reference to a populated array of BankAccount objects for a bank branch.Which of the following represents a correct invocation of the sum method to find the total balance of all accounts at the branch?
A.Arrays.sum(branchAccounts)
B.BankAccount.sum(branchAccounts)
C.Measurable.sum(branchAccounts)
D.branchAccounts.sum()

Question 28

The method below is designed to return the smaller of two Comparable objects received as arguments.Assume that the objects are instances of the same class.Select the correct expression to complete the method.
A.value1.compareTo(value2) > 0
B.value1 < value2
C.value1.compareTo(value2) < 0
D.value1.compareTo(value2) == 0

Question 29

Using the given definition of the Measurable interface: Which of the following statements is true?
A.The code executes, displaying the measure of the Measurable object.
B.The code does not compile because interface types cannot be instantiated.
C.The code compiles but generates an exception at run time because getMeasure does not return a String.
D.The code compiles but generates an exception at run time because m does not reference a BankAccount object.

Question 30

Which of the following is true about a default method in an interface declaration?
A.A default method is a static method that does not have an implicit parameter.
B.A default method does not provide an implementation.
C.A class that implements the interface cannot override the default behavior.
D.A class that implements the interface can inherit the default behavior.

Question 31

Consider the following class: What statement can be used to complete the compareTo() method?
A.otherGame.score - score
B.return (otherGame.score - score)
C.score - otherGame.score
D.return (score - otherGame.score)

Question 32

Consider the following code snippet: Which of the following completes the interface declaration correctly?
A.public
B.private
C.final
D.default

Question 33

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

Question 34

Using the given definition of the Measurable interface: Select the correct expression to display the balance of the bank account.
A.m.BankAccount.getBalance()
B.m.getBalance()
C.((BankAccount) m).getBalance()
D.m.super.getBalance()

Question 35

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

Question 36

Consider the following class: What statement can be used to complete the compareTo() method?
A.Player otherPlayer = (Player) otherObject;
B.Object otherPlayer = (Player) otherObject;
C.Object otherPlayer = otherObject;
D.Player otherPlayer = otherObject;

Question 37

Which of the following are not allowed in a Java 8 interface declaration?
A.instance variables
B.default methods
C.static methods
D.constants

Question 38

Consider the following code snippet.

Question 39

If you have multiple classes in your program that have implemented the same interface in

Question 40

Consider the following declarations:
A.increaseSize()
B.decreaseSize()
C.display(5)
D.display()

Question 41

You wish to implement a callback method for an object created from a library class that you cannot change.What is the preferred way to accomplish this?
A.Extend the library class.
B.Use an inner class in the interface.
C.Create a new class that mimics the library class.
D.Use a helper class that implements the callback method.

Question 42

Consider the following class: Which is the best statement to use to complete the compareTo() method?
A.return (otherStock.price - price)
B.return Integer.compare(price, otherStock.price)
C.return Double.compare(otherStock.price, price)
D.return Double.compare(price, otherStock.price)

Question 43

Which of the following statements about lambda expressions is NOT true?
A.Lambda expressions are used to define a single function of a functional interface.
B.A lambda expression defines the parameters and return value of a method in a compact notation.
C.Lambda expressions are a convenient notation for callbacks.
D.Lambda expressions cannot contain a method body enclosed in braces with a return statement.

Question 44

What role does an interface play when using a mock class?
A.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.
B.The mock class should be an interface that will be implemented by the real class.
C.Interfaces are not involved when using mock classes.
D.The real class should be an interface that will be implemented by the mock class.

Question 45

An ____ belongs to a class whose methods describe the actions to be taken when a user clicks a user-interface graphical object.
A.event source
B.event listener
C.action method
D.action listener

Question 46

Which of the following statements about an inner class is true?
A.An inner class is used for a utility class that should be visible elsewhere in the program.
B.An inner class that is defined inside a method is publicly accessible.
C.An inner class that is defined inside a method is not publicly accessible.
D.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.

Question 47

Consider the following class: 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 48

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 must be an interface.
C.A mock class provides a simplified implementation of the services of the actual class.
D.A mock class provides a complete implementation of the services of the actual class.

Question 49

Consider the following code snippet that uses the parameterized Comparable interface.

Question 50

Which of the following statements about events and graphical user interface programs is true?
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 override the default methods to handle events.
D.Your program must respond to notifications of all types of events that are sent to it by the Java window manager.

Question 51

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

Question 52

Consider the following code snippet: Which of the following statements correctly clones the account?
A.BankAccount clonedAccount = Object.clone(account);
B.BankAccount clonedAccount = account.super.clone();
C.BankAccount clonedAccount = account.clone();
D.BankAccount clonedAccount = (BankAccount) account.clone();

Question 53

Assuming that interface Resizable is declared elsewhere, consider the following class declaration: Which of the following declarations can be used to complete the main method?
A.SizeModifier something = new Resizable();
B.Resizable something = new Resizable();
C.Resizable something = new InnerClassExample();
D.Resizable something = new SizeModifier();

Question 54

Which of the following is an event source?
A.An inner class.
B.An event listener.
C.A JButton object.
D.An event adapter.

