Part 12
Core java interview questions and answers for 3-5 years experience covered in this post:
1.
Will the child interface functional
interface?
|
1. @FunctionalInterface
public interface
Parent {
public void
add();
}
@FunctionalInterface
public interface
Child extends
Parent {
}
2.@FunctionalInterface
public interface
Parent {
public void
add();
}
@FunctionalInterface
public interface
Child extends
Parent {
public void
add();
}
3.@FunctionalInterface
public interface
Parent {
public void
add();
}
@FunctionalInterface
public interface
Child extends
Parent {
public void
substract();
}
4.@FunctionalInterface
public interface
Parent {
public void
add();
}
public interface
Child extends
Parent {
public void
substract();
} |
- Case 1: If an interface extends functional interface and the child
interface doesn’t contain any abstract method, then the child interface is
always a functional interface.
- Case 2: In the child interface we can define exactly the same parent
interface abstract method.
- Case 3: In the child interface we can’t define any new abstract method
then we will get a compile-time error.
- Case 4: Child interface doesn’t declare FunctionalInterface then code will compile.
 
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What is the difference between
Annonymous Inner class and Lambda Expression?
|
|
Annonymous Inner class |
Lambda Expression |
|
1. |
It is a class without a name. |
It is a function without a name. |
|
2. |
An anonymous inner class can extend an abstract class or concrete
class. |
Lambda expression cannot extend an abstract class or concrete
class. |
|
3. |
An anonymous inner class can implement an interface that has
multiple abstract methods as well as a functional interface. |
Lambda expression can implement only a functional interface. |
|
4. |
Inside the inner class, we can declare an instance variable. |
Inside lambda expression, we can declare only local variables. |
|
5. |
An anonymous inner class can be instantiated. |
Lambda expression cannot be instantiated. |
|
6. |
An anonymous interface is the best choice if we want to handle
multiple methods. |
Lambda expression is the best choice if we want to handle the
interface with a single abstract method. |
|
7. |
Inside the Anonymous inner class, ‘this’ always refers current
anonymous inner class object but not the outer class object. |
Inside lambda expression, this always refers current outer class
object. |
|
8. |
For an anonymous inner class at the time of compilation, a
separated .class file will be generated. |
For the lambda expression, separate .class file won’t be
generated. |
What are default methods? What is the
basic purpose of default methods?
- Methods defined inside interface with default keyword is called default
method.
- Since, Java 8 you can have method implementation inside the interface.
- Default methods can be used for backward compatibility.
- In the regular case, if you declare or add a new method in the interface
then million of code may break so avoiding this situation, we can add a
default method inside the interface so no code will be affected.
- Please refer to the below example.
|
package simplifiedjava.crackedInterview.java8; public interface InterfaceForDefaultMethod {
default void
m1() {
System.out.println("m1() from DefaultMethodDemo interface is called");
} } package simplifiedjava.crackedInterview.java8; public class DefaultMethodDemo implements InterfaceForDefaultMethod{
public static void
main(String[] args) {
InterfaceForDefaultMethod demo = new
DefaultMethodDemo();
demo.m1();
DefaultMethodDemo demo1 = new
DefaultMethodDemo();
demo1.m1();
}
}
Output:
m1() from DefaultMethodDemo interface is called
m1() from DefaultMethodDemo interface is called |
How will you uniquely call same methods
declared in multiple interfaces? If Inteface A has add() and
interface B also have add() then how will you differentiate both
methods?
- Please refer below example.
|
package simplifiedjava.crackedInterview.java8; public interface Left {
default void
m1() {
System.out.println("Left m1() called.");
} } package simplifiedjava.crackedInterview.java8;
public interface
Right {
default void
m1() {
System.out.println("Right m1() called.");
} } package simplifiedjava.crackedInterview.java8; public class LeftRightInterfaceDemo implements Left, Right{
public static void
main(String[] args) {
LeftRightInterfaceDemo demo = new
LeftRightInterfaceDemo();
demo.m1(); }
@Override
public void
m1() {
Left.super.m1();
Right.super.m1();
}
}
Output:
Left m1() called.
Right m1() called. |
How will you invoke default methods from class?
- First, you need to declare the default method in the interface.
- Second, you have to create one class and implement that interface that has
the default method.
- Then, simply instantiate the class and with the class reference variable,
you can call default methods.
