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Interview Questions and Answers - Order By Newest

Q91. 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);
   }
}

Ans. Yes, it will give compilation error and java will complain about duplicate method. Java treat var args internally as arrays and hence would result in same byte code for both method's syntax.

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Q92. Will this code work

public class BuggyBread {

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

   private static void method(String[] arg){
      System.out.println(arg);
   }
}

What all possible changes we can make to method signature to make it work ?

Ans. It won't work as java won't find the method definition for method with 2 arguments.

We can either declare the method as

private static void method(String arg,String arg2)

or

private static void method(String... arg)

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Q93. Can we compile and execute a Java class without main method ?

Ans. No without main method can not be executed it will throw an error illegal start of type. Main method is the entry point of application.

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Q94. Why do we pass an array of strings to main method ?

Ans. Array of strings in the main method are the list of arguments or parameters which are sent to the application / program.

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Q95. Can we synchronize the run() method in Java?

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Q96. Is Runtime Polymorphism possible without Inheritance ?

Ans. Yes, Runtime Polymprohism requires either Class inheritance or Interface implementation.

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Q97. 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 ?

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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Q98. Can we mock static methods ?

Ans. Yes we can use PowerMock. With Mockito , we cannot mock static methods.

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Q99. In the Following code which foo will get called.

foo(Integer i){
}

foo(String s){
}

public static void main(){
passing foo(null);
}

Ans. ambiguity error

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Q100. What could be the reason for allowing private methods in java 9 ?

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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Q101. What is the default execution method in Java?

Ans. public static void main(String[] args)

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Q102. Are final methods faster than regular instance methods ?

Ans. Yes. As they cannot be overridden , there is no use of virtual table concept which is used for dynamic binding resolution.

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Q103. What is virtual table with respect to method overriding in Java ?

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Q104. How is the virtual method table implemented in Java?

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Q105. How many VTables are there for each class ?

Ans. There is one VTable for each class.

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Q106. Have you ever used java.util.Objects class ?

Ans. Yes, We are using requireNonNull method for validating if the object is null.

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Q107. What is method hiding in Java ?

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Q108. Which Java version supports Interface Default methods ?

Ans. Java 1.8 or Java 8

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Q109. Can we call a static method using reference currently pointing to null.

Ans. yes, we can.
exa: public class Java{
public static void main(String... args) {
JAva j= null;
j.greeting(); // call with null reference
}
public static void greeting() {
System.out.println("Hello World");
}
} // output: Hello World

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Q110. How can you verify if there were interactions with a static method using PowerMock ?

Ans. We can use PowerMockito.verifyStatic for this purpose

PowerMockito.verifyStatic(VerificationModeFactory.times(1));
<Class_Name>.<static_method_name>;

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Q111. in the following class:
class A {
void methoda(Object o) {
Sysout("Object");
}

void methoda(String s) {
Sysout("String");
}

public static void main(String []args) {
A a = new A();
a.methoda(null);
}
}

what will be printed?

Ans. String

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Q112. Can a method return more than one value at a time in Java ?

Ans. object / native type returned can only be one but an object can comprise of a array , collection or a group of different value types.

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Q113. What are inline functions ? Do we have inline functions in Java ?

Ans. Inline functions , just like C++ Macros is an optimized technique used by compiler to reduce the execution time. If the function is working on pre identified values ( which aren't resolved at runtime ), the function can execute the method and evaluate the outcome at compile time only instead of making a function call at runtime.

In Java, the optimizations are usually done at the runtime or JVM level. At runtime, the JVM perform some analysis to determine which methods to inline. Java compiler would never inline any method and there is no way in java for the developer to explicitly define inlining of methods as it's take intrinsically care of during runtime only.

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Q114. What are inline functions ?

Programming Language

Ans. Inline functions , just like C++ Macros is an optimized technique used by compiler to reduce the execution time. If the function is working on pre identified values ( which aren't resolved at runtime ), the function can execute the method and evaluate the outcome at compile time only instead of making a function call at runtime.

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Q115. why is "".equals(str); safer than str.equals("")?

Ans. str.equals("") this statement will throw NullPointerException if str is null where as "".equals(str) works fine even if str is null

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Q116. What is the use of defining equals , compareTo and hashcode methods in a class ? Where are they used ?

Ans. equals, compareTo and hashcode are of use when the objects are used within collections.

Equals helps with collections that helps maintaining only unique objects ( like Set )

compare and compareTo helps with collections that helps maintaining objects in order ( TreeSet, TreeMap etc )

hascode helps with collections that facilitates hash searching ( like hashSet, hashMap etc )

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Q117. What is the difference between method and function in Typescript ?

Ans. Method belongs to a class whereas function isn't. So the only difference is the scope in which they are defined.

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Q118. Which of the following is false ?

a. A Class cannot override both hashcode and equals method.

b. A class can override both hashcode and equals method.

c. A Class must override hashCode method if its overridding equal method.

d. A Class can override hashCode even if its not overridding equals method.

Ans.a. A Class cannot override both hashcode and equals method.

Q119. Which of the following is not true for abstract classes ? Reference

a. Abstract Class is only meant to be sub classed and not supposed to be instantiated.

b. Abstract class handlers can be used to handle derived class objects.

c. We can't have an abstract class without abstract methods.

d. Abstract class has member elements.

Ans.c. We can't have an abstract class without abstract methods.

Q120. Which of the following keyword is expected with main method declaration ?

a. Final

b. Static

c. Volatile

d. Transient

Ans.b. Static

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