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

Core Java - Interview Questions and Answers for 'Coding' - 122 question(s) found - Order By Newest

Q1. What will this code print ?

String a = new String ("TEST");
String b = new String ("TEST");
if(a == b) {
System.out.println ("TRUE");
} else {
System.out.println ("FALSE");
}

Core Java

Ans. FALSE. == operator compares object references, a and b are references to two different objects, hence the FALSE. .equals method is used to compare string object content.

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Q2. How to find whether a given integer is odd or even without use of modulus operator in java?

Core Java

Ans. public static void main(String ar[])
{
int n=5;
if((n/2)*2==n)
{
System.out.println("Even Number ");
}
else
{
System.out.println("Odd Number ");
}
}

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Q3. What will be the output of following code ?

public static void main(String[] args){
String name = null;
File file = new File("/folder", name);
System.out.print(file.exists());
}

Core Java

Ans. NullPointerException

at line: "File file = new File("/folder", name);"

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Q4. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?

Ans. Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.

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Q5. What will be the output of following code ?

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

Core Java

Ans. It will create the file myfile.txt in the current directory.

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Q6. Trim a string without using String library method

Core Java

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

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Usually asked to entry level software developers.

Q7. Write a program to swap two variables without using third

Core Java

Ans. public static void main(String[] args) {
   int num1 = 1;
   int num2 = 2;
   num1 = num1^num2;
   num2 = num1^num2;
   num1 = num1^num2;
   System.out.print("num1 = " + num1 +", num2 = "+num2);
}

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Q8. What will be the output of following Code ?

class BuggyBread {
   public static void main(String[] args) {
      String s2 = "I am unique!";
      String s5 = "I am unique!";

      System.out.println(s2 == s5);
   }
}

Core Java

Ans. true, due to String Pool, both will point to a same String object.

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Q9. What will be the output of following code ?
class BuggyBread2 {
   private static int counter = 0;
   void BuggyBread2() {
      counter = 5;
   }

   BuggyBread2(int x){
      counter = x;
   }

   public static void main(String[] args) {
      BuggyBread2 bg = new BuggyBread2();
      System.out.println(counter);
   }
}

Core Java

Ans. Compile time error as it won't find the constructor matching BuggyBread2().
Compiler won't provide default no argument constructor as programmer has already defined one constructor.
Compiler will treat user defined BuggyBread2() as a method, as return type ( void ) has been specified for that.

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Q10. What's wrong with this code ?

public static void main(String[] args) {
String regex = "(\\w+)*";
String s = "Java is a programming language.";

Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(s);
while (matcher.next()) {
System.out.println("The e-mail id is: " + matcher.group());
}
}

Core Java

Ans. matcher.find() should have been used instead of matcher.next() within while.

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Q11. What will be the output of this code ?

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

Ans. It will print 4567,5678 and 6789 but Order cannot be predicted.

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Q12. What will be the output of this code ?

Set mySet = new HashSet();
mySet.add("4567");
mySet.add("5678");
mySet.add("6789");
System.out.println(s.get(0));

Ans. This will give compile time error as we cannot retrieve the element from a specified index using Set. Set doesn't maintain elements in any order.

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Q13. 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 TreeSet();
mySet.add(Day.SATURDAY);
mySet.add(Day.WEDNESDAY);
mySet.add(Day.FRIDAY);
mySet.add(Day.WEDNESDAY);
for(Day d: mySet){
System.out.println(d);
}
}
}

Core Java

Ans. WEDNESDAY
FRIDAY
SATURDAY

Only one FRIDAY will be printed as Set doesn't allow duplicates.Elements will be printed in the order in which constants are declared in the Enum. TreeSet maintains the elements in the ascending order which is identified by the defined compareTo method. compareTo method in Enum has been defined such that the constant declared later are greater than the constants declared prior.

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Q14. Implement the following method ?

int findMax(int[] items)

Core Java

Ans. int findMax(int[] items){
   int maxNumber = 0;
   for(int x:items){
      if(x > maxNumber){
         maxNumber = x;
      }
   }

   return maxNumber;
}

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Q15. Write a program to print all even numbers first and then all odd numbers till 100. For example the output should be
2
4
6
8
...... 100
and then
1
3
5
7
...... 99

using only 1 for loop ? Is it possible with just one loop ?

Core Java

Ans. Yes , It can be done using single for loop

public class BuggyBread{
public static void main (String args[]) {
   int x = 50;
   for(int i=1;i <= 100;i++){
      if(i<=50){
         System.out.println(i*2);
      } else {
         System.out.println(i-x);
         x = x - 1;
      }
   }
}
}

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Q16. Given two files with list of words, write a program to show the common words in both files

Core Java

Ans. import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.io.*;
public class Common {
public static void main(String ar[])throws Exception
   {
      File f=new File("a.txt");
File f1=new File("x.java");
      System.out.println(f.exists());
FileInputStream fin = new FileInputStream(f);
      FileInputStream fin1 = new FileInputStream(f1);

      byte b[]=new byte[10000];
byte b1[]=new byte[10000];
fin.read(b);
fin1.read(b1);
String s1 = new String(b);
String s2 =new String(b1);

String words1[] = s1.trim().split(" ");
String words2[] = s2.trim().split(" ");
Listlist1 = new ArrayList<>(Arrays.asList(words1));
Listlist2 = new ArrayList<>(Arrays.asList(words2));
list1.retainAll(list2);
System.out.println(list1);
}
}

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Q17. Write an algorithm / Java Program to show duplicates in an array of n elements?

