Java Study Group Chapter 1

1. A class can ...

Extend only a single class and implement only a single interface

Extend only a single class but implement multiple interfaces

Extend multiple classes but implement only a single interface

Extend multiple classes and implement multiple interfaces

A class can extend only a single class because Java does not support multiple inheritance for classes. However, it can implement multiple interfaces because Java allows a class to implement multiple interfaces to achieve multiple inheritance-like behavior.

Explanation

A class can extend only a single class because Java does not support multiple inheritance for classes. However, it can implement multiple interfaces because Java allows a class to implement multiple interfaces to achieve multiple inheritance-like behavior.

2. Given the following classes defined in separate files:

What will the output be on running the Test class?

Compiler error for statement v=c

Prints: -Vehicle:Driving--Car:Driving--Vehicle:Driving-

Runtime exception for statement v=c

Prints:-Vehicle:Driving--Car:Driving--Car:Driving-

Prints:-Vehicle:Driving--Car:Driving-

The output will be "Prints: -Vehicle:Driving--Car:Driving--Car:Driving-". This is because the statement "v=c" assigns the object of the Car class to the reference variable v of the Vehicle class. Since the Car class is a subclass of the Vehicle class, it inherits the drive() method from the Vehicle class. Therefore, when the drive() method is called on the object v, it executes the drive() method of the Car class. The output is printed three times because the drive() method is called three times in the Test class.

Explanation

The output will be "Prints: -Vehicle:Driving--Car:Driving--Car:Driving-". This is because the statement "v=c" assigns the object of the Car class to the reference variable v of the Vehicle class. Since the Car class is a subclass of the Vehicle class, it inherits the drive() method from the Vehicle class. Therefore, when the drive() method is called on the object v, it executes the drive() method of the Car class. The output is printed three times because the drive() method is called three times in the Test class.

3. What is the correct order?

Import, package, class

Class, import, package

Package, import, class

Package, class, import

Import, class, package

The correct order is package, import, class. In Java, the package statement is used to define the package that the class belongs to. The import statement is used to import other classes or packages that are needed in the current class. Finally, the class statement is used to define the class itself. Therefore, the correct order is to first define the package, then import any necessary classes or packages, and finally define the class.

Explanation

The correct order is package, import, class. In Java, the package statement is used to define the package that the class belongs to. The import statement is used to import other classes or packages that are needed in the current class. Finally, the class statement is used to define the class itself. Therefore, the correct order is to first define the package, then import any necessary classes or packages, and finally define the class.

4. Which of the following are Java keywords?

Goto

Malloc

Implementable

Extends

New

Delete

not-available-via-ai

Explanation

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5. Which are true?

Abstract interfaces can have final methods.

The first concrete subclass must implement all abstract methods of its superclass.

Abstract classes cannot have static methods.

Interfaces can declare instance variables.

The first statement is true. When a class extends an abstract class, it must provide implementations for all the abstract methods defined in the superclass.

The second statement is also true. Abstract classes cannot have static methods because static methods are associated with the class itself, not with any particular instance of the class.

Therefore, the correct answer is that the first concrete subclass must implement all abstract methods of its superclass and abstract classes cannot have static methods.

Explanation

The first statement is true. When a class extends an abstract class, it must provide implementations for all the abstract methods defined in the superclass.

The second statement is also true. Abstract classes cannot have static methods because static methods are associated with the class itself, not with any particular instance of the class.

Therefore, the correct answer is that the first concrete subclass must implement all abstract methods of its superclass and abstract classes cannot have static methods.

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