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Interview Questions and Answers - Order By Newest

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 Q61. What is the use of MethodHandle ?
Ans. MethodHandle is a modern, more flexible, more typesafe way of doing reflection.

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   Like         Discuss         Correct / Improve     MethodHandle  Reflection

 Q62. What are instance methods ?
Ans. All methods defined in a class that are not marked static are actually instance methods.

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   Like         Discuss         Correct / Improve     methods  functions

 Q63. Is a method name same as Class name permissible in Java ?
Ans. Yes, But the method should have some return type as otherwise it will be treated as a constructor.

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   Like         Discuss         Correct / Improve     constructor  methods  method names
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 Q64. Can we declare a main method as abstract ?
Ans. No. Static methods cannot be overridden and hence make no sense to be declared abstract.

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   Like         Discuss         Correct / Improve     main method   abstract
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 Q65. Can we send a request body with the Get Request ? If not, What is the alternate to pass message to the Get Request ?Web Service
Ans. Request Body in case of Get Request has no meaning and hence it's not parsed when the request is received. Alternatively Request Parameters are passed as either Path Params or Query Params.

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   Like         Discuss         Correct / Improve     rest  web services  http  http methods  get request

 Q66. Do all java classes need a main method?
Ans. No, Main method is the entry point into an application. An application usually contain multiple classes to perform a function.

Lets take an example of a House, House usually have only one external Door and you may have internal doors to move around within a house. Internal Doors are methods of classes whereas External Door is a special method called main method.

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   Like         Discuss         Correct / Improve     main method

 Q67. Does default methods introduce multiple inheritance and the Diamond problem in Java 8 ?Core Java
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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   Like         Discuss         Correct / Improve     default methods  java 8  multiple inheritance  object oriented programming (oops)  oops concepts  diamond problem   interfaces

 Q68. 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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 Q69. 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

 Q70. What could be the problems due to the usage of static methods and elements ? Core Java
Ans. static methods and static elements are shared by all objects of a class and hence could create problem.

Static methods are not synchronized by default and hence could create problem when accessed through multiple threads. Static elements are shareable by class and hence state of one object could be altered by another object.

Some limitations with Unit testing as not all mocking framework facilitate mocking them. Power mock allows but Mockito doesn't

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   Like         Discuss         Correct / Improve     static  static method  static variables

 Q71. Why main method is declared static ?Core Java
Ans. static is the keyword that makes it accessible even without creating any object and using class name only. Making it non static would like creation of object upfront before calling the method.

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   Like         Discuss         Correct / Improve     main method  static     Asked in 4 Companies      Basic

 Q72. Can an application have multiple main methods within different classes ? If yes, How will the app decide which one to be executed ?Core Java
Ans. Yes we can have a main method with string[] argument in every class of an application. When we execute an app we specify the starting point i.e the class that will get the control first and hence main method of that class gets executed.

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   Like         Discuss         Correct / Improve     main method     Asked in 3 Companies

 Q73. Who invokes a thread's run method ?Core Java
Ans. After a thread is started using a call to start method, JVM invokes the thread’s run method when the thread is initially executed.

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   Like         Discuss         Correct / Improve     threads  thread run method     Asked in 1 Companies

 Q74. What is a method reference in Java ?Core Java
Ans. Introduced with java 8 , Method References help us to point to methods by their name.

A method references is described using :: symbol

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   Like         Discuss         Correct / Improve     method reference  java 8  lambda expressions

 Q75. Can we override abstract methods ?Core Java
Ans. Abstract methods are the methods that need to be overridden in the derived class ( either as implementing method or again abstract method ) so it's not only allowed but its required to override abstract method in the derived class.

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   Like         Discuss         Correct / Improve     overriding  abstract methods  overriding abstract methods

 Q76. Can we override an abstract method with abstract method in the derived class ?Core Java
Ans. Yes, but in that case the derived class itself should be abstract. We cannot have an object of a class without definition for the method which has been declared abstract in the parent.

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   Like         Discuss         Correct / Improve     overriding  overriding abstract methods  abstract methods

 Q77. What is a mutator in Java?Core Java
Ans. Mutator is another name for setter methods, i.e the method allows for mutating the property of an object and eventually the state of the object.

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   Like         Discuss         Correct / Improve     setter method  mutator

 Q78. Is it a good practice to override static methods ?Design
Ans. Though it's useful but it's not as useful as overriding member or object methods. We cannot achieve polymorphic behavior with static methods by overriding their definition in derived class.

