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

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Q721. Write a Program to print 1 (1 time) , 2 ( 2 times ) and so on till 100.

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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Q722. 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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Q723. 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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Q724. 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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Q725. 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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Q726. 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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Q727. 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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Q728. 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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Q729. 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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Q730. 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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Q731. 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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Q732. 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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Q733. 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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Q734. 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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Q735. 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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Q736. What are callback methods ?

Core Java

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

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Q737. What is an applet ?

Core Java

Ans. Applet is a J2EE component or a tiny application that gets executed in a widget engine ( like browser )

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Q738. What is the difference between

File f = new File("homexyz.txt");

and

File f = File.createTempFile("xyz",".txt","home"); ?

Core Java

Ans. First will not create physical file in storage whereas the second will.

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Q739. What are the benefits of creating immutable objects ?

Core Java

Ans. 1. Security and Safety - They can be shared across multiple threads as they are thread safe. Moreover, it protects then from bad state due to interception by the other code segment. One such problem due to mutability and access by alternate code segment could be the change of hash code and then the impact on its search with hash collections.

2. Reuse - In some cases they can be reused as only one copy would exist and hence it can be relied upon. For example - String Pool

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Usually asked to entry level software developers.

Q740. 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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Q741. What is memory leak ? How Java helps countering memory leaks compared to C++ ?

Core Java

Ans. Memory Leak is a situation wherein we have a reserved memory location but the program has lost its reference and hence has no way to access it.

Java doesn't have concept of Pointers, Moreover Java has concept of Garbage collection that frees up space in heap that has lost its references.

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Q742. Can we override wait() or notify() methods?

Core Java

Ans. wait and notify are declared final in object class and hence cannot be overridden.

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Q743. Can we have only try block in java ?

Core Java

Ans. No, It should be followed by either catch or finally.

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Q744. Does Java supports Default arguments ?

Core Java

Ans. No

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Q745. Explain dot(.) operator ?

Core Java

Ans. Its used to access the object properties using the object reference or class properties using the Class Name. Moreover its used to access the classes and Interfaces of a package.

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Q746. What is a class and object ?

or

How would you explain a fresher the concept of class and object in simple terms ?

Core Java

Ans. Class is a template using which objects are created in memory. It's kind of a mold using which objects with body / state are made.

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Q747. Do you feel that its useless to define hashCode method for a class ?

Core Java

Ans. Yes its useless if we are not going to use its objects within Hash collection, For example - HashSet , HashMap. HashCode is used internally by these collections for Search.

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Q748. How can be restrict creation of more than n objects in Java ?

Core Java

Ans. We can follow the same design which we follow in singleton Classes. We can have a static counter that will keep the count of number of objects already created, We can keep the constructor private and being called through the static method. We can keep incrementing the counter before calling the constructor and put a check to call only if it's lesser than n.

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Q749. What are the cursors available in Java ?

Core Java

Ans. Enumeration
Iterator
List iterator

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Q750. Which memory segment holds String Pool in Java ?

Core Java

Ans. String Pool resides in runtime constant Pool which is a part of Heap memory segment.

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