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

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Q1121. Why line 4 in this code gives error saying "Cannot be referenced from a static context" ?

public class OuterClass {

public static void main(String[] args){
InnerClass innerClass = new InnerClass();
}

class InnerClass {

}
}

Core Java

Ans. InnerClass is a non static inner class and hence can only be instantiated using instance of the outer class.

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Q1122. What will the following code print upon executing main method of Main class

public class BaseClass {

BaseClass(){
this(2);
System.out.println("Hello I am in Base Class Constructor");
}

BaseClass(int i){
System.out.println("Hello I am in Base Class int argument Constructor");
}
}

public class DerivedClass extends BaseClass{
DerivedClass(){
super(1);
System.out.println("Hello I am in Derived Class Constructor");
}
}

public class Main {

public static void main(String[] args) {
DerivedClass derivedClass = new DerivedClass();
}
}

Core Java

Ans. Hello I am in Base Class int argument Constructor
Hello I am in Base Class Constructor
Hello I am in Derived Class Constructor

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Q1123. What will the following code print upon executing main method of Main class

public class BaseClass {

BaseClass(){
this(2);
System.out.println("Hello I am in Base Class Constructor");
}

BaseClass(int i){
System.out.println("Hello I am in Base Class int argument Constructor");
}
}

public class DerivedClass extends BaseClass{
DerivedClass(){
System.out.println("Hello I am in Derived Class Constructor");
}
}

public class Main {

public static void main(String[] args) {
DerivedClass derivedClass = new DerivedClass();
}
}

Core Java

Ans. Hello I am in Base Class int argument Constructor
Hello I am in Base Class Constructor
Hello I am in Derived Class Constructor

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Q1124. Why string pool concept has been introduced in string ?

Core Java

Ans. Memory Sharing and Optimal memory utilization.

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Q1125. How can we check class file format in java ?

Core Java

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Q1126. What is the use of final String when Strings are immutable ?

Core Java

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Q1127. Define Collection

Core Java

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Q1128. Does Hashtable in Java use stack operation ?

Core Java

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Q1129. 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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Q1130. 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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Q1131. What is the Main Advantage of the native Key Word?

Core Java

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Q1132. What is strictfp Modifier?

Core Java

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Q1133. Explain briefly about Queue Interface ?

Core Java

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Q1134. How do you convert List to Array ?

Core Java

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Q1135. Can a double value be cast to a byte ?

Core Java

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Q1136. 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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Q1137. 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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Q1138. 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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Q1139. Can we create object in static block ?

Core Java

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Q1140. 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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Q1141. 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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Q1142. 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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Q1143. What is input Stream ?

Core Java

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Q1144. 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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Q1145. Difference between "extend" and "implement" in java?

Core Java

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Q1146. Difference between String constant and String non-constant pools?

Core Java

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Q1147. 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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Q1148. Difference between List and ArrayList ?

Core Java

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

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Q1149. 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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Q1150. 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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