Algorithm

Ans. int duplicateArray[] = { 1, 2, 2, 3, 4, 5, 6, 8, 9}
Set unique = new HashSet();
for (int i = 0; i < duplicateArray.length; i) {
if (unique.contains(duplicateArray[i])) {
System.out.println(duplicateArray[i]);
} else {
unique.add(duplicateArray[i]);
}
}

Complexity O(n) = nHashSet contains and add has O(n) = 1

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Q18. Find different combination of given String and trace the output

Core Java

Ans. private void permutation(String prefix, String sufix)
{
int ln = sufix.length();
if(ln == 0) {
System.out.println(prefix);
} else {
IntStream.range(0, ln).forEach(i->permutation(prefix sufix.charAt(i), sufix.substring(0,i) sufix.substring(i 1, ln)));
}
}

call:permutation("", "abcdef");

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Q19. Write code to create a folder if it doesn't exist.

Core Java

Ans. File folder = new File(path);

if(!folder.exists()){
try {
folder.mkdir();

} catch (Exception e) {}
}

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Q20. What is unicode ?

Core Java

Ans. A way of encoding characters as binary numbers. The Unicode character set includes
characters used in many languages, not just English. Unicode is the character set that is
used internally by Java.

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Q21. Write a program to print the index of the first non repeated character in a java string

Core Java

Ans. public class BuggyBread1{
public static void main (String args[]) {
   String str = "hheello world";
   char[] charArray = str.toCharArray();
   char selectedChar = 'a';
   for(char char1: charArray){
      if(!str.contains(Character.toString(char1).concat(Character.toString(char1)))){
         selectedChar = char1;
         break;
      }
   }
   System.out.println(str.indexOf(Character.toString(selectedChar)));
}
}

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Q22. Write a Program to add 1-100, 101-200, 201-300 in different threads and then sum the numbers ?

Core Java

Ans. public class TotalUsingThreads extends Thread{

   private static List<TotalUsingThreads> collector = new ArrayList<TotalUsingThreads>();

   private int startFrom = 0;

   private Integer threadTotal = null;

   Test(int startFrom){
      this.startFrom = startFrom;
   }


   public static void main(String[] args) throws InterruptedException{
      int totalSum = 0;

      // Create all the threads and set the count starting point for all of them
      for(int count=0;count<10;count++){
         TotalUsingThreads newThread = new TotalUsingThreads(count*100);
         newThread.start();
         collector.add(newThread);
      }

      boolean allCollected = false;


      // Make sure that all thread totals are collected and all threads have completed their tasks
      while(!allCollected){
         for(int count=0;count<10;count++){
            if(collector.get(count).threadTotal == null){
               Thread.sleep(100);
               break;
            }
         }
         allCollected = true;
      }

      // sum totals of all threads
      for(int count=0;count<10;count++){
         totalSum += collector.get(count).threadTotal;
      }

      System.out.println(totalSum);


   }

   public void run(){
      threadTotal = 0;
      for(int count=startFrom;count<startFrom+100;count++){
       threadTotal += count;
      }
   }
}

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Q23. Write a method to convert binary to a number ?

Core Java

Ans.
convert(int binaryInt) {
   int sumValue=0;
   int multiple = 1;
   while(binaryInt > 0){
      binaryDigit = binaryInt%10;
      binaryInt = binaryInt /10;
      sumValue = sumValue + (binaryDigit * multiple);
      multiple = multiple * 2;
   }
   return sumValue;
}

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Q24. What will be the output of the following code ?

String s1 = "Buggy Bread";
String s2 = "Buggy Bread";
if(s1 == s2)
System.out.println("equal 1");
String n1 = new String("Buggy Bread");
String n2 = new String("Buggy Bread");
if(n1 == n2)
System.out.println("equal 2");

Core Java

Ans. equal 1

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Q25. what will be the output of this code ?

public static void main(String[] args){
   StringBuffer s1=new StringBuffer("Buggy");
   test(s1);
   System.out.println(s1);
}

private static void test(StringBuffer s){
   s.append("Bread");
}

Core Java

Ans. BuggyBread

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Q26. what will be the output of this code ?

public static void main(String[] args)    {
   String s1=new String("Buggy");
   test(s1);
   System.out.println(s1);
}

private static void test(StringBuffer s){
   s.append("Bread");
}

Core Java

Ans. Buggy

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Q27. what will be the output of this code ?

public static void main(String[] args)    {
   StringBuffer s1=new StringBuffer("Buggy");
   test(s1);
   System.out.println(s1);
}

private static void test(StringBuffer s){
   s=new StringBuffer("Bread");
}

Core Java

Ans. Buggy

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Q28. what will be the output ?

class Animal {
public void eat() throws Exception {
}
}

class Dog2 extends Animal {
public void eat(){}
public static void main(){
Animal an = new Dog2();
an.eat();
}
}

Core Java

Ans. Compile Time Error: Unhandled exception type Exception

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Q29. What will the following code print when executed on Windows ?

public static void main(String[] args){
String parent = 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) {
e.printStackTrace();
}
}

Core Java

Ans. file.txtC:file.txtC:file.txt

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Q30. 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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