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

Interview Questions and Answers - Order By Newest

Q821. Write a Program to find age by birth date ?

Ans. LocalDate today = LocalDate.now();
LocalDate birthday = LocalDate.of(1960, Month.JANUARY, 1);
Period p = Period.between(birthday, today); //Now access the values as below
System.out.println(period.getDays());
System.out.println(period.getMonths());
System.out.println(period.getYears());

Sample Code for LocalDate

Sample Code for Period

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve coding code date LocalDate Period Asked in 1 Companies}

Q822. Explain Inheritance and Polymorphism.

Core Java

Ans. Getting parent class object properties into child class is called Inheritance.

The process of representing one form into multiple forms is called polymorphism.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve inheritance object oriented programming (oops) oops concepts polymorphism object oriented programming (oops) oops concepts Asked in 1 Companies Basic frequent}

Q823. What will be the output of following code

class TestMain {
public static void main(String[] args) {
String s1 = "ravi";
String s2 = new String("ravi");
Integer i = 10;
Integer a1 = new Integer("10");
System.out.println(s1 == s1);
System.out.println(i == a1);
}
}

Core Java

Ans. false
false

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve object equality == coding code Asked in 1 Companies}

Q824. Will the following code compile ?

final HashMap hm = new HashMap();
hm.put("Ravi", 221);

Core Java

Ans. Yes, it will compile without error. final in this context means that the reference hm cannot be assigned to a new hash map but didn't restrict from changing the state of collection already held by hm.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve final final variable Asked in 1 Companies}

Q825. Explain Java 8 concurrency mechanism.

Core Java

^{This question was recently asked at 'IBM'.This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve synchronization concurrency java 8 java8 Asked in 1 Companies}

Q826. What is the difference between being final and being immutable ? Are string final or immutable in Java ?

Core Java

Ans. Being final in the sense of objects or object reference means that the reference cannot be reassigned to a different object whereas being immutable means that the object contents cannot be changed.

Strings in Java are immutable.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve string immutable immutability final vs immutable immutability}

Q827. What does the following initialization mean ?

ArrayList<LinkedList> traversalPaths = new ArrayList<LinkedList>();

What could be the use of such a collection.

Core Java

Ans. Initialize an ArrayList that will hold LinkedLists i.e every element of the arraylist will be a linked list.

Such collection could be used in algorithms that require first random access and then sequential traversal. For example - Storing traversal paths for a graph wherein we can start from any vertex. Implementing dictionary with each arraylist element holding staring with character and then linked list holding duplicate words.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve collections linkedlist arraylist}

Q828. What will be the output upon executing main method

public class Graph {
   private static Multimap<Integer,Integer> adjacentDirectedNodesMap = ArrayListMultimap.create();

   Graph(){
      adjacentDirectedNodesMap.put(1, 2);
      adjacentDirectedNodesMap.put(1, 3);
      adjacentDirectedNodesMap.put(1, 4);
      adjacentDirectedNodesMap.put(3, 5);
      adjacentDirectedNodesMap.put(4, 5);
   }

   public static void main(String[] args){
      ArrayList visited = new ArrayList();

      Integer startNode = 1;

      for(Integer adjacentNodes: adjacentDirectedNodesMap.get(startNode)){
            System.out.println(adjacentNodes);
      }
   }
}

Core Java

Ans. Nothing as we haven't yet created an instance and hence adjacentDirectedNodesMap won't be initialized with any value and hence is empty.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve constructor}

Q829. What is the difference between return and continue statement ?

Core Java

Ans. return is used within a method to return control out of the method. It may be followed by a value which is returned from the method to calling method immediately preceding the point of call.

continue statement is used within a loop to start next iteration without executing the remaining statements in the loop.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve return statement continue statement return vs continue for loop control statements loop statement}

Q830. What is the difference between return and break statement ?

Core Java

Ans. return is used within a method to return control out of the method. It may be followed by a value which is returned from the method to calling method immediately preceding the point of call.

break statement is used within a loop to move control out of the loop.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve return statement break statement return vs break}

Q831. What is the difference between Java SE Map and Apache Commons MultiMap ? How can we implement functionality similar to multimap using Java SE map ?

Core Java

Ans. We can have duplicate keys within MultiMap whereas we cannot have duplicate keys within Java Util Map.

