java 8 interview questions: 33 Java 8 Interview Questions (With Example Answers)


Answers ( 2 )


    In this article, we will discuss Java 8 interview questions and answers. We have provided some example answers for each of these questions for reference.

    What is the difference between the following?

    • String, Object and StringBuilder are in java.lang package
    • Integer, Long and Double are in java.lang package

    What is a lambda expression?

    A lambda expression is a block of code that can be passed around and executed later. It’s like an anonymous function, but with more flexibility because you can assign the value to a variable or pass it as an argument to another method.

    Lambdas are useful when you have a piece of code that you need to use repeatedly, but don’t want to create an entire class just for one method. For example:

    • If you want to sort all numbers in an array from smallest to largest, instead of creating a new class called SortableNumbers and making all your numbers implement the Comparable interface (which requires writing lots of boilerplate), you could use this lambda expression instead:

    sort(numbers) -> (num1, num2) -> num1 < num2 ? -1 : 1

    What’s the difference between an interface and an abstract class?

    An interface is a contract that defines the behavior of something. It can have methods, but they must be abstract (i.e., they have no implementation).

    An abstract class is a class with one or more abstract methods. Abstract classes can also have non-abstract methods, which means you can use them directly in your code instead of extending them from other classes or interfaces like you do with interfaces.

    Interfaces are extended by other interfaces, whereas abstract classes are extended by other abstract classes only–you cannot extend an interface directly; it has to be extended first before being used as an extension point for another class or interface!

    Why should you prefer a single-method interface over inheritance in most cases?

    A single-method interface is a great way to define an interface for your own application. It’s more focused, so it’s easier to implement and use. Another benefit of implementing a single-method interface is that you can use it as the parameter type in other methods, which makes it easier to test those methods.

    How do you resolve conflicts between two annotations with the same name?

    The first thing to consider is the priority of each annotation. If two annotations have the same name and different priorities, then they are in conflict. For example:

    @Annotation(priority = 1) @Annotation(priority = 2) @interface MyAnnotation {}

    If you assign a value to one of these, it will override any other occurrence of that annotation with a lower priority or no value specified at all.

    For example: @MyAnnotation(“foo”) public void foo() {}

    What is the difference between Comparator and Comparable<?>?

    A Comparator is a functional interface that allows you to compare objects for equality. The Java language provides several implementations of this interface, including java.util.Comparator and java.util.Collections#naturalOrder(). Comparators are often used with the sort() method of Arrays or Collections classes, which sorts an array or collection based on its elements’ natural ordering (see https://docs-javaee8api-8-1/javax/servlet/ServletRequest).

    A Comparable object allows you to compare objects for equality and sort those objects if they implement the interface.

    Can you use Java 8 lambda expressions to override methods?

    Lambda expressions can be used as a method argument, method return value, and as the body of a method. A lambda expression can also be passed as an argument to another method or constructor that takes one or more parameters.

    A lambda expression without any parameter list is a functional interface on its own and it can be used to override methods in Java 8.

    Does primitive types need modifiers like public, private, protected before them when used within a class or method definition?

    No, primitive types do not need modifiers like public, private and protected before them when used within a class or method definition. This is because they are not reference types. Primitive types are simple data structures that cannot be assigned to anything else but themselves. For example:

    In this case, the integer variable i does not have any scope restrictions as it is declared inside the main() method which is an unrestricted access level for all variables defined within it (no modifier required).

    How does Java define null for reference types or null for primitive types ?

    • null is used to represent the absence of a value.
    • Java defines null for reference types and primitive types differently.
    • null is a keyword in Java.
    • It’s a primitive value in Java, but an object when we use it in our code.

    When does a class become eligible for garbage collection?

    • When the class is no longer referenced by any other object.
    • If the class is not declared final, static, or abstract.
    • If it has no instance variables (instance variables are defined using the keyword “this”).
    • If it has no methods (methods are defined using a method declaration).

    How will you calculate memory usage of an object in Java?

    The memory usage of an object in Java is calculated by adding the memory usage of all its fields.

    So, if you’re looking to get a job in Java development and would like to ace your interview with these 33 questions, then we strongly recommend that you practice as much as possible beforehand. The more prepared you are when facing these questions from an interviewer – the better chance you have at getting hired!


    java 8 interview questions: 33 Java 8 Interview Questions (With Example Answers)


    As we all know, Java 8 is the latest version of Java. It’s been around for a while now but still, developers are not using it as much as they should be because they are either unaware of its features or do not know how to use them properly. You might have heard about lambdas and method references but you might not know how to use them practically. In this article, I will cover some important topics related to lambda expressions in Java 8 such as why was it developed?, what kind of benefits does it provide over other versions (Java 7 and earlier)? etc etc..

