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

Interview Questions and Answers - Order By Newest

Q31. Does default methods introduce multiple inheritance and the Diamond problem in Java 8 ?

Ans. Default methods results in multiple inheritance of behavior and not of state. In case we try to implement multiple interfaces with default method having same name and signature, and don't override it in implementation class, it will throw an error.

For example -

interface MyInterface {
public void default myMethod(){
}
}

interface MyInterface2 {
public void default myMethod(){
}
}

class MyClass implements MyInterface,MyInterface2 {
}

This code will compilation error "Duplicate Default Method"

if we specify the definition of myMethod() in myClass, compiler won't complain and there is no conflict and MyClass can use overridden definition. But if we don't override myMethod() in MyClass, Java would be in conflict as to what definition should be carried to MyClass and hence throws compilation error.

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Q32. How to Change Default Boot Kernel in Linux ?

Unix

Ans. https://www.redhat.com/archives/rhl-list/2005-April/msg04167.html

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Q33. Is it mandatory to have a default constructor ?

Core Java

Ans. No.

Default constructor is provided by compiler if no constructor is provided ( argument or no argument ) by us.

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Q34. Why Java doesn't provide a default constructor if we define an argument constructor ?

Core Java

Ans. Java provides a default constructor ( no argument ) if no constructor is provided by the programmer. Java makes a check during pre compilation if there is any constructor provided by the programmer. If any constructor is provided, Java understands that programmer has provided all the mechanism for initialization and construction of the object and may not even intend to create objects by calling a no argument constructor. For example - One may like to have objects created with self defined state otherwise restrict its creation.

We make the constructor private if we want to make a class singleton as we would like to restrict creation of new objects using new operator and default constructor. Similar could be the situation wherein we would like to construct objects in a particular manner only.

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Q35. What will we get if we try to print local variable that hasn't been initialized ?

Core Java

Ans. It will print the garbage value as compiler doesn't provide a default value to local variables.

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Q36. What are the advantage of Abstract classes over interfaces with respect to Java 7 ? and What changed in Java 8 to help facilitate that in Java 8 ?

Core Java

Ans. Abstract Classes provide default implementations of methods that are inherited by the classes that extend them, which was not the case for Interfaces. This changed in Java 8, where default implementations are provided for methods.

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Q37. What could be the reason for allowing private methods in java 9 ?

Core Java

Ans. Java 8 allowed for method implementation using default methods in interfaces. As those default methods could contain complex logic and might need organizing the logic into multiple methods, they have allowed for private methods.

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Q38. Which Java version supports Interface Default methods ?

Core Java

Ans. Java 1.8 or Java 8

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Q39. What is the default size of list ? How it is growable ?

Core Java

Ans. Default size is 10.
Regard how size will increase.

Inside add() method there is one method called ensureCapacity() which will check list has enough size available.

This ensureCapacity() method if found size of list need to increase then it will call grow() method which will create new list of extra size and copy existing list data to new one and return.

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Q40. Difference between Default VPC and Custom VPC.

Amazon Web Services (AWS)

Ans. Default VPC is provided by AWS whereas custom VPC needs to be created.

All subnets in default VPC have internet access whereas it's specified by user in Custom VPC.

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Q41. What will be the output of following code ?

public class BuggyBread {

   private int x;
   private int y;

   BuggyBread(int x,int y){};

   public static void main(String[] args){
      BuggyBread buggybread = new BuggyBread();
      System.out.println(buggybread.x);
   }
}    Reference

Core Java

a. 0

b. null

c. compilation error due to uninitialized element

d. compilation error due to constructor

Ans.d. compilation error due to constructor

Q42. What will be the output of following ?

public class BuggyBread {

   private int x;
   private Integer y;

   BuggyBread(int x,int y){};

   public static void main(String[] args){
      BuggyBread buggybread = new BuggyBread(1,2);
      System.out.println(buggybread.x);
      System.out.println(buggybread.y);
   }
}    Reference

Core Java

a. 0 0

b. 0 null

c. null 0

d. null null

Ans.b. 0 null

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