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

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Q31. Can we assign the reference to this variable ?

Core Java

Ans. No

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Q32. Hash map using/without using Java 8

Core Java

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Q33. What is Throwable ?

Core Java

Ans. Throwable in java is a class that is the superclass of all exceptions and errors which may occurs in java program.It extends obcect class.

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Q34. What is string pool and what is the use of intern() function ?

Core Java

Ans. The Java String class intern() method returns the interned string. It returns the canonical representation of string.

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Q35. How to make a collection thread safe?

Core Java

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Q36. What is a comparator ?

Core Java

Ans. Java Comparator compares two Java objects in a “compare(Object 01, Object 02)” format. Using configurable methods, Java Comparator can compare objects to return an integer based on a positive, equal or negative comparison

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Q37. Why should we go for custom defined exceptions even if we have many exceptions provided already using throw keyword

Core Java

Ans. It gives us the liberty to throw the specific exceptions which are required and also we can control the handling of exceptions

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Q38. How does Garbage Collector work? What are the realizations of Garbage Collector.

Core Java

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Q39. How multiple catch block works ?

Core Java

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Q40. What is the use of toString method ?

Core Java

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Q41. Class and Object methods.

Core Java

Ans. class:- A class describe the contents of an object, an it describe the detail of data field called instance variable and defines the operations called method.

Object:-An object is an element of a class. Object have the behaviors of their class.

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Q42. How to get collections from a Stream

Core Java

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Q43. Can anonymous class implement interface and extend a class

Core Java

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Q44. What is ServerSocket in Java ?

Core Java

Ans. This class implements server sockets. A server socket waits for requests to come in over the network. It performs some operation based on that request, and then possibly returns a result to the requester.

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Q45. What are the distinguished qualities in Java that no other language possess ?

Core Java

Ans. Java is widely adopted as an enterprise standard technology across business domains and technical domains ( Web , Desktop , mobile , data science etc ) and has a vast ecosystem of frameworks and libraries.

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Q46. What is headless mode in Java ? Why is it used ?

Core Java

Ans. It’s a mode that can be used for creating Back end application without the front end UI.

The advantage is that it reduces the number of packages that needs to be loaded ( by ignoring ui packages )

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Q47. Write a code to detect the longest palindromic substring

Core Java

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Q48. What are the pros and cons of Lambda expressions ?

Core Java

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Q49. Write a program to rotate a matrix.

Core Java

Ans. public class Matrix {

   public static void main(String[] args) {
      int[][] matrix = {
            {1, 2, 3},
            {4, 5, 6},
            {7, 8, 9}
      };
      Matrix.rotateMatrix(matrix);
      for (int i = 0; i < matrix.length; i ){
         for (int j = 0; j < matrix.length; j ){
            System.out.print(matrix[i][j] " ");
         }
         System.out.println();
      }
   }

   public static void rotateMatrix(int[][] matrix){
      int row = matrix.length;
      //first find the transpose of the matrix.
      for (int i = 0; i < row; i ){
         for (int j = i; j < row; j ){
            int temp = matrix[i][j];
            matrix[i][j] = matrix[j][i];
            matrix[j][i] = temp;
         }
      }
      //reverse each row
      for (int i = 0; i< row; i ){
         for(int j = 0; j< row/2; j ){
            int temp = matrix[i][j];
            matrix[i][j] = matrix[i][row - 1 - j];
            matrix[i][row - 1 - j] = temp;
         }
      }

   }

}

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Q50. How does hashmap works ?

Core Java

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Q51. How do you achieve String immutability ?

Core Java

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Q52. Can we override behavior of a collection class ? How ?

Core Java

Ans. Yes. We can do that.

1. We can create own own implementation class extending the collection class and then override the behavior method.

2. We can override the behavior at the time of instantiation of class as following

List<MyType> list = new ArrayList<MyType>() {
public boolean add(MyType mt) {
super.add(mt);
Collections.sort(list, comparator);
return true;
}
};

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Q53. What is the difference between map and filter methods in streams ?

Core Java

Ans. By using map , you can transform the object values. The map operation allows us to apply a function, that takes input parameter of one type, and returns something else.

Filter is used for filtering the data, it always returns the boolean value. If it returns true, then item is added to list else its filtered out (ignored)

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Q54. How abstraction works

Core Java

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Q55. Explain how a class is loaded ?

Core Java

Ans. Java classLoder is resposible to load java classes.

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Q56. What if we use all access specifiers ? Is it encapsulation ?

Core Java

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Q57. Difference between class and object with example.

Core Java

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Q58. Is there a way to access a private method from an outside class ?

Core Java

Ans. Through Reflection.

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Q59. What are the different types of inheritance ?

Core Java

Ans. Single Level
Multi Level
Hierarchical
Multiple
Hybrid

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Q60. Why in Java does it require "static" in the main function?

Core Java

Ans. Because there needs to be a starting point till when there is no object created in memory and hence it needs to be run in static scope

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