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 Q1711. Why Collection interface does not extend Cloneable interface ?Core Java
Ans. Here is the list of classes that implements Collections Interface - http://www.buggybread.com/2015/02/java-collections-classes-that-implement.html

Having Collection interface to extend Cloneable interface would mean necessarily implement clone method by all implementing classes. As not all collection classes allow duplicate elements, it makes no sense to clone elements for them.

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   Like         Discuss         Correct / Improve     cloneable  collections  collection interface  cloning

 Q1712. How to tackle duplicate classes in maven build ?Maven
Ans. The simplest way is to ignore them if Maven enforcer plugin is complaining about it but it may lead to runtime problems later.

We can do the dependency:tree to see from where these duplicate ones are coming and hence can exclude the duplicate one.

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   Like         Discuss         Correct / Improve     maven   ban duplicate classes enforcer plugin

 Q1713. Have you heard of Ban Duplicate Classes Maven enforcer plugin ? What is its use ?Maven
Ans. Yes , we have been using this plugin with our projects and its purpose is to warn and stop the Build if there are duplicates of the same package and class are being carried either directly or through transitive dependencies. the duplicate could be coming through different types of dependencies or through different versions of the same dependency. Its purpose is to make sure that there is only one copy thats being used at compile time and runtime and hence shouldnt later result in runtime problems.

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   Like         Discuss         Correct / Improve     maven   ban duplicate classes enforcer plugin

 Q1714. What are the advantages and disadvantages of Factory Design Pattern ?Design
Ans. Object Oriented Design Patterns is the science of identifying the pattern to make objects communicate in a way to effectively implement a Solution.

Factory Design Patterns is the pattern that recommends creation of separate Factory Object for creation of other object. So its like saying - If you want to create an object of ClassA, Talk to FactoryObject ( which is an object of FactoryClass ). FactoryObject in itself encapsulates the inputs and logic required to make the decision regarding the creation and construction of object.

Advantage of Factory Pattern - Loose Coupling and Segregation of Responsibilities. Now instead of hard binding the complete logic to decide the nature and shape of the object on the basis of some conditions, you are assigning the responsibility to some other object and hence making the relationship loosely coupled and hence main tenable.

Disadvantages - Before Understanding the Dis-advantages , we should understand that these patterns were chosen after a period of evolution and research and almost best fit for the required solution, otherwise these patterns would have easily been replaced by now.

Though the advantages of these pattern surpass the disadvantages keeping in mind the decreasing cost of resources and increasing scale of applications, but still loose coupling by means of additional objects results in decreased performance.

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   Like         Discuss         Correct / Improve     factory design pattern  design pattern

 Q1715. What are the benefits of Enums ?Core Java
Ans. Enums in Java are used to declare predefined objects and then reuse them. they offer many benefits

1. Enum instance are type safe and thread safe.

2. Enum instances are singleton and hence reused.

3. If we use Enums with Switch , It makes sure that the passed argument is either of its instance and hence provides a safeguard.

4. If we use Enum with Sorted Collections we can sort the elements with a predefined priorities ( as per constant declaration in enum )

5. We can use Enum as a Factory by defining its constructor.

6. We can store related constant data within enum. For example - If we know the values for the map upfront, we can alternatively use an enum.

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   Like         Discuss         Correct / Improve          Asked in 6 Companies

 Q1716. What is System.in in Java ?Core Java
Ans. It is an InputSream which is usually connected to the keyboard input of console program.

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   Like         Discuss         Correct / Improve     System.in  Input Stream  Input Output

 Q1717. How is == operator different for objects and primitive types ? Core Java
Ans. For objects or references, == operator check if the reference on left and right points to the same object.

For primitive types or variables, == operator check if the variable on left and right holds the same value.

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   Like         Discuss         Correct / Improve     ==  object equality  operator      Basic

 Q1718. What is the difference between = and == in Java ?Core Java
Ans. = is the assignment operator that assigns the result of the expression on the right to the variable on the left, whereas

== is the operator to check object equality to see if the reference on left and right are pointing to the same object. For primitive types, its used to check if both variables holds the same value.

