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

Interview Questions and Answers - Order By Newest

Q1091. Difference between static and dynamic memory allocation ?

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Q1092. Why Arrays are considered as data structures whereas ArrayList isn't ?

Core Java

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Q1093. Are Arrays a data structure or a collection class ?

Core Java

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Q1094. Which Java version supports Interface Default methods ?

Core Java

Ans. Java 1.8 or Java 8

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Q1095. Tell something about Sleep method.

Core Java

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Q1096. Diff between Runtime.getRunTime().gc() and System.gc()

Core Java

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Q1097. How to run jar file using command prompt

Core Java

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Q1098. Can we call a static method using reference currently pointing to null.

Core Java

Ans. yes, we can.
exa: public class Java{
public static void main(String... args) {
JAva j= null;
j.greeting(); // call with null reference
}
public static void greeting() {
System.out.println("Hello World");
}
} // output: Hello World

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Q1099. Which memory segment holds the byte code ?

Core Java

Ans. Code Segment

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Q1100. Is this array declaration correct ? If not , Why ?

String[] strArray = new String[];

Core Java

Ans. No, We haven't specified the size of array to be initialized.

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Q1101. Is this array initialization correct ? If Yes, What will be the size of array ?

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

Core Java

Ans. Yes, size of the array will be 2.

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Q1102. Is this array initialization correct ? If Yes, What will be the size of array ?

String[] strArray = new String[3]{"Buggy","Bread"};

Core Java

Ans. No. It will result in error saying "Cannot define dimension expressions when an array initializer is provided"

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Q1103. Is this code valid

String[] strArray = new String[2];
strArray.length = 5;

Core Java

Ans. It will give compile time error saying "The final field array.length cannot be assigned"

Arrays once initialized cannot be resized.

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Q1104. What is the problem with this code

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

Core Java

Ans. We are trying to add an integer element to an array of String. Will give compile time error.

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Q1105. Will this give compile time error ?

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

Core Java

Ans. No. But It will throw ArrayStoreException at runtime.

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Q1106. What is TypeCasting ?

Core Java

Ans. Assigning a value of one type to a variable of another type is known as Type Casting.

Example :

int x = 10;
byte y = (byte)x;

In Java, type casting is classified into two types, Widening Casting(Implicit) widening-type-conversion and Narrowing Casting (Explicitly done) narrowing-type-conversion.

Widening or Automatic type converion - Automatic Type casting take place when,the two types are compatible and the target type is larger than the source type

Example :

public class Test {
public static void main(String[] args) {
int i = 100;
long l = i; //no explicit type casting required
float f = l;//no explicit type casting required
System.out.println("Int value " i);
System.out.println("Long value " l);
System.out.println("Float value " f);
}
}

Narrowing or Explicit type conversion - When you are assigning a larger type value to a variable of smaller type, then you need to perform explicit type casting.

Example :

public class Test{
public static void main(String[] args) {
double d = 100.04;
long l = (long)d; //explicit type casting required
int i = (int)l;//explicit type casting required
System.out.println("Double value " d);
System.out.println("Long value " l);
System.out.println("Int value " i);
}
}

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Q1107. What is the biggest Design problem in Java ?

Core Java

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Q1108. Write a java program to find the maximum profit in day trading

Core Java

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Q1109. What are basic functions of OOPS ?

Core Java

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Q1110. Where to use interface and abstract class ?

Core Java

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Q1111. Does Java SE has Immutable collections ?

Core Java

Ans. Yes wef from Java 9

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Q1112. Can you write immutable class without final?

Core Java

Ans. By making the constructor private

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Q1113. Is java fully platform independent ?

Core Java

Ans. yes, Java is a class-based and object-oriented programming language. It is a platform-independent language i.e. the compiled code can be run on any java supporting platform. It runs on the logic of “Write once, run anywhere”.

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Q1114. Can we use try within catch block ?

Core Java

Ans. Yes

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Q1115. Isnt the use of HashTable and ConcurrentHashMap the same, i.e providing synchronized map collection ?

Core Java

Ans. Both provide the thread safety but the actual difference come when talk about performance. CHM gives best performance when no of writer threads are less in number.

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Q1116. Will it print the message in Base Class constructor if we execute main method of Main class ? why ?

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

public class DerivedClass extends BaseClass{
}

public class Main {

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

Core Java

Ans. Yes.

When the Derived class constructor is initialized , a no argument super will be called intrinsically.

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Q1117. What will the following print upon executing main method of Main class ?

public class BaseClass {
BaseClass(){
System.out.println("Hello I am in Base Class 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 Constructor
Hello I am in Derived Class Constructor

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Q1118. What will the following code print upon executing main method of Main class ?

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

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

super();
}
}

public class Main {

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

Core Java

Ans. There will be compilation error within constructor of Derived Class as "super must be the first statement in constructor body".

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Q1119. What will the following code print upon executing main method of Main class ?

public class BaseClass {
BaseClass(int x){
System.out.println("Hello I am in Base Class 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. Compilation error as there is no default constructor available in BaseClass.

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Q1120. What will the following code print upon executing main method of Main class ?

public class BaseClass {
BaseClass(int x){
System.out.println("Hello I am in Base Class 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 Constructor
Hello I am in Derived Class Constructor

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