We can have a Map with value as a "collection of values" instead of single value to have a similar function as Multimap.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Apache commons multimap map vs multimap}

Q832. What is the difference between hasNextInt and nextInt method of scanner class ?

Core Java

Ans. The hasNextInt() is used to check if there are any more elements left and the nextInt() is used to access that element.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve input output Scanner}

Q833. Is it a bad practice to initialize object reference to Null ?

Core Java

Ans. never initialise local to null,yes it is bad pratice

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve null nullpointerexception}

Q834. What will be the output of following code and Why ?

int x = 5;
int y = 7;
float f = 5f;
float z = y / x * f;
System.out.println(z);

Core Java

Ans. 5.0

operation between two ints generate int only. so 7/5 generates 1 and not 1.4. Multiplication between int and float generates float and hence

1 * 5.0 = 5.0

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve arithmetic calculation data types}

Q835. How do you know if a method is a constructor ?

Core Java

Ans. Is the method name same as class Name - Yes

Does the method have any return type ( even void ) - No

It's a constructor

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve constructor}

Q836. Is a string an array of characters in Java ?

Core Java

Ans. No, String is a class whose objects are called strings in Java.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve String}

Q837. Can we synchronize the run() method in Java?

Core Java

^{This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve synchronization multithreading run method}

Q838. Difference between if and switch ? Can we replace all switch statements with if statements ?

Core Java

Ans. if statement is used to do 2 direction branching whereas switch is used to do multi direction branching in Java.

Yes we can replace all switch statements with nested if statements.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve switch if vs switch}

Q839. What is nested if ?

Core Java

Ans. if statements nested within another if or else blocks are called nested if statements.

if(condition1) {
if(condition2){
}
}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve if statement control statements nested if}

Q840. Write a Program to check if the entered number is a Duck Number ( Number having 0 in it ) ?

Core Java

^{This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve code coding duck number}

Q841. What will the following code print ?

int x[] = new int[5];
x[0] = 1;
x[1] = 2;

for(int count=0;count<x.length;count++){
System.out.println(x[count]);
}

Core Java

Ans. 1
2
0
0
0

As arrays are not dynamically expanded , we have declared the array for size 10. As we have only initialized only 2 values , it will print rest as their default values.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve arrays}

Q842. What will the following code print

int x[] = new int[5];
x[0] = 1;
x[1] = 2;

for(int count=0;count<=x.length;count++){
System.out.println(x[count]);
}

Core Java

Ans. 1
2
0
0
0
ArrayIndexOutOfBoundException: 5

As array index starts with 0 and ends with the index of (size - 1), the index 5 is inaccessible for the array and hence will throw the exception.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve arrays}

Q843. what are different pointer operators used ?

Core Java

^{This question was recently asked at 'Huawei Technologies'.This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q844. What is mutable in Java ?

Core Java

^{This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve}

Q845. Which java features makes java different from other languages ?

Core Java

^{This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve}

Q846. Why cant we start an identifier with a number in Java?

Core Java

^{This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve}

Q847. What is the default data type of Serialized methods?'

Core Java

^{This question was recently asked at 'Intime Tec'.This question is still unanswered. Can you please provide an answer.}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q848. Do we have a method to reverse a string in String class ?

Core Java

Ans. No but we have it in StringBuilder.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve String StringBuilder Reverse a string}

Q849. How can we convert char into a String ?

Core Java

Ans. We can use StringBuilder. StringBuilder accepts char as the argument for it's constructor.

new StringBuilder('').toString();

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve convert char to String char String}

Q850. How can we check if a particular character is upper case in Java ?

Core Java

Ans. 1. We can compare the ascii value of the character. Ascii for Capital case character is from 65 to 90.

2. We can compare to see if lowerCase of the character is not equal to character itself.

For example -

if character is 'a' the following code

new StringBuilder(char).toString().toLowerCase().equals(new StringBuilder(char)

will return true and hence char is lower case

if character is 'A' the following code

new StringBuilder(char).toString().toLowerCase().equals(new StringBuilder(char)

will return false and hence char is upper case

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve check upper case character character}

Search Interview Questions

Help us and Others Improve. Please let us know the questions asked in any of your previous interview.