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

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Q1261. Create a custom hashmap using synchronization.

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Q1262. Explain JVM architecture.

Core Java

Ans. https://dzone.com/articles/jvm-architecture-explained

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Q1263. What is Method overloading ?

Core Java

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Q1264. What is collection framework in Java ?

Core Java

Ans. The Java collections framework (JCF) is a set of classes and interfaces that implement commonly reusable collection data structures. Although referred to as a framework, it works in a manner of a library. The JCF provides both interfaces that define various collections and classes that implement them.

Sample Code for Map

Sample Code for HashMap

Sample Code for Treemap

Sample Code for set

Sample Code for hashset

Sample Code for treeset

Sample Code for list

Sample Code for arraylist

Sample Code for linkedlist

Sample Code for queue

Sample Code for priorityqueue

Sample Code for concurrenthashmap

Sample Code for vector

Sample Code for stack

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Q1265. What is the difference between Java and J2ee ?

Java EE

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Q1266. What is Jar ?

Core Java

Ans. It is a file format based on the popular ZIP file format and is used for aggregating many files into one.

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Q1267. What is an applet ?

Java EE

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Q1268. What is the purpose of JDP and JDK ?

Core Java

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Q1269. What is an Interface ?

Core Java

Ans. The interface is a mechanism to achieve abstraction. Interfaces can have abstract methods and variables. It cannot have a method body.

Sample Code for interface

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Q1270. What is composition ?

Core Java

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Sample Code for composition

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Q1271. In the Following code which foo will get called.

foo(Integer i){
}

foo(String s){
}

public static void main(){
passing foo(null);
}

Core Java

Ans. ambiguity error

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Q1272. Can you give a real life example of synchronization

Core Java

Ans. Intersection with traffic light

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Q1273. How do you define a functional interface?

Core Java

Ans. Create interface with the only one non-overriding abstract method and annotate it with @FunctionalInterface

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Q1274. When do you use a Vector?

Core Java

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Q1275. What is Overriding ?

Core Java

Ans. Overriding refers to the Methods with same name and parameters, such that the later over rides the former method.

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Q1276. What is abstraction ?

Core Java

Ans. The process of hiding the implementation details from the user and providing only functionality.

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Q1277. Can we modify a list while iterating it ?

Core Java

Ans. No,we cannot.I t will give concurrentModificationExceptin error. It can be resolved by using ConcurrentClasses like ConcurrentHashMap,CopyOnWriteArrayList,BlockingQueue etc which are fail-safe and wont give exception.

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Q1278. What are the characteristics of the object ?

Core Java

Ans. 1. State

Instance variable or member elements forms the object state.

2. Behavior

Member functions forms the object behavior

3. Identity

Every object has a unique identity within JVM through a unique Id.

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Q1279. How can we make objects if the constructor is private ?

Core Java

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Q1280. Why String is a class in Java ?

Core Java

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Q1281. Write a Program to find number of lines , words and characters in a File.

Core Java

Ans. import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class FileUtility {

public static void main(String[] args) {
System.out.println(printFile("/home/userme/notes"));
}

private static int printFile(String filePath) {
int wordCount = 0;
try (BufferedReader br = new BufferedReader(new FileReader(filePath))) {
String line = null;
String[] wordsArray = null;

while ((line = br.readLine()) != null) {
wordsArray = line.split(" ");
wordCount = wordsArray.length;
}
} catch (IOException e) {
e.printStackTrace();
}
return wordCount;

}
}

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Q1282. Given a String with some Code, Write a Parser to have proper indentation.

Core Java

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Q1283. How do you make instance of an abstract class ?

Core Java

Ans. By extending it to the derived class and thereby creating instance of derived class.

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Q1284. Explain how Mark & Sweep is implemented in garbage collection.

Core Java

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Q1285. How would you stop a Thread in java ?

Core Java

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Q1286. Write code for serialization.

Core Java

Ans. // Java code for serialization and deserialization
// of a Java object
import java.io.*;

class Demo implements java.io.Serializable
{
   public int a;
   public String b;

   // Default constructor
   public Demo(int a, String b)
   {
      this.a = a;
      this.b = b;
   }

}

class Test
{
   public static void main(String[] args)
   {
      Demo object = new Demo(1, "geeksforgeeks");
      String filename = "file.ser";

      // Serialization
      try
      {
         //Saving of object in a file
         FileOutputStream file = new FileOutputStream(filename);
         ObjectOutputStream out = new ObjectOutputStream(file);

         // Method for serialization of object
         out.writeObject(object);

         out.close();
         file.close();

         System.out.println("Object has been serialized");

      }

      catch(IOException ex)
      {
         System.out.println("IOException is caught");
      }

      Demo object1 = null;

      // Deserialization
      try
      {
         // Reading the object from a file
         FileInputStream file = new FileInputStream(filename);
         ObjectInputStream in = new ObjectInputStream(file);

         // Method for deserialization of object
         object1 = (Demo)in.readObject();

         in.close();
         file.close();

         System.out.println("Object has been deserialized ");
         System.out.println("a = " object1.a);
         System.out.println("b = " object1.b);
      }

      catch(IOException ex)
      {
         System.out.println("IOException is caught");
      }

      catch(ClassNotFoundException ex)
      {
         System.out.println("ClassNotFoundException is caught");
      }

   }
}

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Q1287. If compareTo() method returns zero, does it mean that the objects are always equal?

Core Java

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Q1288. Write a method receiving a stream of integers, caching the last 10 min of data and returning a number if it's less than the current input

Core Java

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Q1289. How would you write a socket in Java

Core Java

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Q1290. Why do you think lambda expressions are considered such a big thing for Java 8?

Core Java

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