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

Interview Questions and Answers - Order By Rating

Q61. How to get collections from a Stream

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Q62. Can anonymous class implement interface and extend a class

Core Java

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Q63. 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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Q64. 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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Q65. 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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Q66. Write a code to detect the longest palindromic substring

Core Java

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Q67. What are the pros and cons of Lambda expressions ?

Core Java

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Q68. 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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Q69. How does hashmap works ?

Core Java

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Q70. How do you achieve String immutability ?

Core Java

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Q71. 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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Q72. 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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Q73. How abstraction works

Core Java

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Q74. Explain how a class is loaded ?

Core Java

Ans. Java classLoder is resposible to load java classes.

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Q75. What if we use all access specifiers ? Is it encapsulation ?

Core Java

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Q76. Difference between class and object with example.

Core Java

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Q77. Is there a way to access a private method from an outside class ?

Core Java

Ans. Through Reflection.

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Q78. What are the different types of inheritance ?

Core Java

Ans. Single Level
Multi Level
Hierarchical
Multiple
Hybrid

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Q79. 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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Q80. Is it possible to have a static class ?

Core Java

Ans. We can have a static inner class but not static outer class.

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Q81. Difference between List and LinkedList ?

Core Java

Ans. A List is an child interface of collection interface in java where as Linked list is and implementation class of List interface which has doubly linked as a underlying data structure

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Q82. Why packages are used in Java ?

Core Java

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Q83. What is meant by platform ? Which platform does java provides ?

Core Java

Ans. platform is the hardware or software environment in which a program runs. There are two types of platforms software-based and hardware-based. Java provides software-based platform.

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Q84. How can we drop cookies through back end code ? Does it transfer the cookie file to the client ?

Java EE

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Q85. Is it front end code or the back end code , that drops the cookies ?

Java EE

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Q86. Write an algorithm for square root of a given number.

Core Java

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Q87. Which is faster, LinkedList or ArrayList?

Core Java

Ans. ArrayList is fast for random access, but is slow on deletion and insertion.

LinkedList is slow for random access, but is fast on deletion and insertion.

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Q88. Difference between function overloading and method overloading?

Core Java

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Q89. Which interface is used for hashset implementation ?

Core Java

Ans. HashSet implements Set interface.

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Q90. why string pool concept for only String but not for StringBuffer ?

Core Java

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