Core Java - Interview Questions and Answers for 'Core Java' | Search Interview Question

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Q211. Can a class extend itself in Java ?

Core Java

Ans. No

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Q212. Why Concurrent Collection Classes are fail-fast in Java ?

Core Java

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Q213. What is Lock interface in Java Concurrency API ?

Core Java

Ans. Lock interface provide more extensive locking. They allow more flexible structuring and may support multiple associated Condition objects.

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Q214. What is context switching wrt Threads in Java?

Core Java

Ans. Context Switching is the process of storing and restoring of CPU state so that Thread execution can be resumed from the same point at a later point of time.

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Q215. What are the different ways to avoid multi Threading related problems in Java ?

Core Java

Ans. Synchronization,
Concurrent classes,
Volatile keyword,
Implementing concurrent Lock interface,
Immutable classes

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Q216. How does multi threading improve performance ?

Core Java

Ans. Every process in it's timeline require different resources. Utilization of resources can be optimized when they are shared among different processes or threads. When one thread is sleeping waiting for a peripheral to complete (e.g. a disk write, or a key press from the keyboard), other threads can continue using processor time and hence would lead to better usage of resources.

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Q217. Create an event class in Java.

Core Java

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Q218. Which java version supports assertion ?

Core Java

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Q219. How will you enable or disable assertion for a package during runtime ?

Core Java

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Q220. Explain Transitive equals contract.

Core Java

Ans. The equals contract is said to be transitive if

obj1.equals(obj2); and obj2(.equals(obj3)

then obj1.equals(obj3) also returns true.

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Q221. What is a reflexive equals contract ?

Core Java

Ans. An equal contract is said to be reflexive is equality between 2 objects always returns to be true.

For example -

Object o1;
Object o2;

o1.equals(o2); // returns true
o2.equals(o1); //returns true

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Q222. Which java feature is used to convert primitive type to reference type ?

Core Java

Ans. AutoBoxing

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Q223. Write code to create a folder if it doesn't exist.

Core Java

Ans. File folder = new File(path);

if(!folder.exists()){
try {
folder.mkdir();

} catch (Exception e) {}
}

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Q224. Can Java be run on hardware with just the JVM and no OS ?

Core Java

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Q225. Why do we use getbytes in Java?

Core Java

Ans. It is used to convert String into an array of bytes.

byte[] getBytes() - converts String into a byte array.

byte[] getBytes(Charset charset) - converts String to byte array, based on charset encoding.

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Q226. Have you ever used java.util.Objects class ?

Core Java

Ans. Yes, We are using requireNonNull method for validating if the object is null.

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Q227. How many VTables are there for each class ?

Core Java

Ans. There is one VTable for each class.

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Q228. How is the virtual method table implemented in Java?

Core Java

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Q229. What is virtual table with respect to method overriding in Java ?

Core Java

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Q230. Are final methods faster than regular instance methods ?

Core Java

Ans. Yes. As they cannot be overridden , there is no use of virtual table concept which is used for dynamic binding resolution.

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Q231. What could be the reasons for restricting inheritance using final class ?

Core Java

Ans. 1. Enforcing composition over inheritance
2. Restricting overriding of certain methods
3. Final methods are faster than regular instance methods
4. Enforcing Immutability

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Q232. Does use of Final class enforces composition over Inheritance in Java ?

Core Java

Ans. Yes, to a certain extent. But the objective for Final class could be beyond just enforcing composition as certain classes might have been created without inheritance or composition in mind.

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Q233. Do we have references for the objects that are eligible for garbage collection ?

Core Java

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Q234. Which memory segment is cleaned by Garbage Collection - stack or heap ?

Core Java

Ans. Heap as objects are stored ink heap.

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Q235. Why Java has final class ?

Core Java

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Q236. What is the difference between scope and access modifiers ?

Core Java

Ans. Scope modifiers changes the scope of a particular element or a method. For ex - static changes the scope of that of class and not of object.

Access modifiers changes the access priviledges of a particular element or a method. For ex - private , public etc.

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Q237. What are custom annotations and How can we create one ?

Core Java

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Q238. Can we have interface as a replacement for utility class ?

Core Java

Ans. Yes, With Java 8 we can use Interfaces as collection of utility methods through the use of default methods.

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Q239. How to sort objects based on one of the field ?

Core Java

Ans. Using comparable and comparator and sorted collections like TreeSet or TreeMap.

or

use stream api from java 8 onwards which internally refers to comparable and comparator through lambda expressions

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Q240. What does System.exit() do ?

Core Java

Ans. Generally used to indicate termination

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