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

Interview Questions and Answers - Order By Newest

Q31. What will be the output of following code ?

public static void main(String[] args){
String child = null;
File file = new File("/folder", child);
try {
file.createNewFile();
} catch (IOException e) {
e.printStackTrace();
}
}

Core Java

Ans. NullPointerException at line:File file = new File("/folder", child);

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Q32. What will be the output of following code, assuming that currently we are in c:Project ?

public static void main(String[] args){
String child = null;
File file = new File("../file.txt");
System.out.println(file.getPath());
System.out.println(file.getAbsolutePath());
try {
System.out.println(file.getCanonicalPath());
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

Core Java

Ans. ..file.txt
C:WorkspaceProject..file.txt
C:Workspacefile.txt

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Q33. Which of the following code is correct ?

a.

FileWriter fileWriter = new FileWriter("../file.txt");
File file = new File(fileWriter );
BufferedWriter bufferedOutputWriter = new BufferedWriter(fileWriter);

b.

BufferedWriter bufferedOutputWriter = new BufferedWriter("../file.txt");
File file = new File(bufferedOutputWriter );
FileWriter fileWriter = new FileWriter(file);

c.

File file = new File("../file.txt");
FileWriter fileWriter = new FileWriter(file);
BufferedWriter bufferedOutputWriter = new BufferedWriter(fileWriter);

d.

File file = new File("../file.txt");
BufferedWriter bufferedOutputWriter = new BufferedWriter(file);
FileWriter fileWriter = new FileWriter(bufferedOutputWriter );

Core Java

Ans. c.

File file = new File("../file.txt");
FileWriter fileWriter = new FileWriter(file);
BufferedWriter bufferedOutputWriter = new BufferedWriter(fileWriter);

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Q34. Which exception should be handled in the following code ?

File file = new File("../file.txt");
FileWriter fileWriter = new FileWriter(file);

Core Java

Ans. IOException

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Q35. Which exceptions should be handled with the following code ?

FileOutputStream fileOutputStream = new FileOutputStream(new File("newFile.txt"));

Ans. FileNotFoundException

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Q36. What is the problem with this code ?

class BuggyBread1 {

private BuggyBread2 buggybread2;

public static void main(String[] args){
try {
BuggyBread1 buggybread1 = new BuggyBread1();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("newFile.txt")));
objectOutputStream.writeObject(buggybread1);
} catch (Exception e) {
e.printStackTrace();
}
}
}

Core Java

Ans. Though we are trying to serialize BuggyBread1 object but we haven't declared the class to implement Serializable.

This will throw java.io.NotSerializableException upon execution.

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Q37. Will this code run fine if BuggyBread2 doesn't implement Serializable interface ?

class BuggyBread1 implements Serializable{
private BuggyBread2 buggybread2 = new BuggyBread2();

public static void main(String[] args){
try {
BuggyBread1 buggybread1 = new BuggyBread1();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("newFile.txt")));
objectOutputStream.writeObject(buggybread1);
} catch (Exception e) {
e.printStackTrace();
}
}
}

Core Java

Ans. No, It will throw java.io.NotSerializableException.

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Q38. Will this code work fine if BuggyBread2 doesn't implement Serializable ?

class BuggyBread1 extends BuggyBread2 implements Serializable{
private int x = 5;

public static void main(String[] args){
try {
BuggyBread1 buggybread1 = new BuggyBread1();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("newFile.txt")));
objectOutputStream.writeObject(buggybread1);
} catch (Exception e) {
e.printStackTrace();
}
}
}

Core Java

Ans. Yes.

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Q39. What will the following code print ?

java.util.Calendar c = java.util.Calendar.getInstance();
c.add(Calendar.MONTH, 5);
System.out.println(c.getTime());

Core Java

Ans. Date and Time after 5 months from now.

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Q40. Write a program to see if the number is perfect number or not ?

Core Java

Ans. http://www.c4learn.com/c-programs/program-to-check-whether-number-is.html

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Q41. What will be the output of this code ?

Set mySet = new TreeSet();
mySet.add("4567");
mySet.add("5678");
mySet.add("6789");
for(String s: mySet){
System.out.println(s);
}

Ans. 4567
5678
6789

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Q42. public enum Day {
SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
THURSDAY, FRIDAY, SATURDAY
}

public class Test {
Set mySet = new HashSet();
mySet.add(Day.MONDAY);
mySet.add(Day.SUNDAY);
mySet.add(Day.SATURDAY);

for(Day d: mySet){
System.out.println(d);
}
}

Ans. SUNDAY
MONDAY
SATURDAY

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Try 3 Question(s) Test

Q43. What will be the output of the following code ?

enum Day {
   MONDAY,TUESDAY,WEDNESDAY,THURSDAY,FRIDAY,SATURDAY,SUNDAY
}

public class BuggyBread1{
   public static void main (String args[]) {
      Set mySet = new HashSet();
      mySet.add(Day.SATURDAY);
      mySet.add(Day.WEDNESDAY);
      mySet.add(Day.FRIDAY);
      mySet.add(Day.WEDNESDAY);
      for(Day d: mySet){
         System.out.println(d);
      }
   }
}

Ans. FRIDAY , SATURDAY and WEDNESDAY will be printed but the order cannot be determined.

