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

Interview Questions and Answers - Order By Newest

Q1051. Why do we use a copy constructor ?

Ans. Copy Constructor is used for creating a duplicate of another object. Duplicate object will have the same state of the copied object but will have independent values in different memory locations. Copy Constructor can be useful to create duplicates of immutable objects as the Original cannot be tampered. Moreover It can be useful if base copies are required for individual requests in threading.

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Frequently asked question in companies using Rest Web services.

Q1052. Different between POST and PUT in Rest

Rest

Ans. PUT requests are only meant to place the object as it is on server. For example - You want a file to be uploaded and then placed in a particular folder or you want an Employee object to be persisted in the table.

POST requests are also meant to transfer information from client to server but that information once received at the server is evaluated , modified or refactored before persisting.

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Q1053. Should a DB Insert Request be a POST or PUT request in Rest

Rest

Ans. It depends on whether the request object is persisted as it is

or

its first dismantled, modified or refactored and then inserted into DB.

In first case, it should be a PUT request whereas in second case it should be a POST Request.

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Q1054. Is it Necessary to send a POST request with the Payload or a body ?

Web Service

Ans. No, we can also send an empty body with the POST Request.

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Q1055. 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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Q1056. 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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Rarely asked as it was introduced with Java 8.

Q1057. 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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Q1058. 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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Q1059. 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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Q1060. 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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Q1061. 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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Q1062. 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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Q1063. 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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Q1064. 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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Q1065. Are Strings objects in Java ?

Core Java

Ans. Yes, everything except primitive types are objects in Java.

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Q1066. 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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Q1067. 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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Q1068. 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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Q1069. 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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Q1070. 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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Q1071. 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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Q1072. 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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Q1073. 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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Q1074. 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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Q1075. 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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Q1076. 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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Q1077. 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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Q1078. 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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Q1079. 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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Q1080. What are different dependency scopes in Maven ?

Maven

Ans. Compile

This is the default scope. Compile dependencies are available in all classpaths of a project. Moreover, these dependencies are propagated to dependent projects.

Provided

This is much like compile, but indicates you expect the JDK or a container to provide the dependency at runtime.

Runtime

This scope indicates that the dependency is not required for compilation, but is for execution.

Test

This scope indicates that the dependency is is only available for the test compilation and execution phases. This scope is not transitive.

System

This scope is similar to provided except that you have to provide the JAR which contains it explicitly.

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