Basic Java Interview Questions



21. Question: What is the purpose of the 'interface' keyword in Java?  

   Answer: The 'interface' keyword in Java is used to declare a collection of abstract methods that can be implemented by classes. It provides a way to achieve multiple inheritances and define a contract for implementing classes.


  22. Question: How does the 'StringBuilder' class differ from 'StringBuffer' in Java?  

   Answer: Both 'StringBuilder' and 'StringBuffer' are used for string manipulation, but 'StringBuilder' is not synchronized, making it more efficient in a single-threaded environment, whereas 'StringBuffer' is synchronized, ensuring thread safety in a multi-threaded environment.


  23. Question: What is the purpose of the 'transient' keyword in Java?  

   Answer: The 'transient' keyword in Java is used to indicate that a variable should not be serialized during object serialization. It is often used for sensitive information or temporary data that doesn't need to be persisted.


  24. Question: Explain the concept of the 'superclass' and 'subclass' in Java.  

   Answer: In Java, a superclass is the class that is inherited from, and a subclass is the class that inherits from another class. The subclass inherits the attributes and behaviors of the superclass and can also have its own additional attributes and behaviors.


  25. Question: What is the purpose of the 'instanceof' operator in Java?  

   Answer: The 'instanceof' operator in Java is used to test whether an object is an instance of a particular class or interface. It returns a boolean value, indicating whether the object is of the specified type or one of its subclasses.


  26. Question: What are the differences between 'Array' and 'ArrayList' in Java?  

   Answer: An 'Array' in Java is a fixed-size data structure, while an 'ArrayList' is a dynamic array that can grow or shrink in size. 'ArrayList' provides more flexibility and additional methods, but 'Array' is generally more memory-efficient.


  27. Question: How does the 'compareTo()' method work in Java?  

   Answer: The 'compareTo()' method is used for comparing two objects in Java, typically when implementing the Comparable interface. It returns a negative value if the calling object is less than the argument, a positive value if greater, and zero if they are equal.


  28. Question: What is the purpose of the 'break' and 'continue' statements in Java?  

   Answer: The 'break' statement in Java is used to exit from a loop or switch statement prematurely, while the 'continue' statement is used to skip the rest of the code inside a loop and proceed to the next iteration.


  29. Question: Explain the concept of the 'Singleton' design pattern in Java.  

   Answer: The 'Singleton' design pattern ensures that a class has only one instance and provides a global point of access to that instance. It is often implemented by creating a private constructor, a private static instance of the class, and a public static method to retrieve that instance.


  30. Question: What is the purpose of the 'Collections' framework in Java?  

   Answer: The 'Collections' framework in Java provides a set of classes and interfaces for handling and manipulating collections of objects. It includes data structures like lists, sets, maps, and algorithms for sorting, searching, and manipulating collections.


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