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

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Q181. Tell something about Sleep method.

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Q182. Which Java version supports Interface Default methods ?

Core Java

Ans. Java 1.8 or Java 8

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Q183. Are Arrays a data structure or a collection class ?

Core Java

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Q184. Why Arrays are considered as data structures whereas ArrayList isn't ?

Core Java

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Q185. Difference between static and dynamic memory allocation ?

Core Java

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Q186. How is it possible to use concat on string objects in Java, based on the fact that string is immutable?

Core Java

Ans. It's possible because internally java first reserves the memory for the new concatenated string and then copy that over. So after concatenation, there are 2 strings in memory, the original one and the concatenated one and then the reference is moved to the concatenated string.

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Q187. How do you implement 'state and behavior' of object in Java program?

Core Java

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Q188. Can we make array volatile in Java ?

Core Java

Ans. Yes, you can make an array (both primitive and reference type array e.g. an int array and String array) volatile in Java but only changes to reference pointing to an array will be visible to all threads, not the whole array

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Q189. Can we have 3 dimensional arrays in Java ?

Core Java

Ans. Yes

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Q190. Can we declare an array without assigning the size of an array?

Core Java

Ans. No, It will throw compile time error saying "must provide either dimension expressions or an array initializer"

Alternatively we can provide array initializer like

String[] strArray = new String[]{"Buggy","Bread"};

which will initialize it to size 2 with values as "Buggy" and "Bread"

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Q191. Write code to serialize and deserialize an array of strings ?

Core Java

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Q192. Difference between Arrays and ArrayList ?

Core Java

Ans. Both Arrays and ArrayLists are used to store elements. Elements can be either primitives or objects in case of Arrays, but only objects can be stored in Arraylist. Array is a fixed length data structure while arraylist is variable length collection class. Once created, you cannot change the size of the arrays, but arraylists can dynamically resize itself when needed.Another notable difference between Arrays and Arrayslist is that arary is part of core java programming and array list is part of collection classes

Sample Code for arrays arraylist

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Q193. What is the time and space complexity for different operations for arrays ?

Core Java

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Q194. Are arrays Thread Safe ?

Core Java

Ans. Yes

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Q195. How can we check equality for Arrays in Java ?

Core Java

Ans. You call the method java.util.Arrays.equals(Object[] a, Object[] a2)?

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Q196. Are Arrays treated like primitives or like objects in Java ?

Core Java

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Q197. Where are arrays stored in memory - stack or heap ?

Core Java

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Q198. What are jagged arrays ?

Core Java

Ans. an array of different sizes

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Q199. What is an anonymous array in Java ?

Core Java

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Q200. What is ArrayStoreException ?

Core Java

Ans. It's an exception that is thrown when we attempt to add value of an incompatible type to an array.

For example -

Object[] strArray = new String[2];
strArray[0] = 5;

In this code, strArray reference of type Object has currently been assigned the String array but at line 2 we are trying to add an integer value.

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Q201. What is the difference between ArrayIndexOutOfBoundException and ArrayStoreException?

Core Java

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Q202. Can we use generics with arrays in Java ?

Core Java

Ans. No

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Q203. Can we change the size of array once created ?

Core Java

Ans. No. Arrays cannot resize dynamically.

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Q204. How arrays work internally ?

Core Java

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Q205. Does Java generate .class file for interfaces ?

Core Java

Ans. Yes

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Q206. Can we declare an Interface with abstract keyword ?

Core Java

Ans. Yes

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Q207. Can we declare constructor inside an interface ? Why ?

Core Java

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Q208. Can we override a non-static method as static in Java ?

Core Java

Ans. No, there is no method overriding with static methods.

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Q209. Can you prevent overriding a method without using final modifier or without declaring it private ?

Core Java

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Q210. What is method hiding in Java ?

Core Java

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