Interfaces And Abstract Classes — Part 1 MCQs with Explanations

In Java, abstract classes can extend both abstract and concrete classes. When an abstract class extends another class (whether abstract or concrete), it inherits the properties and methods of that class. An abstract class is allowed to inherit from a concrete class and can override or use the methods from the superclass. Option A is incorrect because abstract classes can extend other classes. Option C is incorrect since there is no requirement for the superclass to be marked as "static." Option D is incorrect as the subclass does not need to be marked "final" to extend a class.

(3) is correct because an abstract class doesn't have to implement any or all of its interface's methods. (4) is correct because this method is correctly implemented ((7 > 4) is a boolean). (1) is incorrect because interfaces doesn't implement anything. (2) is incorrect because classes don't extend interfaces. (5) is incorrect because interface methods are implicitly public, so the methods being implemented must be public.

(3), (6). Both are legal class declarations. (1) is wrong because a class cannot be abstract and final "there would be no way to use such a class". (2) is wrong because interfaces and classes cannot be marked as static . (4) and (5) are wrong because classes and interfaces cannot be marked as protected .

Abstract class is not concrete class which means object cannot be created for abstract class, its requires extending it and then create the object of extended class.

The A a1 reference variable refers not to an instance of interface A, but to an instance of an anonymous (unnamed) class. So there is no compilation error.

Illegal modifier for the interface method InfA.getName(); only public and abstracts are permitted.

All the variables declared in interface is implicitly static and final , therefore can't change the value.

The options B, C and D are incorrect options as in Java we can declare an abstract class comprising of abstract and non-abstract methods that will not lead to any compilation error. Therefore, option A is the correct answer implying that the 't' instance of Test class invokes the display method, which is implemented in the Test class. The display method invokes myName() method declared int the TestAbstract class and prints the name.

The program will compile and execute successfully as you can declare methods with same name in an interface and the method of either interface can be used, implying the option a is incorrect. The option B and D are incorrect as the methods of an interface are implicitly public and abstract.

A contract specifying a set of methods that a class must implement is the correct answer to “What is an interface in Java”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Yes, a class can implement multiple interfaces is the correct answer to “In Java, can a class implement multiple interfaces”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

interface is the correct answer to “Which keyword is used to declare an interface in Java”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

To provide a base class with common methods and fields is the correct answer to “What is the purpose of an abstract class in Java”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

No, an abstract class cannot be instantiated is the correct answer to “In Java, can an abstract class be instantiated”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

To indicate that a class is implementing an interface is the correct answer to “What is the purpose of the "implements" keyword in Java”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Abstract class is the correct answer to “Which of the following can contain both abstract and non-abstract methods”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Yes, an interface can have constant (final) fields is the correct answer to “In Java, can an interface have fields (member variables)”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

To declare a method without providing an implementation is the correct answer to “What is the purpose of an abstract method in an abstract class or interface”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

abstract is the correct answer to “Which keyword is used to define an abstract method in Java”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Yes, starting from Java 9, interfaces can have private methods is the correct answer to “In Java, can an interface have private methods with implementations”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Implementation is the correct answer to “What is the result of the following code snippet? interface MyInterface { void myMethod(); } public class MyClass implements MyInterface { public void myMethod() { System.out.println("Implementation"); } public static void main(String[] args) { MyInterface obj = new MyClass(); obj.myMethod(); } }”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

To create a subclass is the correct answer to “What is the purpose of the "extends" keyword in Java”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Yes, an interface can extend multiple interfaces is the correct answer to “In Java, can an interface extend another interface”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Implementation is the correct answer to “What is the result of the following code snippet? abstract class MyAbstract { abstract void myMethod(); } class MyClass extends MyAbstract { void myMethod() { System.out.println("Implementation"); } public static void main(String[] args) { MyAbstract obj = new MyClass(); obj.myMethod(); } }”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Yes, an abstract class can have both abstract and non-abstract methods is the correct answer to “In Java, can an abstract class have non-abstract methods”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

To specify the default implementation of a method is the correct answer to “What is the purpose of the "default" keyword in Java interfaces”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Default Implementation is the correct answer to “What is the result of the following code snippet? interface MyInterface { default void myMethod() { System.out.println("Default Implementation"); } } class MyClass implements MyInterface { public static void main(String[] args) { MyInterface obj = new MyClass(); obj.myMethod(); } }”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Yes, a class can implement an interface and extend an abstract class is the correct answer to “In Java, can a class implement an interface and extend an abstract class simultaneously”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

To indicate that a class, method, or variable cannot be further extended, overridden, or modified is the correct answer to “What is the purpose of the "final" keyword in Java”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Yes, an abstract class can have constructors is the correct answer to “In Java, can an abstract class have constructors”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Constructor is the correct answer to “What is the result of the following code snippet? abstract class MyAbstract { MyAbstract() { System.out.println("Constructor"); } } class MyClass extends MyAbstract { public static void main(String[] args) { MyClass obj = new MyClass(); } }”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Yes, starting from Java 8, interfaces can have static methods with implementations is the correct answer to “In Java, can an interface have static methods with implementations”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Static Method is the correct answer to “What is the result of the following code snippet? interface MyInterface { static void myMethod() { System.out.println("Static Method"); } } class MyClass implements MyInterface { public static void main(String[] args) { MyInterface.myMethod(); } }”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Yes, starting from Java 9, abstract classes can have private methods with implementations is the correct answer to “In Java, can an abstract class have private methods with implementations”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Compilation error is the correct answer to “What is the result of the following code snippet? abstract class MyAbstract { private void myMethod() { System.out.println("Private Method"); } } class MyClass extends MyAbstract { public static void main(String[] args) { MyClass obj = new MyClass(); obj.myMethod(); } }”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Yes, an abstract class can have static methods with implementations is the correct answer to “In Java, can an abstract class have static methods with implementations”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Static Method is the correct answer to “What is the result of the following code snippet? abstract class MyAbstract { static void myMethod() { System.out.println("Static Method"); } } class MyClass extends MyAbstract { public static void main(String[] args) { MyAbstract.myMethod(); } }”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Yes, starting from Java 8, abstract classes can have default methods with implementations is the correct answer to “In Java, can an abstract class have default methods with implementations”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

Class School must be defined abstract. is the correct answer to “Given the following piece of code: public class School{ public abstract double numberOfStudent(); } which of the following statements is true”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.

abstract class A { abstract void unfinished(); } is the correct answer to “Which of the following class definitions defines a legal abstract class”. This question is standard in competitive examination syllabi for Interfaces And Abstract Classes.