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

Interview Questions and Answers - Order By Rating

Rarely asked as default methods have been introduced with Java 8.

Q91. Can we have a default method definition in the interface without specifying the keyword "default" ?

Core Java

Ans. No. Compiler complains that its an abstract method and hence shouldn't have the body.

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Q92. Can a class implement two Interfaces having default method with same name and signature ?

public interface DefaultMethodInterface {
default public void defaultMethod(){
System.out.println("DefaultMethodInterface");
}
}

public interface DefaultMethodInterface2 {
default public void defaultMethod(){
System.out.println("DefaultMethodInterface2");
}
}

public class HelloJava8 implements DefaultMethodInterface,DefaultMethodInterface2 {
public static void main(String[] args){
DefaultMethodInterface defMethIn = new HelloJava8();
defMethIn.defaultMethod();
}
}

Ans. No. Compiler gives error saying "Duplicate Default Methods"

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Q93. What If we make the method as abstract in another Interface ?

public interface DefaultMethodInterface {
default public void defaultMethod(){
System.out.println("DefaultMethodInterface");
}
}

public interface DefaultMethodInterface2 {
public void defaultMethod(){
System.out.println("DefaultMethodInterface2");
}
}

public class HelloJava8 implements DefaultMethodInterface,DefaultMethodInterface2 {
public static void main(String[] args){
DefaultMethodInterface defMethIn = new HelloJava8();
defMethIn.defaultMethod();
}
}

Ans. Even then the Compiler will give error saying that there is a conflict.

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Q94. What if we override the conflicting method in the Class ?

public interface DefaultMethodInterface {
default public void defaultMethod(){
System.out.println("DefaultMethodInterface");
}
}

public interface DefaultMethodInterface2 {
default public void defaultMethod(){
System.out.println("DefaultMethodInterface2");
}
}

public class HelloJava8 implements DefaultMethodInterface,DefaultMethodInterface2 {
public static void main(String[] args){
DefaultMethodInterface defMethIn = new HelloJava8();
defMethIn.defaultMethod();
}

public void defaultMethod(){
System.out.println("HelloJava8");
}
}

Ans. There won't be any error and upon execution the overriding class method will be executed.

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Q95. What will happen if there is a default method conflict as mentioned above and we have specified the same signature method in the base class instead of overriding in the existing class ?

Ans. There won't be any problem as the Base class method will have precedence over the Interface Default methods.

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Q96. If a method definition has been specified in Class , its Base Class , and the interface which the class is implementing, Which definition will be picked if we try to access it using Interface Reference and Class object ?

Ans. Class method definition is overriding both the definitions and hence will be picked.

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Q97. If a method definition has been specified in the Base Class and the interface which the class is implementing, Which definition will be picked if we try to access it using Interface Reference and Class object ?

Ans. Base Class Definition will have precedence over the Interface Default method definition.

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Q98. Can we use static method definitions in Interfaces ?

Core Java

Ans. Yes, Effective Java 8.

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Q99. Can we access Interface static method using Interface references ?

Ans. No, only using Interface Name.

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Q100. Can we have default method with same name and signature in the derived Interface as the static method in base Interface and vice versa ?

Ans. Yes , we can do that as static methods are not accessible using references and hence cannot lead to conflict. We cannot do inverse as Default methods cannot be overridden with the static methods in derived interface.

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Q101. Can we override compareTo method for Enumerations ?

Core Java

Ans. No. compareTo method is declared final for the Enumerations and hence cannot be overriden. This has been intentionally done so that one cannot temper with the sorting order on the Enumeration which is the order in which Enum constants are declared.

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Q102. Why can't we use this in static context ?

Core Java

Ans. Static methods can be called using instance references wherein this would have made sense but static method can also be called using Class name wherein this would mean nothing and hence forbidden.

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Not frequently asked as it was introduced with Java 8.

Q103. What is the @FunctionalInterface annotation ?

Core Java

Ans. This is an informative annotation that specify that the interface is a functional interface. A Function Interface has only one abstract method and many default methods. Compiler generates an error if the interface specified with the annotation doesn't abide by the specifications for functional interface.

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Frequently asked to fresh graduates and less experienced.

