Question 1

____ methods must be implemented when using an interface.

Accepted Answer

Abstract methods must be implemented when using an interface.

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?

Accepted Answer

The default access level for methods in an interface is public, while the default access level for methods in a class is package access. Therefore, the getMeasure method in the Inventory class must be declared as public in order to satisfy the Measurable interface.

Question 3

Which of the following statements about interfaces is NOT true?

Accepted Answer

A class can implement multiple interface types, not just one.

Question 4

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

Accepted Answer

A Java interface can contain zero or more methods, so it is not required to have more than one method.

Question 5

Which of the following statements about an interface is true?

Accepted Answer

An interface in programming defines a contract with methods that must be implemented by a class, but it does not contain instance variables.

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?

Accepted Answer

Coin implements Measurable, so a Coin object can be assigned to a Measurable variable.

Question 7

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

Accepted Answer

The getMeasure() method must be declared as public because it is implementing a method from the Measurable interface, which requires public access.

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 ?

Accepted Answer

In Java, methods in a class are not public by default; they need to be explicitly declared as public to be accessible from outside the class.

Question 9

Which of the following statements about abstract methods is true?

Accepted Answer

An abstract method is a method that is declared without any implementation. It has only a method signature, which includes the method name, parameters, and return type, but no code in the body of the method. Option A correctly describes the characteristics of an abstract method.

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?

Accepted Answer

The method header must match the signature defined in the Encryptable interface, which is `void encrypt(String key)`.

Question 11

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

Accepted Answer

In Java, a class uses the keyword "implements" followed by the name of the interface to indicate that it is implementing the interface.

Question 12

____ can reduce the coupling between classes.

Accepted Answer

Interfaces can reduce the coupling between classes by allowing classes to communicate through a common set of methods without needing to know the specific details of each other's implementations.

Question 13

Which statement about methods in an interface is true?

Accepted Answer

In Java, all methods in an interface are implicitly public and abstract, meaning they do not need to be explicitly declared as 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?

Accepted Answer

In an interface, methods are implicitly public and abstract, so the correct declaration is simply "void resize();".

Question 15

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

Accepted Answer

Casting object types can lead to a ClassCastException if the object is not an instance of the target class, posing a risk of an exception.

Question 16

Which of the following statements about interfaces is true?

Accepted Answer

An interface variable can refer to an object only if the object's class implements the interface, allowing the object to be treated as an instance of the interface type.

Question 17

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

Accepted Answer

An abstract method is a method that is declared without an implementation and must be implemented by subclasses.

Question 18

Which of the following statements about interfaces is NOT true?

Accepted Answer

Interfaces cannot have private methods; they can only have public methods (and default or static methods in some languages like Java).

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?

Accepted Answer

In an interface, all variables are implicitly public, static, and final, so they do not need to be explicitly declared as such.

Question 20

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

Accepted Answer

A class type can be converted to an interface type if the class implements that interface.

Quiz 10: Interfaces

____ methods must be implemented when using an interface.

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?

Which of the following statements about interfaces is NOT true?

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

Which of the following statements about an interface is true?

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

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

Which of the following statements about abstract methods is true?

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

____ can reduce the coupling between classes.

Which statement about methods in an interface is true?

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?

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

Which of the following statements about interfaces is true?

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

Which of the following statements about interfaces is NOT true?

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?

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