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

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Q251. What is a reflexive equals contract ?

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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Q252. Which java feature is used to convert primitive type to reference type ?

Core Java

Ans. AutoBoxing

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Q253. 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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Q254. Can Java be run on hardware with just the JVM and no OS ?

Core Java

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Q255. 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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Q256. 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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Q257. How many VTables are there for each class ?

Core Java

Ans. There is one VTable for each class.

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Q258. How is the virtual method table implemented in Java?

Core Java

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Q259. What is virtual table with respect to method overriding in Java ?

Core Java

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Q260. 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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Q261. 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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Q262. 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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Q263. Do we have references for the objects that are eligible for garbage collection ?

Core Java

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Q264. 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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Q265. Why Java has final class ?

Core Java

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Q266. 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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Q267. What are custom annotations and How can we create one ?

Core Java

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Q268. 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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Q269. 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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Q270. What does System.exit() do ?

Core Java

Ans. Generally used to indicate termination

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Q271. Write code to print a Pyramid pattern ?

Core Java

Ans. public static void printTriagle(int n)
{
// outer loop to handle number of rows
// n in this case
for (int i=0; i1; j--)
{
// printing spaces
System.out.print(" ");
}

// inner loop to handle number of columns
// values changing acc. to outer loop
for (int j=0; j<=i; j )
{
// printing stars
System.out.print("* ");
}

// ending line after each row
System.out.println();
}
}

// Driver Function
public static void main(String args[])
{
int n = 5;
printTriagle(n);
}

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Q272. Can we have multiple inheritance in java using abstract class ?

Core Java

Ans. No

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Q273. What is the difference between abstraction and abstract class ?

Core Java

Ans. Abstract class is one of the facility for achieving abstraction in Java.

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Q274. Difference between == and === ?

JavaScript

Ans. == compares values === is used in scripting languages for comparing two values as well as there data tpe. like in js,php.

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Q275. How to calculate string length without using inbuilt function

Core Java

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Q276. What is the following code doing ?

private static final String[] COLORS = new String[] { "Red", "Green", "Blue" };

Core Java

Ans. We are initializing a static and constant string array named as COLORS using Strings "Red","Green" and "Blue".

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Q277. Have you used Java 8 Lambda expressions ?

Core Java

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Q278. Write a Program to print a pattern ?

Core Java

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Q279. Which of the following is insertion heavy - HashSet or TreeSet ?

Core Java

Ans. TreeSet as it needs elements in a particular order

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Q280. What is the difference between TreeSet and TreeMap ?

Core Java

Ans. TreeSet contains only values as elements whereas TreeMap contains Key value pairs.

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