    Why was Java 8 developed?

    Java 8 was developed to add new features to the Java language.

    • It was made more functional by introducing lambda expressions and Streams.
    • It made it more object oriented by adding default methods in interfaces, static methods in interfaces and also default constructors for classes.
    • The modularity feature of java 8 allows you to create your own module(s) which can be used with other modules without having any conflict with each other

    What is Lambda expression?

    Lambda expressions are a functional interface in Java 8. They allow you to define and execute a function in a single expression. Lambda expressions are anonymous functions, which means that they cannot be named and used outside their defining class.

    Lambdas can be used wherever a method is expected–for example, as arguments of methods or as return values from methods. A lambda expression has the following form:


    (parameters) -> expression;“`

    Which kind of benefits does Java 8 provide over its previous versions (Java 7 and earlier)?

    Java 8 provides several benefits over its previous versions (Java 7 and earlier). The most important ones are:

    • More concise and readable code. Java 8 introduces lambda expressions, which are used for writing concise code that is easier to read than traditional methods and classes. In addition, you can use streams as an alternative to loops when performing operations on collections of data.
    • Less boilerplate code. You no longer need to write lots of getters/setters or constructors with only one line of code! Instead, use autoboxing and auto-unboxing features provided by Java 8 so that you don’t have to worry about boxing/unboxing objects manually anymore when assigning them values from primitives such as ints or doubles etc…

    Is it possible to write lambda expressions in older versions of Java?

    Yes, it is possible to write lambda expressions in older versions of Java. However, the syntax will be different.

    The syntax will be similar to anonymous inner classes or method references.

    What all syntaxes are allowed for writing lambda expressions?

    You can write a lambda expression in the following syntaxes:

    • No explicit return type, e.g., (Integer x) -> { System.out.println(x); }
    • Explicitly specifying a functional interface and an implementation of that interface, e.g., () -> { System.out.println(“Hello World”); } or (String s) -> { System.out.println(s); }
    • Explicitly specifying an abstract class and implementing its methods in the body of your lambda expression, e.g., () -> new MyClass().sayHi()

    How many ways are there to define a functional interface in Java?

    You can define a functional interface in Java by defining a single abstract method.

    You can also define it by defining a single abstract method and a default implementation of that method.

    Or you could define multiple abstract methods, and then provide an implementation for each one of them (or just one).

    What is method reference? Why use it when we already have lambda expression?

    In the Java 8 release, a new feature has been added to the language called method references. The purpose of this feature is to allow you to refer to an existing method from within your code, without having to create a lambda expression.

    The syntax for using a method reference is similar in style and form as lambda expressions:

    Object result = String::length();

    This line of code will return the length of any String object passed into it as an argument (or throw an exception if there isn’t one).

    When should we use lambda expressions over method references?

    Lambda expressions can be more readable than method references.

    • When the lambda expression is more readable than the method reference, we should use a lambda expression. For example, in the following code snippet, we can see that it’s easier to understand what’s happening when we use a lambda expression:

    public void print(String s) { System.out.println(s); } public static void main(String[] args) { print(“Hello World”); }

    Which is the most common use case for lambda expressions in Java 8? For example, which type of code you will use it for most often? A few examples would be enough.

    You can use lambda expressions to create methods that can be passed to other methods. For example, you may want your code to sort an array of objects by some criteria, but you don’t know how it should be sorted. Instead of writing a separate sorting method, you could just pass in a lambda expression that defines how each element should be sorted and let Java do the rest!

    This type of use case is common because it allows us programmers to reuse code by passing around pre-defined functions (or “lambdas”) instead of having them hardcoded into our program.

    Does Java 8 support method overloading in combination with lambdas, i.e. having multiple methods with same name but different parameter types or number of parameters etc.? If yes, how can one make sure that he/she has used the right method among them during runtime without any explicit look-up mechanism in place (like scoping rules)? If not then why not? Does it mean that one need to write extra code (i.e., using reflection) to get it done at runtime or there is some other way available which I am missing here?

    In Java 8, method overloading is supported in combination with lambdas. For example:

    // Method overloading in combination with lambdas

    public class MyClass{

    public static void main(String[] args){ MyClass obj = new MyClass();; // calls foo() from java.lang.Object; // calls bar() from java.lang.Object }

    • A method may have multiple signatures as long as each signature has a unique set of parameter types and/or number of parameters (including their order). The compiler determines which signature should be called based on the type(s) used when invoking the method at runtime.*


    This is a great question, and one that many Java developers have asked. The answer is yes, it is possible to use method overloading with lambda expressions in Java 8. You can do this by specifying the type of parameter used in each method’s signature. For example:

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