Q104. Why do we write public static void main ? Can we use some other syntax too for main ?

Core Java

Ans. 1. public is the access modifier that makes the method accessible from anywhere, static is the keyword that makes it accessible even without creating any object, void means it doesn't return anything , String args[] is the array of argument that the method receives.

2. If we use main without the string args , it will compile correctly as Java will treat it as just another method. It wont be the method "main" which Java looks for when it looks to execute the class and hence will throw

Error: Main method not found in class , please define the main method as:
public static void main(String[] args)

3. Main is not a keyword but a special string that Java looks for while initiating the main thread.

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Q105. Will this code compile ?

public class BuggyBread1{
abstract public void test();
}

Core Java

Ans. No. It will give the compilation error saying "The abstract method test in type BuggyBread1 can only be defined by an abstract class".

We need to declare the class abstract for it to have any abstract method.

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Q106. Will this Code compile ?

abstract public class BuggyBread1{
abstract public void test(){};
}

Core Java

Ans. No. This will give a compilation error saying "Abstract methods do not specify a body".

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Q107. Which Software Development methodology is being used in your current Job ?

General

Ans. We are using Agile methodology. I attend daily stand up where the development leads takes the status of assigned stories, achievements, any bottlenecks or challenges. We follow iteration of 2 weeks.

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Q108. What are the advantages and disadvantages of static variables and static methods ?

Core Java

Ans. Advantages

Can do meta object operations ( like validating something before creating objects , keep count of number of objects )

Can do operations which have nothing to do with objects but still you want them to be tied to Class.

Disadvantages

Commonly used to static variables sometime leads to problems due to access by different objects.

Are not tied to objects so doesn't reflect pure Object Oriented approach.

Needs to be synchronized so as to avoid update conflicts by mutiple objects and threads.

Some limitation in testing as not all frameworks have facility to mock them. Powermock has but Mockito doesnt

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Q109. When are static and instance methods resolved ? During compile time or Runtime ?

Ans. Static methods are resolved during compile time and hence they cannot participate in runtime polymorphism. Instance methods are resolved during runtime.

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Q110. How can we execute a Java class independently if it doesn't have a static main method ?

a. By initiating the flow in any of the static method
b. By initiating the flow in any of static block
c. By initiating the flow in any other instance method named as main
d. By initiating the flow in any other instance method named as main and making it final

Ans. By initiating the flow in any of static block

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Q111. Which of the following is false about main method ?

a. It should be declared public and static
b. it should have only 1 argument of type String array
c. We can override main method
d. We can overload main method

Core Java

Ans. We can override main method

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Q112. Difference between parameters and arguments ?

Core Java

Ans. Parameters are the variables that the method is expected to receive along with the method call. Arguments are the values which are passed on while calling the methods.

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Q113. Explain TDD or Test Driven Design ?

Design

Ans. TDD is a development process that involves short iterations: first an automated test case is written. Then, the code is written to pass that test, and finally one refactors the new code to acceptable standards.

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Q114. How are values passed in Java ? By value or reference ?

Core Java

Ans. Java only provides pass by value.

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Recently asked in Capital One.

Q115. What will happen if we call perform(null) ?

public void perform(Object obj) {
System.out.println("Object");
}

public void perform(Integer int) {
System.out.println("Integer");
}

Core Java

Ans. compiler will throws error as ambiguous methods

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Q116. In which cases , moving methods to utility class could be useful ?

Core Java

Ans. It could be worthy to move a method to util class if the method needs to be shared, doesn't require polymorphic behavior and need not be overridden in special cases.

Don't belong to one group through is-a relationship ( You can share through parent class method )

Don't implement a specific interface ( java 8 default methods )

Doesn't involve complex computing as you will be loosing the benefit of object state with just static method.

Doesn't require polymorphic behavior as static methods don't participate in runtime polymorphism.

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Q117. What is the use of MethodHandle ?

Ans. MethodHandle is a modern, more flexible, more typesafe way of doing reflection.

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Q118. Which of the following is false ?

Core Java

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

Core Java

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 ?

Core Java

a. Final

b. Static

c. Volatile

d. Transient

Ans.b. Static

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