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

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Q361. If compareTo() method returns zero, does it mean that the objects are always equal?

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Q362. 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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Q363. How would you stop a Thread in java ?

Core Java

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Q364. Explain how Mark & Sweep is implemented in garbage collection.

Core Java

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Q365. 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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Q366. Given a String with some Code, Write a Parser to have proper indentation.

Core Java

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Q367. 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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Q368. Why String is a class in Java ?

Core Java

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Q369. Why do we need to specify import statement ? Don't you think Java could have been designed in such a way to automatically import everything that's in the class path ?

Core Java

Ans. Java could design it in such a manner but would result in ambiguity if there are multiple files with the same name. The only way to get over it to show the message when you use any such class to provide explicit import with the package prefix. The other problem could be that Java might have to change the early import to Late import and check what's being used to decide what needs to be imported as otherwise you will see errors regarding the ambiguous imports with duplicate file name.

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Q370. How can we make objects if the constructor is private ?

Core Java

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Q371. 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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Q372. 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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Q373. What is abstraction ?

Core Java

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

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Q374. 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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Q375. When do you use a Vector?

Core Java

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Q376. 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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Q377. Can you give a real life example of synchronization

Core Java

Ans. Intersection with traffic light

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Q378. 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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Q379. Find different combination of given String and trace the output

Core Java

Ans. private void permutation(String prefix, String sufix)
{
int ln = sufix.length();
if(ln == 0) {
System.out.println(prefix);
} else {
IntStream.range(0, ln).forEach(i->permutation(prefix sufix.charAt(i), sufix.substring(0,i) sufix.substring(i 1, ln)));
}
}

call:permutation("", "abcdef");

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Q380. What is composition ?

Core Java

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Sample Code for composition

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Q381. 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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Q382. What is the purpose of JDP and JDK ?

Core Java

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Q383. 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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Q384. Which collection stores element in insertion order ?

Core Java

Ans. LinkedList maintains the insertion order in collection.

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Q385. 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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Q386. What is Method overloading ?

Core Java

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Q387. Explain JVM architecture.

Core Java

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

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Q388. Create a custom hashmap using synchronization.

Core Java

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Q389. What are different methods to get the permanent gen space of running application?

Core Java

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Q390. How do you check memory leak in Java?

Core Java

Ans. You need to capture heap dump when it's in the healthy state. Start your application. Let it take real traffic for 10 minutes. At this point, capture heap dump. Heap Dump is basically the snapshot of your memory. It contains all objects that are residing in the memory, values stored in those objects, inbound

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