In this session you will learn: How to prepare for a typical Java interview? Typical interview questions… For more information: https://www.mindsmapped.com/courses/software-development/become-a-java-developer-hands-on-training/

1. Java/J2EE Programming Training
Review Sessions

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Agenda
• How to prepare for a typical Java interview?
• Typical interview questions…

3. Interview Tips
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• 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
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• 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).

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Which package is imported implicitly by all Java programs?
The java.lang package is imported implicitly.

6. What are static blocks or static initializers?
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• 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.

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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?
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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?
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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?
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Java runtime provides a default constructor

11. Advantages of OOP?
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• Encapsulation
• Polymorphism
• Inheritance
• Abstraction

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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?
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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
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15. Difference between Method Overloading vs Overriding?
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• Please refer lecture slides

16. Difference between Comparable and Comparator interface?
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• Please refer lecture slides

17. Difference between == and equals()?
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??

18. Explain the non-final methods toString(), hashCode()
and equals() of Object class
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• Refer lecture

19. Difference between String and StringBuffer/StringBuilder
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• Please refer lecture

20. Explain the different access modifiers..
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• Public
• Private
• Default
• Protected

21. Code output?
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22. Code output?
c. Autoboxing will convert a short to a Short, but not to an Integer.
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23. Code output?
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24. Code output?
a. "j" will be converted to an Integer automatically when it is
passed to compareTo().
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25. Code output?
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26. Code output?
d. "i" will not be converted to an Integer automatically
because there is no assignment nor casting there.
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27. What is the output?
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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.
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29. True or False
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“X extends Y” is correct if and only if X is a class and Y is an interface.

30. True or False
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“X extends Y” is correct if and only if X is a class and Y is an interface.
False

31. Question
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32. Question
B and D
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33. What is the output?
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34. What is the output?
Compilation error on lines that print f.a and f.b
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35. Which of these is not correct?
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36. Which of these is not correct?
All are correct
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37. What is the output?
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38. What is the output?
Compilation error… cannot invoke countGold from
static context
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39. What is the difference between a List and a Set?
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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?
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• List, by default characteristic maintains order; a set does not.
• A set does not entertain duplicate members; whereas a List does

41. Thank You