Only one FRIDAY will be printed as Set doesn't allow duplicates. Order cannot be determined as HashSet doesn't maintain elements in a particular order.

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Try 3 Question(s) Test

Q44. public class BuggyBread1{

public static void main (String args[]) {
Set<String> mySet = new TreeSet<String>();
mySet.add(""1"");
mySet.add(""2"");
mySet.add(""111"");
for(String d: mySet){
System.out.println(d);
}
}
}

Core Java

Ans. 1
111
2

TreeSet maintains the elements in the ascending order which is identified by the compareTo method. compareTo method in String has been defined such that it results in the natural alphabetic Order. Here the elements in the TreeSet are of String and not of Integer. In String Natural Order, 111 comes before 2 as ascii of 1st character first determines the order.

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Q45. public class BuggyBread1{

public static void main (String args[]) {
Set<Integer> mySet = new TreeSet<Integer>();
mySet.add(1);
mySet.add(2);
mySet.add(111);
for(Integer d: mySet){
System.out.println(d);
}
}
}

Core Java

Ans. 1
2
111

TreeSet maintains the elements in the ascending order which is identified by the compareTo method. compareTo method in Integer has been defined such that it results in the natural numerical Order.

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Q46. Will this Code compile ?

abstract public class BuggyBread1{
abstract public void test(){};
}

Core Java

Ans. No. This will give a compilation error saying "Abstract methods do not specify a body".

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Q47. Write program for input: I am a boy, output: I1 am2 a1 boy3?

Ans. public static void main (String args[]) {
String inputStr = "I am a boy, output: I1 am2 a1 boy3";

String splitStr[] = inputStr.split(" ");

String outputStr = new String();

for(String str1: splitStr){
outputStr += str1 + str1.length() + " ";
}

System.out.println(outputStr);
}

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Q48. What is the difference between out.println(a+b); and out.println (a+" " +b); in Java? with a=2 and b=1

Core Java

Ans. First will give the ouput as 3 and the second will give output as 2 1

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Q49. How many elements will be there in TreeSet after the last line and Why ?

TreeSet set = new TreeSet();
set .add(new String("abc"));
set .add(new String("abc"));

Core Java

Ans. One.

As we haven't specified the type of TreeSet, it being evaluated with the first element insertion. Once it's identified that it's of type String and as no comparator has been defined, the comparison is done using the String compareTo method. String compareTo method compares the elements by the content / value.

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Q50. What will the following code result ?

List> intList = new ArrayList>();

intList.add(Optional.empty());
intList.add(Optional.of(2));
intList.add(Optional.of(3));
intList.add(Optional.of(4));

System.out.println(intList.get(null));

Ans. Compile time error at last line as the get method expect argument of type native int.

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Q51. What will the following code result ? Will it compile ?

List> intList = new ArrayList>();

intList.add(Optional.empty());
intList.add(Optional.of(2));
intList.add(Optional.of(3));
intList.add(Optional.of(4));

System.out.println(intList.get((Integer)null));

Ans. Yes but the last line will throw NullPointerException upon execution.

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Q52. What will be the output ?Integer a = 10, b =10;Integer c = 10, d = 1000;System.out.println(a == b);System.out.println(c ==d);

Core Java

Ans. truefalse

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Q53. How many bits are used to represent Unicode ?

a. 8 bits
b. 16 bits
c. 24 bits
d. 32 bits

Ans. 16 bits

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Q54. Print natural numbers sequentially with two threads.

Core Java

Ans. http://stackoverflow.com/questions/18799591/print-natural-sequence-with-help-of-2-threads1-is-printing-even-and-2nd-is-pri

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Q55. Find the repeating number using O(n) time and constant space.

Algorithm

Ans. http://www.geeksforgeeks.org/find-duplicates-in-on-time-and-constant-extra-space/

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Q56. Write a method to convert all elements of a set to lower case.

Core Java

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=Method+to+convert+all+elements+of+a+collection&category=code

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Q57. Write code for singleton class

Design

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=singleton+class&category=code

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Q58. Write a program / method to input few numbers and then print the sum.

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?&category=code&searchOption&keyword=946

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Very frequently asked to fresh graduates. Frequently asked in NSEiT and Accenture India

Q59. Write a program to Generate prime numbers till a given number

Core Java

Ans. public class Main {
public static void main(String args[]) {
int number = 2;
int count = 0;
long sum = 0;
int givenNumber = 1000;
while (count < givenNumber) {
if (isPrimeNumber(number)) {
sum = number;
count;
}
number;
}
System.out.println(sum);
}
private static boolean isPrimeNumber(int number) {
for (int i = 2; i <= number / 2; i) {
if (number % i == 0) {
return false;
}
}
return true;
}
}

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Q60. Write a program to calculate factorial of a number using recursion

Core Java

Ans.

public class Factorial {
   public static void main(String[] args){
      int x = 5;

      System.out.println(calculateFactorial(x));

   }

   private static int calculateFactorial(int x){
      if(x==1){
         return 1;
      }
      return x * calculateFactorial(x-1);
   }
}

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