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

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Q601. What are callback methods ?

Core Java

Ans. Component methods called by the container to notify the component of the events

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Q602. How and Why Strings are interned in Java ?

Core Java

Ans. String class has a public method intern() that returns a canonical representation for the string object. String class privately maintains a pool of strings, where String literals are automatically interned.

these are automatically interned so as to have efficient String comparison using == operator instead of equals which is usually slower.

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Q603. What will be the output of following code ?

Base Interface

public interface BaseInterface {
   int i = 4;
}

Derived Interfaces

public interface DerivedInterface1 extends BaseInterface{
   int i = 5;
}

public interface DerivedInterface2 extends BaseInterface{
   int i=6;
}

Implementing Class

public class Class implements DerivedInterface1,DerivedInterface2 {
   public static void main(String[] args){
      System.out.println(BaseInterface.i);
   }
}

What will be the output upon executing main and Why ?

Core Java

Ans. It will print 4 because member elements of an interface are implicitly static and hence the concept of overriding doesn't work.

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Q604. What will be the output of following code ?

Base Interface

public interface BaseInterface {
   int i = 4;
}

Derived Interfaces

public interface DerivedInterface1 extends BaseInterface{
   int i = 5;
}

public interface DerivedInterface2 extends BaseInterface{
   int i=6;
}

Implementing Class

public class Class implements DerivedInterface1,DerivedInterface2 {
int i=10;

public static void main(String[] args){
      System.out.println(new Class().i);
   }
}

What will be the output upon executing main and Why ?

Core Java

Ans. 10

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Q605. What is the difference between compilation and decompilation ?

Core Java

Ans. Compilation is the process of converting Java source files to class files which can be executed by the Java runtime environment whereas Decompilation is the process of converting class files back to the Java Source code.

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Q606. Write a class / program that takes few numbers from the input and then output the average ?

Core Java

Ans. public class Class{
   public static void main(String[] args){
      List<Integer> collector = new ArrayList();

      Scanner scanner = new Scanner(System.in);
      int x = scanner.nextInt();
      while(x != 0){
         collector.add(x);
         x = scanner.nextInt();
      }
      System.out.println(collector.stream().collect(Collectors.averagingInt(p->((Integer)p))));
   }
}

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Q607. Write a program to check is a string is substring of another ?

Core Java

Ans. public class Class{
   public static void main(String[] args){
      String string1 = "Hello I am Jack. I live in United States. I live in california state.";

      String string2 = "I live in";

      if(string1.indexOf(string2) >= -1){
         System.out.println("string2 is sub string of string1");
      } else {
         System.out.println("string2 is not sub string of string1");
      }
   }
}

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Q608. Write a Program to check number of occurrences of one string within another ?

Core Java

Ans. public class Class{
   public static void main(String[] args){
      String string1 = "Hello I am Jack. I live in United States. I live in california state.";

      String string2 = "I live in";

      int startIndex = 0;
      int endIndex = string1.length()-1;

      int countNoOfOccurences = 0;

      String remainingString = string1;

      while(startIndex < endIndex){
         if(remainingString.indexOf(string2) != -1){
            countNoOfOccurences++;
            startIndex = remainingString.indexOf(string2) + string2.length();
            remainingString = remainingString.substring(startIndex);
         } else {
            break;
         }
      }

      System.out.println(countNoOfOccurences);
   }
}

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Q609. Write a Program to check if string is a Colidrome ?
(Colidrome is a word that has n alphabets followed by the reverse of the n alphabets, for ex - mallom)

Core Java

Ans.
public class Class {
   public static void main(String[] args) {
      String str = "mallam";
      String firstHalf = str.substring(0, str.length() / 2);
      String secondHalf = str.substring(str.length() / 2);

      if (firstHalf.equals(new StringBuilder(secondHalf).reverse().toString())) {
         System.out.println("It's a Colidrome");
      } else {
         System.out.println("It's not a Colidrome");
      }
   }
}

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Q610. Write a program in Java that prints the numbers from 1 to 100. But for multiples of three print Fizz instead of the number and for the multiples of five print Buz. For numbers which are multiples of both three and five print FizzBuzz

Core Java

Ans. public class Class{
public static void main(String[] args){
for(int i=1;i<= 100;i++){
if(i%3 == 0){
if(i%5 == 0){
System.out.println("FizzBuzz");
}
System.out.println("Fizz");
} else if(i%5 == 0){
System.out.println("Buzz");
} else {
System.out.println(i);
}

}
}
}

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Q611. Write a Program to print count of each character in a String.