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   Like         Discuss         Correct / Improve     override static methods

 Q79. If we don't provide any argument to the executed program, What arguments will be passed to the main method ? Will the String array argument be null ?Core Java
Ans. No. It won't be null but an empty array with size 0

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   Like         Discuss         Correct / Improve     main method

 Q80. In Java, if object A contains same the same data of object B, are they equal?Core Java
Ans. it depends on the implementation of equals method of the respective class. If no definition is provided and it uses the default definition of the object class, two references are equal only if they point to the same object.

We can have such an equality defined for a particular class objects if we provide appropriate implementation of equals method comparing all those fields.

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   Like         Discuss         Correct / Improve     equals  equals method

 Q81. What are the trade offs between public constructor and static final method ?Core Java
Ans. Public constructor is simple and easy as it's the default way of object creation. So there are no additional coding overheads as compiler provides the default constructor if none is provided by coder.

With static final methods, it facilitates loose coupling by segregating the responsibility of object creation to a separate method. Validation can be done on the constructor arguments before calling it. Moreover if any adaption on the arguments is required that can achieved easily with factory method.On the flip side, there is coding overhead and additional method call.

  Sample Code for constructor

  Sample Code for factory

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   Like         Discuss         Correct / Improve     constructor  factory design pattern  factory method

 Q82. What are the advantages and disadvantages of using lock classes from java.util.concurrent.locks vs. synchronized methods ?Core Java
Ans. http://www.devinline.com/2015/10/Lock-Vs-synchronized-in-java.html

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   Like         Discuss         Correct / Improve     java.util.concurrent.locks  synchronization  synchronized methods

 Q83. Does all methods need to have a return type ? Is it applicable to constructors too ?Core Java
Ans. All methods are not expected to return something but Yes, all methods are expected to have a return type. If a method returns nothing, it can be declared with the return type void.

Constructors are not expected to have any return types , not even void.

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   Like         Discuss         Correct / Improve     return type   method  constructor

 Q84. What is the difference between the 2 methods in Java ?

Class BuggyBread {

BuggyBread(){
}
void BuggyBread(){
}
}		Core Java
Ans. BuggyBread method without any return type is the constructor which get's called upon object creation whereas BuggyBread method with return type of void is just another method that needs to be called explicitly for it's invocation.

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   Like         Discuss         Correct / Improve     method  return type  constructor

 Q85. What are var args ?

or

What is the use of var args ?		Core Java
Ans. Var args is the feature of Java that allows a method to have variable number of arguments. Var args are used when we are not sure about the number of arguments a method may need. Internally java treats them as array.

Declarations of methods with var args

void method(int... x){};
void method(int x, int... y){};

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   Like         Discuss         Correct / Improve     var args  methods  functions   method declaration     Asked in 2 Companies

 Q86. Why following method declarations are not valid ?

void method(int... x, int y){};
void method(int... x,int... y){};		Core Java
Ans. Because var args are not only allowed with the last argument in the method declaration.

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   Like         Discuss         Correct / Improve     var args  methods  functions   method declaration  ocjp  scjp

 Q87. Which method will get called if we call it as method(1)

void method(int x ){};
void method(int... x){};		Core Java
Ans. Though the call an be bind to either of these but in this case, 1st method will get priority and hence will be called.

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   Like         Discuss         Correct / Improve     var args  method  function  overloading  scjp  ocjp

 Q88. Do you see any problem with this code

public class BuggyBread {

   public static void main(String[] args) {
      method("Hello","World");
   }

   private static void method(String... args){
      for(String arg:args){
         System.out.println(arg);
      }
   }
}		Core Java
Ans. No, It will compile and execute perfectly fine. As we are using method with var args , we can call it with 0 to n arguments.

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   Like         Discuss         Correct / Improve     var args  methods  method declarations  functions

 Q89. Do you see any problem with this code

public class BuggyBread {

   public static void main(String[] args) {
      method();
   }

   private static void method(String... args){
      for(String arg:args){
         System.out.println(arg);
      }
   }
}		Core Java
Ans. This will compile fine as we can provide 0 arguments for a var arg but will print nothing upon execution.

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   Like         Discuss         Correct / Improve     var args  methods  method declarations  functions

 Q90. Do you see any problem with this code

public class BuggyBread {

   public static void main(String[] args) {
      method("Hello");
   }

   private static void method(String... args){
      for(String arg:args){
         System.out.println(arg);
      }
   }

   private static void method(String arg){
      System.out.println(arg);
   }
}		Core Java
Ans. It will compile fine and the method call will bind to method with specific argument and not with var arg

i.e private static void method(String arg)

It will print "Hello" upon execution

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   Like         Discuss         Correct / Improve     var args  methods  method declarations  functions

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