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

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Q1201. Write an algorithm for square root of a given number.

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Q1202. 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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Q1203. Why packages are used in Java ?

Core Java

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Q1204. 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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Q1205. 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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Q1206. What are the different types of inheritance ?

Core Java

Ans. Single Level
Multi Level
Hierarchical
Multiple
Hybrid

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Q1207. Is there a way to access a private method from an outside class ?

Core Java

Ans. Through Reflection.

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Q1208. Difference between class and object with example.

Core Java

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Q1209. What if we use all access specifiers ? Is it encapsulation ?

Core Java

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Q1210. Explain how a class is loaded ?

Core Java

Ans. Java classLoder is resposible to load java classes.

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Q1211. How abstraction works

Core Java

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Q1212. 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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Q1213. 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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Q1214. How do you achieve String immutability ?

Core Java

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Q1215. How does hashmap works ?

Core Java

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Q1216. 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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Q1217. What are the pros and cons of Lambda expressions ?

Core Java

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Q1218. Write a code to detect the longest palindromic substring

Core Java

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Q1219. 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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Q1220. 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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Q1221. 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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Q1222. Can anonymous class implement interface and extend a class

Core Java

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Q1223. How to get collections from a Stream

Core Java

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Q1224. 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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Q1225. What is the use of toString method ?

Core Java

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Q1226. How multiple catch block works ?

Core Java

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Q1227. How does Garbage Collector work? What are the realizations of Garbage Collector.

Core Java

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Q1228. 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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Q1229. 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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Q1230. How to make a collection thread safe?

Core Java

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