Core Java

Ans. public class BuggyBread {
public static void main(String args[]) {
Map<Character, Integer> countMap = new HashMap();
String str = "hello world";
for (char character : str.toCharArray()) {
if (countMap.containsKey(character)) {
countMap.put(character, countMap.get(character) + 1);
} else {
countMap.put(character, 1);
}
}
System.out.println(countMap);
}
}

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Q612. Write a Program to only print characters that have occured more than once in a String

Core Java

Ans. public class BuggyBread{
public static void main (String args[]) {
Set<Character> set = new HashSet();
Set<Character> setWithDuplicateChar = new HashSet();
String str = "hello world";
for(char character: str.toCharArray()){
if(set.contains(character)){
setWithDuplicateChar.add(character);
} else {
set.add(character);
}
}

System.out.println(setWithDuplicateChar);
}
}

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Q613. Write a Program to print all numbers till 100 that are divisible by 5

Core Java

Ans. public class BuggyBread{
public static void main (String args[]) {
   for(int counter=1;counter<=100;counter++){
      if(counter % 5 == 0){
         System.out.println(counter);
      }
   }
}
}

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Q614. Write a Program to print 1 (1 time) , 2 ( 2 times ) and so on till 100.

Core Java

Ans. public class BuggyBread1{
public static void main (String args[]) {
   for(int x=1;x<=100;x++){
      for(int y=1;y <= x;y++){
         System.out.println(x);
      }
   }
}
}

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Q615. Write a Program to print series like

1
12
123
1234
12345

till 100

Core Java

Ans. public class BuggyBread{
public static void main (String args[]) {
   for(int x=1;x<=100;x++){
      for(int y=1;y <= x;y++){
         System.out.print(y);
      }
      System.out.println("
");
   }
}
}

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Q616. Write a program for 0 and cross games?

Core Java

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

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Q617. Given a sorted array, write a program to check if two elements sum up to third.

Core Java

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

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Q618. Write a program to print two digit numbers that fulfil following criteria

Summing their digits and then multiplying with 3 should result in the number

For ex - 27 , (2+7) * 3 = 27

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
      for(int x=10;x<100;x++){
         int tensDigit = x/10;
         int unitDigit = x%10;

         if((tensDigit+unitDigit)*3 == x){
            System.out.println(x);
         }
      }
   }
}

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Q619. Write Code showing Inheritance

Core Java

Ans. class A {
public void test() {
System.out.println("Class A Test");
}
}

class B extends A {
public void test() {
System.out.println("Class B Test");
}
}

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Q620. Write a Program / Code showing Inheritance and overridding

Core Java

Ans. class A {
public void test() {
System.out.println("Class A Test");
}
}

class B extends A {
public void test() {
System.out.println("Class B Test");
}

public static void main(String[] args){
A a = new B();
a.test(); // will print Class B Test
}
}

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Q621. Write a Program to find the longest word in a string

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
      String str = "We are what we repeatedly do; excellence, then, is not an act but a habit.";
      String longestWord = "";

      str = str.replaceAll(",","");
      str = str.replaceAll(";","");
      str = str.replaceAll("/.","");

      for(String word: str.split(" ")){
         if(word.length() > longestWord.length()){
            longestWord = word;
         }
      }

      System.out.println(longestWord);
   }
}

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Q622. Write a Program that prints the repeated words in a String

For example -

We are what we repeatedly do; excellence, then, is not an act but a habit.

should print we, should count for case insensitive words too

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
      Map<String,Integer> wordLength = new HashMap();

      String str = "We are what we repeatedly do; excellence, then, is not an act but a habit.";
      String longestWord = "";

      str = str.replaceAll(",","");
      str = str.replaceAll(";","");
      str = str.replaceAll("/.","");
      str = str.toLowerCase();

      for(String word: str.split(" ")){
         if(wordLength.containsKey(word)){
            wordLength.put(word, wordLength.get(word).intValue() + 1);
         } else {
            wordLength.put(word, 1);
         }
      }

      for(Map.Entry<String, Integer> entry:wordLength.entrySet()){
         if(entry.getValue().intValue() > 1){
            System.out.println(entry.getKey());
         }
      }
   }
}

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Q623. Write a Program that prints words longer than 5 characters in a String

