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

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Q1501. What is the difference between bubble sort using Java and C++ ?

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Q1502. What is the difference between the 'A' and "A" in Java ?

Core Java

Ans. 'A' is a character whereas "A" is a String.

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Q1503. Why is Java platform independent ?

Core Java

Ans. Platform independent language means once compiled you can execute the program on any platform (OS). Java is platform independent. Because the Java compiler converts the source code to bytecode, which is Intermediate Language. Bytecode can be executed on any platform (OS) using JVM( Java Virtual Machine).

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Q1504. What does the following code

MockitoAnnotations.initMocks(this);

Mockito

Ans. Initializes objects annotated with Mockito annotations

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Q1505. What is doCallRealMethod() method used for ?

PowerMock

Ans. When we Mock an object and then make a reference to any method using mocked object reference , java never makes a call to that method and looks for mocked value to be returned or null if none specified. But If we want that to be overridden and want java to make actual method call upon using mocked object reference, this method can be used.

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Q1506. What is the Main Advantage of the native Key Word?

Core Java

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Q1507. What is strictfp Modifier?

Core Java

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Q1508. Explain briefly about Queue Interface ?

Core Java

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Q1509. How do you convert List to Array ?

Core Java

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Q1510. Can a double value be cast to a byte ?

Core Java

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Q1511. what is volatile and atomic

Core Java

Ans. When you declare a member/variable as volatile, you are forcing threads to read values from main memory instead of thread memory.

When you declare as atomic, the read and update/write operations are performed as a single unit. A lock is acquired during atomic operation.

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Q1512. How many read and write operations are provided at the same time by ConcurrentHashMaps ?

Core Java

Ans. ConcurrentHashMaps provide unlimited read operation fro multi threaded environment. For write operation only one thread can change value for particular segment of map.

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Q1513. in the following class:
class A {
void methoda(Object o) {
Sysout("Object");
}

void methoda(String s) {
Sysout("String");
}

public static void main(String []args) {
A a = new A();
a.methoda(null);
}
}

what will be printed?

Core Java

Ans. String

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Q1514. Explain servlet lifecycle

Java EE

Ans. Init -> service -> destroy.

Out of these, init and destroy are called once per servlet whereas service is called every time when a request is made to the servlet.

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Q1515. Can we create object in static block ?

Core Java

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Q1516. What are the different ways to create objects in Java ?

Core Java

Ans. 1. Using new operator
3. Using Class.forName or Reflection
4. Using clone
5. Using Deserialization

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Q1517. What will happen if there are no enums in Java ?

Core Java

Ans. Enums in Java is a facility to have objects upfront and use them as constants. Even if such a facility is not available , a workaround could be achieved.

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Q1518. What will happen if there are no collections in java ?

Core Java

Ans. Collections in Java is nothing but a library implementation for data structures and algorithm. If it's not available , we might have to include some other library or provide our own implementation.

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Q1519. What is input Stream ?

Core Java

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Q1520. Can we serialize objects with only private variables in Java ?

Core Java

Ans. It depends on how we are serializing. The Serialization API doesn't worry about private variables and convert it into binary representation.

If we are using a library to map it to JSON / XML using XML Mappers, it may create trouble.

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Q1521. Difference between "extend" and "implement" in java?

Core Java

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Q1522. Difference between String constant and String non-constant pools?

Core Java

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Q1523. If you override hashcode to always return true, how a hash based collection will behave?

Core Java

Ans. At that bucket, it will form a linked list depending on what equals method evaluates for that object.

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Q1524. Difference between List and ArrayList ?

Core Java

Ans. List is an interface whereas ArrayList is an implementation of List.

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Q1525. Explain difference between web-based application and Core Java Application ?

Java

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Q1526. What is a base class ? Is Abstract class and Base class the same thing ?

Core Java

Ans. Base Class is a relative term. For example - Class Vehicle is a Base class of Class Car. Even though Base class is derived in this case , there is no restriction on instantiation of Vehicle class.

Abstract Class is a class that is meant only to be a Base Class and not allowed to be instantiated.

Abstract Class is a Base Class that isn't allowed to be instantiated and is only meant for carrying definition to derived class and help participate in runtime polymorphism.

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Q1527. What is the relationship between Base Class and Abstract Class ?

Core Java

Ans. Abstract Class is a class that's only allowed to be a Base class for it's usage. It can never be instantiated on it's own.

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Q1528. Can an abstract class be a derived class ?

Core Java

Ans. Yes, an abstract class can extend another class.

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Q1529. Can a method return more than one value at a time in Java ?

Core Java

Ans. object / native type returned can only be one but an object can comprise of a array , collection or a group of different value types.

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Q1530. What is the default size of list ? How it is growable ?

Core Java

Ans. Default size is 10.
Regard how size will increase.

Inside add() method there is one method called ensureCapacity() which will check list has enough size available.

This ensureCapacity() method if found size of list need to increase then it will call grow() method which will create new list of extra size and copy existing list data to new one and return.

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