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45 Most Common Java Software Engineer Interview Questions And Answers
Java Software Engineer based Frequently Asked Questions in various Java Software Engineer job interviews by interviewer. These professional questions are here to ensures that you offer a perfect answers posed to you. So get preparation for your new job hunting
1 Do you know how threadsafe is enum in Java?
2 Explain me what is a good usecase of calling System.gc()?
3 Explain me why doesn’t the following code generate a NullPointerException even when the instance is null?
4 Do you know what is the advantage of generic collection?
5 Tell us what do you mean by aggregation?
6 Tell me can an enum be extended?
7 Explain me when do you need to override the equals and hashCode methods in Java?
8 Tell us what are checked and unchecked exceptions? When do you use them?
9 Tell us how can you swap the values of two numeric variables without using any other variables?
10 Tell us what are constructors in Java?
11 Can you explain me what is Polymorphism?
12 Explain me what is method overloading and method overriding?
13 Explain me what is association?
14 int a = 1L; won’t compile and int b = 0; b += 1L; compiles fine. Explain me why?
15 Can you give real world examples of when to use an ArrayList and when to use LinkedList?
16 Tell us why would it be more secure to store sensitive data (such as a password, social security number, etc.) in a character array rather than in a String?
17 Explain me what is the volatile keyword? How and why would you use it?
18 Explain me what does it mean for a collection to be “backed by” another? Give an example of when this property is useful?
19 Explain me what is the difference between String s = "Test" and String s = new String("Test")? Which is better and why?
20 Explain me what is runtime polymorphism or dynamic method dispatch?
21 Tell me public static void main(String args)?
22 Tell us what is the Java Classloader? List and explain the purpose of the three types of class loaders?
23 Can you compare the sleep() and wait() methods in Java, including when and why you would use one vs. the other?
24 How to override a private or static method in Java?
25 Tell me what are static initializers and when would you use them?
26 Explain me how can you catch an exception thrown by another thread in Java?
27 As you know ArrayList, LinkedList, and Vector are all implementations of the List interface. Which of them is most efficient for adding and removing elements from the list? Explain your answer, including any other alternatives you may be aware of?
28 Explain me why aren’t you allowed to extend more than one class in Java but are allowed to implement multiple interfaces?
29 Please explain what is the ThreadLocal class? How and why would you use it?
30 Tell me what is multiple inheritance? Is it supported by Java?
31 Tell me what is reflection? Give an example of functionality that can only be implemented using reflection?
32 Tell us what is the difference between equals() and == ?
33 Tell me why is the code printing true in the second and false in the first case?
34 Please explain and compare fail-fast and fail-safe iterators. Give examples?
35 Do you know what is a Service?
36 Explain me how does the JVM handle storing local variables vs storing objects?
37 Tell us what is the marker interface in Java?
38 Tell me what is the difference between an Iterator and a ListIterator?
39 Explain me what is singleton class and how can we make a class singleton?
40 Explain me how are Annotations better than a Marker Interfaces?
41 Explain me when do you use volatile variables?
42 Do you know why Java is platform independent?
43 Explain me what is the difference between HashMap and ConcurrentHashMap?
44 Tell us why do you need to use synchronized methods or blocks?
45 Tell us why java is not 100% Object-oriented?
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