- Please refer to the below example.
|
package simplifiedjava.crackedInterview.java8; public interface InterfaceForDefaultMethod {
default void
m1() {
System.out.println("interface m1() method called.");
} } package simplifiedjava.crackedInterview.java8; public class DefaultMethodDemo implements InterfaceForDefaultMethod{
public void
m1() {
System.out.println("Class m1() method called."); }
public static void
main(String[] args) {
InterfaceForDefaultMethod demo = new
DefaultMethodDemo();
demo.m1();
DefaultMethodDemo demo1 = new
DefaultMethodDemo();
demo1.m1();
}
}
Output:
Class m1() method called.
Class m1() method called.
|
What are the static methods in
functional interface?
- Static method declared inside the interface is called the
static method.
- We can have the implementation of static class inside the
interface.
- Static methods can invoke with the Interface name. No need to instantiate the class.
What is the purpose of static methods
in functional interface?
- Just to define utility methods in the interface then we can go for static
methods.
- The main purpose of the static method is, we can invoke static methods like
the utility class method. No need to create an instance of that class.
What are the static methods defined in
Predicate functional interface?
- Predicate has defined isEqual () static method inside it.
- Please refer to the below example for syntax.
|
package simplifiedjava.crackedInterview.java8; import java.util.function.Predicate; public class PredicateStaticMethodDemo {
public static void
main(String[] args) {
Predicate<String> p
= Predicate.isEqual("Java");
System.out.println(p.test("java"));
System.out.println(p.test("Java"));
System.out.println(p.test("Databse"));
}
}
Output:
false
true false |
Wap to implement Predicate
interface?
|
package simplifiedjava.crackedInterview.java8;
import
java.util.ArrayList;
import
java.util.List; import java.util.function.Predicate; public class FindPositiveOrNegativeNoUsingPredicate { public static void main(String[] args) {
List<Integer> list = new
ArrayList<Integer>();
list.add(-10);
list.add(20); list.add(30); Predicate<Integer> p = no -> no > 0;
for(Integer i : list) {
if(p.test(i)) {
System.out.println("Positive Number");
}else {
System.out.println("Negative Number");
}
}
}
}
Output:
Negative Number
Positive Number
Positive Number |
WAP to implement Function
interface?
|
package simplifiedjava.crackedInterview.java8; import java.util.function.Function; public class FunctionInterfaceDemo {
public static void
main(String[] args) {
Function<String, Integer> f = s
-> s.length();
System.out.println(f.apply("Simplify Java"));
}
}
Output: 13 |
- Java interview questions and answers all MNC - Click here
- Basic core java interview questions and answers for freshers - Click here
- Core java interview questions for 3 years experience - Click here
- Core java interview questions and answers for 3-5 years exp - Click here
- Core java interview questions and Answers for 5 - 7 Years exp - Click here
- Basic Java Interview Questions and Answers - Click here
- Java interview questions and answers on oops - Click here
- Java interview questions and answers on Strings - Click here
- Java interview questions on exception handling - Click here
- Interview questions on multithreading in java for experienced - Click here
- Interview questions on serialization in java for experienced - Click here
- Interview questions on inner class in java for experienced - Click here
- Interview questions on Collections in java for experienced - Click here
Upcoming questions in next post:
121. What are the static method defined in Function functional interface.
122. What is the difference between Predicate and Function interface.
123. What is Consumer functional interface?
124. What is the abstract method defined in Consumer functional interface.
125. What are the default methods defined in Consumer functional interface.
126. What is Bi-Consumer functional interface.
127. What is the abstract method defined in Supplier functional interface.
128. What are the default methods defined in Supplier functional interface.
129. What are the static method defined in Supplier functional interface.
130. What is the difference between Predicate and Bi-Predicate.
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Thank you techies for visiting this blog. I hope you enjoyed this blog and got more technical knowledge. I have tried to cover all types of questions and provided examples tested on eclipse as much as I can. Guys, please don’t just mug up the questions and answers. Try to clear your concepts with examples. Try to write a code on eclipse once you read the concepts. It will help you to memorize the concepts for a very long time. Simultaneously you will be prepared for interview programs as well. It will help you to survive in the IT sector for a long time. It may be easy to crack an interview but it's really tough to survive in the IT industry with inadequate knowledge and skills. I have collected all the questions from actual interviews attended by my friends, colleagues, college mate and classmate. I have covered frequently asked questions as well as challenging questions. I have included many programs to understand the concept thoroughly. I will try to explain the concept with the help of a real-time program in eclipse. You can share more questions which are not covered in this blog or post. Always welcome your suggestions and queries. I will definitely try to resolve it. Please comment your queries and new set of questions under the comment sections. I will create a new post for those questions.
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