Review Session and Attending Java Interviews
- 1. Java/J2EE Programming Training Review Sessions
- 2. Page 2Classification: Restricted Agenda • How to prepare for a typical Java interview? • Typical interview questions…
- 3. Interview Tips Classification: Restricted Page 2 • How to prepare for a typical Java interview? • Typical interview questions…
- 4. Give few reasons for using Java / Advantages of Java over other programming languages Classification: Restricted Page 3 • Built-in support for multi-threading, socket communication, and memory management (automatic garbage collection). • Object Oriented (OO). • Better portability than other languages across operating systems • Supports Web based applications (Applet, Servlet, and JSP), distributed applications (sockets, RMI, EJB etc.) and network protocols (HTTP, JRMP etc) with the help of extensive standardized APIs (Application Programming Interfaces).
- 5. Classification: Restricted Page 4 Which package is imported implicitly by all Java programs? The java.lang package is imported implicitly.
- 6. What are static blocks or static initializers? Classification: Restricted Page 5 • When a class is loaded, all blocks that are declared static and don’t have function name (i.e. static initializers) are executed even before the constructors are executed. As the name suggests they are typically used to initialize static fields.
- 7. Classification: Restricted Page 6 Difference between constructors and other regular methods? • Constructors must have the same name as the class name and cannot return a value. • The constructors are called only once per creation of an object while regular methods can be called many times
- 8. Can you call one constructor from another? Classification: Restricted Page 7 Yes, by using this() public Pet(int id) { this.id = id; // “this” means this object } public Pet (int id, String type) { this(id); // calls constructor public Pet(int id) this.type = type; // ”this” means this object }
- 9. How to call superclass constructor? Classification: Restricted Page 8 By using super keyword public SpecialPet(int id) { super(id); //must be the very first statement in the constructor. } You can also use super.myMethod() to call the superclass’s myMethod. This can be called at any line.
- 10. What happens if you do not provide a constructor? Classification: Restricted Page 9 Java runtime provides a default constructor
- 11. Advantages of OOP? Classification: Restricted Page 10 • Encapsulation • Polymorphism • Inheritance • Abstraction
- 12. Classification: Restricted Page 11 Difference between inheritance and composition/aggregation? • The ‘is a’ relationship is expressed with inheritance and ‘has a’ relationship is expressed with composition. Both inheritance and composition allow you to place sub-objects inside your new class. Two of the main techniques for code reuse are class inheritance and object composition • Example: ScienceStudent is a Student; Student has an Address.
- 13. Difference between abstract class and interface? Classification: Restricted Page 12 Refer previous session slides • Abstract classes have executable methods and abstract methods. Interfaces have no implementation code. All methods are abstract. • One class can only subclass one abstract class. A class can implement any number of interfaces
- 14. Why multiple inheritance is not allowed? • Diamond problem Classification: Restricted Page 13
- 15. Difference between Method Overloading vs Overriding? Classification: Restricted Page 14 • Please refer lecture slides
- 16. Difference between Comparable and Comparator interface? Classification: Restricted Page 15 • Please refer lecture slides
- 17. Difference between == and equals()? Classification: Restricted Page 16 ??
- 18. Explain the non-final methods toString(), hashCode() and equals() of Object class Classification: Restricted Page 17 • Refer lecture
- 19. Difference between String and StringBuffer/StringBuilder Classification: Restricted Page 18 • Please refer lecture
- 20. Explain the different access modifiers.. Classification: Restricted Page 19 • Public • Private • Default • Protected
- 21. Code output? Classification: Restricted Page 20
- 22. Code output? c. Autoboxing will convert a short to a Short, but not to an Integer. Classification: Restricted Page 21
- 23. Code output? Classification: Restricted Page 22
- 24. Code output? a. "j" will be converted to an Integer automatically when it is passed to compareTo(). Classification: Restricted Page 23
- 25. Code output? Classification: Restricted Page 24
- 26. Code output? d. "i" will not be converted to an Integer automatically because there is no assignment nor casting there. Classification: Restricted Page 25
- 27. What is the output? Classification: Restricted Page 26
- 28. What is the output? It will print “a”. The g() in Bar is not overriding the g() in Foo. It is just overloading the name "g". When determining which method to call, autoboxing is not considered first so only the g() in Foo is applicable and thus is used. Classification: Restricted Page 27
- 29. True or False Classification: Restricted Page 28 “X extends Y” is correct if and only if X is a class and Y is an interface.
- 30. True or False Classification: Restricted Page 29 “X extends Y” is correct if and only if X is a class and Y is an interface. False
- 32. Question B and D Classification: Restricted Page 31
- 33. What is the output? Classification: Restricted Page 32
- 34. What is the output? Compilation error on lines that print f.a and f.b Classification: Restricted Page 33
- 35. Which of these is not correct? Classification: Restricted Page 34
- 36. Which of these is not correct? All are correct Classification: Restricted Page 35
- 37. What is the output? Classification: Restricted Page 36
- 38. What is the output? Compilation error… cannot invoke countGold from static context Classification: Restricted Page 37
- 39. What is the difference between a List and a Set? Classification: Restricted Page 38 Set: HashSet: Default Set …must implement equals and hashCode LinkedHashSet: Maintains the elements in the order in which they were entered TreeSet: Maintains in ascending order/sorted TreeSet<Student> ts = new TreeSet<Student>(); Comparable: Default comparison logic…. Student implements Comparable… override compareTo() Comparator: Multiple Comparator classes by implementing Comparator and overriding compare()
- 40. What is the difference between a List and a Set? Classification: Restricted Page 39 • List, by default characteristic maintains order; a set does not. • A set does not entertain duplicate members; whereas a List does
- 41. Thank You