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   Like         Discuss         Correct / Improve     =  ==  assignment operator  object equality  difference between      Basic

 Q1719. Write a class explaining builder pattern ?Design
Ans. 
public class BuggyBread { 



   private String element1; 



   private String element2; 



   private BuggyBread(String element1, String element2){ 

      this.element1 = element1; 

      this.element2 = element2; 

   } 



   public static class Builder { 

    

      private String element1; 



      private String element2; 



      Builder(BuggyBread buggybread){ 

         element1 = buggybread.element1; 

         element2 = buggybread.element2; 

      } 



      Builder withElement1(String element1){ 

         this.element1 = element1; 

         return this; 

      } 



      Builder withElement2(String element2){ 

         this.element2 = element2; 

         return this; 

      } 



      BuggyBread build(){ 

         BuggyBread buggybread = new BuggyBread(element1,element2); 

         return buggybread; 

      } 

   } 

}


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 Q1720. What is a classpath in Java ?Core Java
Ans. Classpath is the parameter for JVM to look for java classes ( .class files ) that are to be looad by class loader

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   Like         Discuss         Correct / Improve     classpath     Asked in 1 Companies      basic

 Q1721. What is meant by size and index of a collection ?Core Java
Ans. As the name suggest size is the size of collection / data structure i.e number of elements or memory utilized by the collection.

Index is the position of an element in a collection or data structure.

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   Like         Discuss         Correct / Improve     collection  index of collection  size of collection      Basic

 Q1722. Difference between multiple and multi level inheritance ?Core Java
Ans. Multiple Inheritance refers to the concept of a class inheriting multiple classes. Example - Class C extends Class A ,Class B. This is not allowed in Java.

Multilevel Inheritance refers to the concept of Inheritance in a chain. Example - Class B extends Class A, Class C extends Class B. This is permitted in Java.

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   Like         Discuss         Correct / Improve     inheritance  object oriented programming (oops)  oops concepts   multiple inheritance  object oriented programming (oops)  oops concepts   multi level inheritance  object oriented programming (oops)  oops concepts      Basic        frequent

 Q1723. Where do we generally use comparable interface ?Core Java
Ans. Implementing Comparable interface means that the elements of the class are comparable i.e the class provides the implementation of compareTo method that would help comparing the elements.

This is usually required if we are planning to sort elements of a collection, If compareTo method is not defined , the sorting class / method could never understand a way to compare its elements in order to sort them.

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   Like         Discuss         Correct / Improve     comparable interface
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 Q1724. How and when the Buffer is cleared when using Buffered Writer Classes ?Core Java
Ans. Buffer is cleared in 2 circumstances, i.e 1. naturally when the buffer is filled and 2. explicitly when the method flush is called ( for flushing the residual )

Ideally we just need to call flush once at the end of file writing so that the residual content should be dumped to file.

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   Like         Discuss         Correct / Improve     BufferedWriter  Writer  PrintWriter  File io  flush  file handling

 Q1725. What is IdentityHashMap ?Core Java
Ans. IdentityHashMap is a class that implements AbstractMap and provides a data structure with Elements having Key Value pair, just like HashMap. It is similar to HashMap except that it uses reference equality when comparing elements.

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   Like         Discuss         Correct / Improve     IdentityHashMap  map  hashmap  collections

 Q1726. Do we need to implement all interface methods if a class is implementing it ?Core Java
Ans. Yes, a Class is supposed to define all abstract methods declared in the interface. With Java 8 , Interfaces can have default methods which need not be implemented by the implementing class.

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 Q1727. Can we access private members of the parent class ? i.e Are private members of the class visible in the derived class ?Core Java
Ans. No, If both Parent and Derived are outer classes.

public class Vehicle {
private static String manufacturingDate = "2016";
}

public class Car extends Vehicle{
public static void main(String args[]){
System.out.println(manufacturingDate); // error - The field Vehicle.manufacturingDate is not visible
}
}

Yes, If derived is the inner class of Parent.

public class Vehicle {
private static String manufacturingDate = "2016";
static public class Car extends Vehicle{
public static void main(String args[]){
System.out.println(manufacturingDate); // no problem
}
}
}

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   Like         Discuss         Correct / Improve     private members   private methods   private variables   inheritance  object oriented programming (oops)  oops concepts   members visibility   inner classes  nexted classes      basic        frequent

 Q1728. Are Strings objects in Java ?Core Java
Ans. Yes, everything except primitive types are objects in Java.

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   Like         Discuss         Correct / Improve     string

 Q1729. Does an ArrayList allow elements of different types ? If not, Why the following code works List list1 = new ArrayList<>(); list1.add(1); list1.add("1");Core Java
Ans. With Java 7 or Later. If you don't declare the list to be of specific type , it treats it as list of objects. int 1 is auto boxed to Integer and "1" is String and hence both are objects.