Question 55

Which of the following correctly defines a functional interface that, given an object, returns the value of a Coin?
A.(Object obj) => ((Coin) obj).getValue()
B.(Object obj) -> (Coin) obj.getValue()
C.(Object obj) => (Coin) obj.getValue()
D.(Object obj) -> ((Coin) obj).getValue()

Question 56

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.protected
B.interface
C.abstract
D.inner

Question 57

____ are generated when the user presses a key, clicks a button, or selects a menu item.
A.Errors
B.Interfaces
C.Events
D.Listeners

Question 58

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 abstract class.
C.an anonymous object.
D.an abstract object.

Question 59

Which of the following statements about the Object.clone method is NOT true?
A.Its return type is the same as the cloned object.
B.It returns a new object that has a state identical to the cloned object.
C.If the object being cloned does not implement the Cloneable interface, then it throws an exception.
D.It does not clone mutable instance variables.

Question 60

Consider the following declarations: What parameter declaration can be used to complete the callback measure method?
A.String aString
B.Object aString
C.Object anObject
D.String anObject

Question 61

Consider the following code snippet which is supposed to show the total order amount when the button is clicked: What is wrong with this code?
A.button should be declared as final
B.There is no error.
C.The listener cannot access the methods of the myOrder object.
D.The listener has not been attached to the button.

Question 62

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.The methods of an inner class can access variables declared in the enclosing scope.
C.An inner class may only be declared within a method of the enclosing scope.
D.An inner class can access variables from the enclosing scope only if they are passed as constructor or method parameters.

Question 63

Which of the following is an example of a functional interface, having a single abstract method?
A.ActionListener
B.KeyListener
C.MouseListener
D.MouseAdapter

Question 64

Event listeners are often installed as ____ classes so that they can have access to the surrounding fields, methods, and final variables.
A.interface
B.helper
C.inner
D.abstract

Question 65

Which of the following correctly completes the Java statement shown to add a listener to a button using a lambda expression?
button.addActionListener(_________________________________);
A.(ActionEvent event) => System.out.println("Clicked!")
B.lambda((ActionEvent event) -> System.out.println("Clicked!"))
C.(ActionEvent event) -> System.out.println("Clicked!")
D.lambda(ActionEvent event, System.out.println("Clicked!"))

Question 66

When an event occurs, the event source notifies all ____.
A.event listeners
B.components
C.panels
D.interfaces

Question 67

To build a user interface that contains graphical components, the components ____.
A.must each be added to a separate panel.
B.must be added directly to a frame component.
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 68

To associate an event listener with a JButton component, you must use the ___ method of the JButton class.
A.addActionListener
B.addButtonListener
C.addListener
D.addEventListener

Question 69

A ____ has an addActionListener() method for specifying which object is responsible for implementing the action associated with the object.
A.JSlider
B.JButton
C.JFrame
D.JLabel

Question 70

Listeners are typically implemented as inner classes.Which of the following statements is NOT true about inner class access to variables from the surrounding class?
A.Inner class objects created inside a static method can only access static variables.
B.Local variables that are accessed by an inner class method must not change after they have been initialized.
C.Methods of an inner class cannot access variables from the surrounding class.
D.An inner class can access instance variables of the surrounding class if the instance variable belongs to the object that constructed the inner class object.

Question 71

Consider the following code snippet: Which of the following statements is correct?
A.A ClickListener object has been added as a listener for the action events that buttons generate.
B.Class ClickListener is an interface type.
C.Class ButtonTester implements an interface type.
D.Class ButtonTester is an interface type.

Question 72

Consider the following code snippet: Which of the following statements will complete this code?
A.java.swing.event.ActionEvent;.
B.javax.awt.event.ActionEvent;
C.java.awt.event.ActionEvent;
D.javax.swing.event.ActionEvent;

Question 73

To respond to a button event, a listener must supply instructions for the ____ method of the ActionListener interface.
A.eventAction
B.actionPerformed
C.actionEvent
D.eventResponse

Question 74

Consider the following code snippet: Which statement would add the panel to the frame?
A.frame.add(JPanel panel);
B.frame.addComponent(JPanel panel);
C.frame.add(panel);
D.frame.addComponent(panel);

Question 75

Assuming that the ClickListener class implements the ActionListener interface, what statement should be used to complete the following code segment?
A.myButton.addActionListener(listener);
B.myPanel.addActionListener(myButton);
C.myPanel.addActionListener(listener);
D.myButton.addActionListener(ClickListener);

Question 76

The methods of an ____ describe the actions to be taken when an event occurs.
A.event source
B.event interface
C.action source
D.event listener

Question 77

Which of the following code statements creates a graphical button that has "Calculate" as its label ?
A.JButton button = new JButton().label("Calculate");
B.JButton button = new JButton().add("Calculate");
C.JButton button = new JButton("Calculate");
D.Button button = new Button("Calculate");

Question 78

Which container is used to group multiple user-interface components together?
A.text area
B.rectangle
C.table
D.panel

Question 79

Which of the following correctly defines a ButtonListener as an inner class and creates an instance of ButtonListener as a listener for the button?

Question 80

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