Master the Java Interview: Top 100 Java MCQ Questions and Answers

1. How is a class defined in Java? 

   a) Using the “def” keyword followed by the class name 

   b) Using the “class” keyword followed by the class name 

   c) Using the “class” keyword followed by the class name and then the superclass name 

   d) Using the “class” keyword followed by the superclass name 

   Answer: b) Using the “class” keyword followed by the class name 

   Explanation: In Java, classes are defined using the “class” keyword followed by the name of the class. 

2. What keyword is used to indicate inheritance in a class definition? 

   a) extends 

   b) implements 

   c) inherits 

   d) extendsFromClass 

   Answer: a) extends 

   Explanation: In Java, the “extends” keyword is used to indicate that a class is a subclass of another class. 

3. Where are instance variables typically defined in a class? 

   a) Inside method definitions 

   b) Just before the class declaration 

   c) Outside method definitions within the class declaration 

   d) Inside the constructor method 

   Answer: c) Outside method definitions within the class declaration 

   Explanation: Instance variables are defined within the class declaration, typically just after the class name. 

4. What keyword is used to declare constants in Java? 

   a) const 

   b) static 

   c) final 

   d) constant 

   Answer: c) final 

   Explanation: Constants in Java are declared using the “final” keyword. 

5. Which type of variables are global to a class and its instances? 

   a) Local variables 

   b) Constant variables 

   c) Class variables 

   d) Instance variables 

   Answer: c) Class variables 

   Explanation: Class variables are global to a class and its instances. 

6. What is the keyword used to define methods in Java? 

   a) function 

   b) method 

   c) define 

   d) void 

   Answer: d) void 

   Explanation: In Java, methods are defined using the “void” keyword if they do not return any value. 

7. Which keyword is used to refer to the current object within a method definition? 

   a) current 

   b) self 

   c) this 

   d) object 

   Answer: c) this 

   Explanation: The “this” keyword is used to refer to the current object within a method definition in Java. 

8. What is method overloading in Java? 

   a) Defining multiple methods with the same name but different return types 

   b) Defining multiple methods with the same name but different parameters 

   c) Defining multiple methods with the same name and same return type 

   d) Defining multiple methods with the same name and access level 

   Answer: b) Defining multiple methods with the same name but different parameters 

   Explanation: Method overloading in Java allows defining multiple methods with the same name but different parameters. 

9. How are variables passed to methods in Java? 

   a) By value 

   b) By reference 

   c) By copy 

   d) By pointer 

   Answer: b) By reference 

   Explanation: In Java, object parameters are passed by reference to methods, meaning modifications to the object inside the method affect the original object. 

10. What does Java use to prevent naming conflicts between local and instance variables? 

    a) It automatically renames local variables 

    b) It raises an error during compilation 

    c) It gives precedence to instance variables 

    d) It requires explicit casting 

    Answer: c) It gives precedence to instance variables 

    Explanation: In Java, instance variables take precedence over local variables if they have the same name, avoiding naming conflicts. 

1. How are class methods defined in Java?
a) By using the “instance” keyword followed by the method name
b) By using the “class” keyword followed by the method name
c) By using the “static” keyword followed by the method definition
d) By using the “global” keyword followed by the method name

2. What is the purpose of class methods in Java?
a) To operate on a particular object or affect that object directly
b) To define methods that are available to any other classes or objects
c) To create instances of classes with specific parameters
d) To handle command-line arguments passed to Java programs

Answer: b) To define methods that are available to any other classes or objects

Explanation: Class methods in Java are global to the class itself and are available to any other classes or objects.

3. How are command-line arguments passed to a Java program handled?
a) They are stored in an array of integers and accessed using the main() method
b) They are passed directly as parameters to the main() method
c) They are stored in an array of strings and accessed using the main() method
d) They are stored in a separate file and accessed using the System.in stream

Answer: c) They are stored in an array of strings and accessed using the main() method

Explanation: Command-line arguments passed to a Java program are stored in an array of strings, which is then passed to the main() method for handling.

1. What does method overloading in Java allow you to do? 

   – A) Create methods with the same name and different signatures 

   – B) Create methods with different names and the same signatures 

   – C) Create methods with different return types but the same names and signatures 

   – D) Create methods with the same name and signature 

   Answer: A) Create methods with the same name and different signatures 

   Explanation: Method overloading enables you to create methods with the same name but different signatures, either in terms of the number or types of arguments. 

2. What is the key factor that Java uses to differentiate overloaded methods with the same name? 

   – A) Return type 

   – B) Method name 

   – C) Number and type of parameters 

   – D) Method body 

   Answer: C) Number and type of parameters 

   Explanation: Java distinguishes overloaded methods based on the number and types of parameters rather than the return type or method name. 

3. Which keyword is used to call a constructor defined in the same class? 

   – A) super 

   – B) this 

   – C) constructor 

   – D) new 

   Answer: B) this 

   Explanation: The `this` keyword is used to call a constructor defined in the same class. 