For example

We are what we repeatedly do; excellence, then, is not an act but a habit

should print

repeatedly
excellence

Core Java

Ans. public class BuggyBread1 {
   public static void main(String args[]) {
      Map<String,Integer> wordLength = new HashMap();

      String str = "We are what we repeatedly do; excellence, then, is not an act but a habit";
      String longestWord = "";

      str = str.replaceAll(",","");
      str = str.replaceAll(";","");
      str = str.toLowerCase();

      for(String word: str.split(" ")){
            wordLength.put(word, word.length());
      }

      for(Map.Entry<String, Integer> entry:wordLength.entrySet()){
         if(entry.getValue().intValue() > 5){
            System.out.println(entry.getKey());
         }
      }
   }
}

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Q624. Write a Program to print 3 smallest words in a String

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
      Map<String,Integer> wordLength = new HashMap();

      String str = "We are what we repeatedly do; excellence, then, is not an act but a habit";

      str = str.replaceAll(",","");
      str = str.replaceAll(";","");
      str = str.toLowerCase();

      for(String word: str.split(" ")){
            wordLength.put(word, word.length());
      }

      List<Map.Entry<String, Integer>> list = new LinkedList<Map.Entry<String, Integer>>( wordLength.entrySet() );

      Collections.sort( list, new Comparator<Map.Entry<String, Integer>>()
{
public int compare( Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2 )
{
return (o1.getValue()).compareTo( o2.getValue() );
}
} );

      int countWords = 1;

      for(Map.Entry<String, Integer> entry:list){
         if(countWords <= 3){
            System.out.println(entry.getKey());
         }

         countWords++;

      }
   }
}

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Q625. Write a Program to print 3 largest words in a String

Core Java

Ans. public class BuggyBread {
public static void main(String args[]) {
Map<String,Integer> wordLength = new HashMap();

String str = "We are what we repeatedly do; excellence, then, is not an act but a habit";

str = str.replaceAll(",","");
str = str.replaceAll(";","");
str = str.toLowerCase();

for(String word: str.split(" ")){
wordLength.put(word, word.length());
}

List<Map.Entry<String, Integer>> list = new LinkedList<Map.Entry<String, Integer>>( wordLength.entrySet() );

Collections.sort( list, new Comparator<Map.Entry<String, Integer>>()
{
public int compare( Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2 )
{
return (o1.getValue()).compareTo( o2.getValue() ) * -1;
}
} );

int countWords = 1;

for(Map.Entry<String, Integer> entry:list){
if(countWords <= 3){
System.out.println(entry.getKey());
}

countWords++;

}
}
}

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Q626. Write a Program to Sort entries of a map by its value

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
      Map<String,Integer> wordLength = new HashMap();

      String str = "We are what we repeatedly do; excellence, then, is not an act but a habit";

      for(String word: str.split(" ")){
            wordLength.put(word, word.length());
      }

      List<Map.Entry<String, Integer>> list = new LinkedList<Map.Entry<String, Integer>>( wordLength.entrySet() );

      Collections.sort( list, new Comparator<Map.Entry<String, Integer>>()
{
public int compare( Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2 )
{
return (o1.getValue()).compareTo( o2.getValue() ) * -1;
}
} );

      System.out.println(list);

   }
}

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Q627. Write a Program to remove all spaces in a String

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {

      String str = "We are what we repeatedly do; excellence, then, is not an act but a habit";

      System.out.println(str.replaceAll(" ", ""));
   }
}

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Q628. Write a Program to remove multiple spaces

For example

We are what we repeatedly do; excellence, then, is not an act but a habit

should result in

We are what we repeatedly do; excellence, then, is not an act but a habit

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
      String str = "We are what we repeatedly do; excellence, then, is not an act but a habit";

      String[] splittedString = str.split(" ");

      for(String word: splittedString){
         word = word.trim();
         if(!word.equals("")){
            System.out.print(word.trim());
            System.out.print(" ");
         }
      }


   }
}

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Q629. What are the ways to Reuse Code in Java ?

Core Java

Ans. 1. Object Level Reuse - private methods
2. Class Level Reuse - static methods
3. package level Reuse - default methods
4. Application Level Reuse - Classes
5. Multiple Applications Level Reuse - Libraries , Frameworks

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Q630. What are the different primitive data types in Java ?

Core Java

Ans. boolean
byte
char
double
float
int
long
short
void

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