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   Like         Discuss         Correct / Improve     arraylist  list  collections

 Q1730. Does it make sense to clone an object which is supposed to be immutable ?Design
Ans. It make sense only if we intend to modify either of the object and would like to preserve original state in other. Otherwise we can reuse the original object by making it singleton.

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   Like         Discuss         Correct / Improve     clone  clone objects  prototype design pattern   immutable  immutability  immutability  cloning

 Q1731. What are design situations to use Singleton and Prototype Design Pattern ?Design
Ans. Both are creational design patterns.

Singleton is used when we would like to reuse an object if object is not supposed to hold request or thread specific information. Inversely Prototype is used in situations where we would like to reuse the object information but the request / thread may require it own data to be persisted.

In short, Singleton is used in situations where we can live with single object being shared across multiple requests or threads whereas Prototype is used when we need duplicate copies of objects.

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   Like         Discuss         Correct / Improve     design pattern  singleton  prototype  creational design pattrn     Asked in 7 Companies      expert
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 Q1732. What is wrong with the following if statement ?

if(x==y || x.equals(y) {
}		Core Java
Ans. if x==y turns out to be true x.equals(y) will be true too. If x.equals(y) could be true even if x==y is true or not.

So the only possible outcomes are

1 || 1 = 1
0 || 1 = 1
0 || 0 = 0

i.e the outcome of x.equals(y)

check for x==y is not required in this if statement.

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   Like         Discuss         Correct / Improve     if statement  control statements  == and equals  ==  .equals   code optimization
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 Q1733. What is wrong with the following if statement ?

if(x==y && x.equals(y) {
}		Core Java
Ans. x==y means that both references have same type and are pointing to same memory location and hence would always mean that they have same value.

x.equals(y) is not required in this case.

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   Like         Discuss         Correct / Improve     if statement  control statements  == and equals  ==  .equals   code optimization
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 Q1734. Difference between Hot and Cold Deployment ?Server
Ans. Cold Deployment is a conventional deployment mechanism that follows the multi step process to deploy code changes to the running app i.e Build -> Deploy - Restart.

whereas

Hot Deployment is deployment changes on the fly without need to first build , deploy and then restart. All these functions happens on the fly as soon as the changes are made to the code.

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   Like         Discuss         Correct / Improve     Hot deployment  cold deployment  application server  production support

 Q1735. What is Hot Deployment ?Server
Ans. It is the ability to deploy changes on the fly without need to first build , deploy and then restart. All these functions happens on the fly as soon as the changes are made to the code.

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   Like         Discuss         Correct / Improve     hot deployment  deployment   container   application server  production support

 Q1736. Can we declare the main method as private ?Core Java
Ans. Yes, compiler won't complain but at runtime it will give an error saying "Error: Main method not found in class". Even though we can use this method as any other private method, it cannot be invocate by executing the class.

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   Like         Discuss         Correct / Improve     main method   main method visibility      basic
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Rarely asked as it was introduced with Java 8.
 Q1737. What is the use of :: operator wef from Java 8 ?Core Java
Ans. We can refer to a function using this operator like System.out.println(intList.stream().reduce(Math::max).get());

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   Like         Discuss         Correct / Improve     :: operator   lambda expression  java 8

  Q1738. Difference between GET and POST Requests ?Web Service
Ans. GET is supposed to get information from the server. Client sends the minimal information so that Server can respond with the response body on basis of request. For example - You want to get complete employment record for employee id 123

POST is supposed to send the information for submission. Payload or a Body is usually sent so that it can be persisted on the server. For example - Sending the complete information of an employee ( id, name , dept etc ) to the server for persisting it.

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   Like         Discuss         Correct / Improve     get vs post   web service   rest     Asked in 11 Companies      basic        frequent

 Q1739. What are the different ways in which information can be sent to server in web service call ?Web Service
Ans. 1. As Request Param
2. As Path Param
3. Part of Payload / Body in case of PUT and POST Request

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   Like         Discuss         Correct / Improve     web service   rest      basic        frequent

 Q1740. Can I hit the Rest Post Request through a browser address bar if it's not expecting any payload / body ? Rest
Ans. No, even if there is no payload, you can't hit the POST request by typing it into browser address bar. You will need a client that can make a POST Request.

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   Like         Discuss         Correct / Improve     Post Request   Rest  Calling Rest service through browser        rare

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