4. What is a constructor method in Java? 

   – A) A method with the same name as the class and a return type 

   – B) A method used to initialize object instance variables 

   – C) A method used to define overloaded methods 

   – D) A method used to call other methods in a class 

   Answer: B) A method used to initialize object instance variables 

   Explanation: Constructor methods are special methods used to initialize object instance variables when an object is created. 

5. How do you override a method in a subclass to replace the original definition completely? 

   – A) By using the `override` keyword 

   – B) By defining a method with a different name 

   – C) By defining a method with the same name, return type, and parameter list 

   – D) By using the `super` keyword 

   Answer: C) By defining a method with the same name, return type, and parameter list 

   Explanation: To override a method completely, you define a method in the subclass with the same name, return type, and parameter list as the method in the superclass. 

6. When overriding a method in a subclass, how can you call the original method defined in the superclass? 

   – A) By using the `this` keyword 

   – B) By using the `super` keyword 

   – C) By using the `override` keyword 

   – D) By defining a method with a different name 

   Answer: B) By using the `super` keyword 

   Explanation: You can call the original method defined in the superclass from the subclass using the `super` keyword. 

7. In method overriding, what is the purpose of calling the original method from within the overridden method? 

   – A) To replace the original method completely 

   – B) To augment the original method with additional behavior 

   – C) To hide the original method definition 

   – D) To define a new method with the same name 

   Answer: B) To augment the original method with additional behavior 

   Explanation: Calling the original method from within the overridden method allows you to add additional behavior to the original method’s functionality. 

8. Which keyword is used to refer to the current class’s superclass? 

   – A) super 

   – B) this 

   – C) extends 

   – D) parent 

   Answer: A) super 

   Explanation: The `super` keyword is used to refer to the current class’s superclass in Java. 

9. What is the primary difference between method overloading and method overriding? 

   – A) Method overloading involves defining a new method with the same name, while method overriding involves replacing the original method definition. 

   – B) Method overloading involves defining multiple methods with the same name but different signatures, while method overriding involves defining a method in a subclass with the same signature as a method in the superclass. 

   – C) Method overloading involves calling the original method from within the overridden method, while method overriding does not. 

   – D) Method overloading can only be done within the same class, while method overriding can be done across different classes. 

   Answer: B) Method overloading involves defining multiple methods with the same name but different signatures, while method overriding involves defining a method in a subclass with the same signature as a method in the superclass. 

   Explanation: Method overloading is about creating multiple methods with the same name but different signatures, whereas method overriding is about redefining a method in a subclass with the same signature as a method in the superclass. 

10. When you define a method with the same name as a method in a superclass, what happens if the signatures of the methods are different? 

   – A) The method in the subclass hides the method in the superclass. 

   – B) The method in the superclass hides the method in the subclass. 

   – C) Both methods are accessible from instances of the subclass. 

   – D) The compiler throws an error. 

   Answer: A) The method in the subclass hides the method in the superclass. 

   Explanation: If you define a method with the same name as a method in a superclass but with different signatures, the method in the subclass hides the method in the superclass. This is method hiding, not overriding. 

1. Why can constructors not be technically overridden in Java? 

   – A) Because they always have the same name as the current class 

   – B) Because they have a fixed signature 

   – C) Because they cannot have parameters 

   – D) Because they are static methods 

   Answer: A) Because they always have the same name as the current class 

   Explanation: Constructors in Java always have the same name as the class they belong to, so when you define a constructor in a subclass, you’re creating a new constructor for that subclass instead of overriding the constructor of the superclass. 

2. How can you call a constructor of the immediate superclass from a subclass constructor? 

   – A) By using the `super()` method 

   – B) By using the `this()` method 

   – C) By using the `extends` keyword 

   – D) By using the `constructor()` keyword 

   Answer: A) By using the `super()` method 

   Explanation: In a subclass constructor, you can call a constructor of the immediate superclass using the `super()` method followed by any required arguments. 

3. In the example provided with the `NamedPoint` class, why is it recommended to call the superclass constructor using `super(x, y)`? 

   – A) To ensure proper initialization of superclass instance variables 

   – B) To avoid compiler errors 

   – C) To prevent inheritance conflicts 

   – D) To improve performance 

   Answer: A) To ensure proper initialization of superclass instance variables 

   Explanation: Calling the superclass constructor ensures that the superclass’s instance variables are properly initialized, even if you are not explicitly aware of how the superclass initializes itself. 

4. What is the purpose of finalizer methods in Java? 

   – A) To initialize objects 

   – B) To optimize the removal of objects before garbage collection 

   – C) To override superclass constructors 

   – D) To define constructors for subclasses 

   Answer: B) To optimize the removal of objects before garbage collection 

   Explanation: Finalizer methods are called just before an object is garbage-collected, and they are typically used to perform cleanup tasks or optimizations before the object is removed from memory. 

5. What is a limitation of finalizer methods in Java? 

   – A) They are guaranteed to be called immediately after an object becomes eligible for garbage collection. 

   – B) They can only be called by the garbage collector. 

   – C) They can trigger garbage collection. 

   – D) They have no restrictions. 

   Answer: B) They can only be called by the garbage collector. 

   Explanation: Finalizer methods are invoked by the garbage collector before reclaiming the memory occupied by an object, and they cannot be directly called by the programmer.