Mastering Java Concepts

What are the four main principles of Object-Oriented Programming?

• Inheritance, Composition, Encapsulation, Serialization

• Polymorphism, Abstraction, Data Hiding, Class

• Encapsulation, Abstraction, Inheritance, Polymorphism

• Composition, Aggregation, Delegation, Interface

Explain the concept of inheritance in Java.

• Inheritance in Java is used to delete properties from a class.

• Inheritance in Java allows a class to inherit properties and behaviors (methods) from another class, promoting code reuse and establishing a hierarchical relationship.

• Inheritance in Java is a way to create multiple classes with no relationship.

• Inheritance allows a class to override all methods of its parent class without restrictions.

What is polymorphism and how is it implemented in Java?

• Polymorphism is only achieved through inheritance in Java.

• Polymorphism can only be implemented using abstract classes in Java.

• Polymorphism is a feature exclusive to C++ and not applicable in Java.

• Polymorphism in Java is implemented through method overriding and interfaces.

Define encapsulation and provide an example in Java.

• class Person { private String name; public String getName() { return null; } }

• class Person { public String name; }

• class Person { private String name; public void displayName() { System.out.println(name); } }

• Example in Java: class Person { private String name; public String getName() { return name; } public void setName(String name) { this.name = name; } }

What is an interface in Java and how does it differ from an abstract class?

• An interface defines a contract for classes to implement, while an abstract class can provide some method implementations and state.

• An interface can have instance variables, while an abstract class cannot.

• An interface is a type of class that cannot be instantiated, while an abstract class can be instantiated.

• An interface can only contain static methods, while an abstract class can contain instance methods.

How do you handle exceptions in Java?

• Use if-else statements to handle exceptions in Java.

• Throw exceptions without handling them.

• Use try-catch blocks to handle exceptions in Java.

• Ignore exceptions and continue execution.

What is the purpose of the try-catch block in Java?

• To optimize memory usage.

• To improve code readability.

• To define variables in a method.

• To handle exceptions and prevent program crashes.

What is the difference between checked and unchecked exceptions?

• Checked exceptions are always runtime errors.

• Both checked and unchecked exceptions require handling.

• Checked exceptions require handling, while unchecked exceptions do not.

• Unchecked exceptions must be declared in the method signature.

Explain the use of the finally block in exception handling.

• The 'finally' block is optional and does not affect program execution.

• The 'finally' block can only be used with a try block that has no catch.

• The 'finally' block guarantees execution of code after try/catch, for cleanup actions.

• The 'finally' block is used to catch exceptions before they propagate.

What is the Java Collections Framework?

• A framework for building graphical user interfaces in Java.

• A unified architecture for representing and manipulating collections of objects in Java.

• A library for network programming in Java.

• A set of tools for database management in Java.