java 8 interview questions

By | March 7, 2023

Describe the newly added features in Java 8?

Java 8 introduced several new features and enhancements to the language, some of which are listed below:

  1. Lambda Expressions: Lambda expressions allow you to write more concise and expressive code by providing a way to pass functions as arguments to methods. They are a form of anonymous function that can be used to implement functional interfaces, which are interfaces that have only one abstract method.
  2. Stream API: Stream API provides a way to process collections of data in a more functional style. It allows you to perform operations on streams of data, such as filtering, mapping, and reducing, which can be applied in a chain to perform complex operations on the data.
  3. Date and Time API: Java 8 introduced a new Date and Time API that provides a more robust and flexible way to work with dates and times. The new API supports date and time calculations, formatting, parsing, and time zones.
  4. Default methods in Interfaces: Java 8 introduced the ability to define default methods in interfaces, which allows you to add methods to interfaces without breaking existing implementations.
  5. Method References: Method references provide a way to refer to a method by its name instead of using a lambda expression. They are useful when you want to pass a method as an argument to a function.
  6. Optional class: The Optional class provides a way to represent values that may be absent. It allows you to write more expressive and robust code by avoiding null checks.
  7. Nashorn JavaScript Engine: Java 8 includes a new JavaScript engine called Nashorn, which provides a way to execute JavaScript code within a Java application. It is designed to be lightweight and efficient and provides seamless integration between Java and JavaScript.

These are just a few of the new features and enhancements introduced in Java 8. Overall, Java 8 brought significant improvements to the language, making it more expressive, functional, and easier to use.

What are functional or SAM interfaces?

Functional interfaces, also known as Single Abstract Method (SAM) interfaces, are interfaces in Java that have only one abstract method. Functional interfaces are used to define the signature of lambda expressions and method references, which provide a way to pass functions as arguments to methods.

In Java 8 and later versions, the @FunctionalInterface annotation was introduced to mark interfaces as functional interfaces. This annotation ensures that an interface has only one abstract method and can be used as a functional interface.

Here’s an example of a functional interface:

@FunctionalInterface

public interface MyFunctionalInterface {

    int calculate(int x, int y);

}

In this example, MyFunctionalInterface is a functional interface that defines a single abstract method calculation. This method takes two integer arguments and returns an integer value.

Functional interfaces are used extensively in Java 8’s new features such as lambda expressions, streams, and method references. By using functional interfaces, you can write more concise and expressive code, making it easier to read and understand.

 What are some standard Java pre-defined functional interfaces?

Java provides several pre-defined functional interfaces in the java.util.function package, which are used extensively in lambda expressions and other functional programming constructs. Some of the commonly used functional interfaces are:

  1. Predicate: A Predicate is a functional interface that takes a single argument and returns a boolean value. It is used to test a condition and returns true or false based on the result of the condition.
  2. Function: A Function is a functional interface that takes one argument and returns a result. It is used to apply a function to an argument and produce a result.
  3. Consumer: A Consumer is a functional interface that takes a single argument and returns no result. It is used to perform an action on the argument, such as printing or updating a value.
  4. Supplier: A Supplier is a functional interface that takes no arguments and returns a result. It is used to generate a value on demand.
  5. UnaryOperator: A UnaryOperator is a functional interface that takes a single argument and returns a result of the same type as the argument. It is used to perform an operation on the argument and return the result.
  6. BinaryOperator: A BinaryOperator is a functional interface that takes two arguments of the same type and returns a result of the same type. It is used to perform an operation on the two arguments and return the result.

These are just a few of the pre-defined functional interfaces in Java. Each interface is designed to perform a specific task and is used in different contexts depending on the requirements of the application.

What is the lambda expression in Java and How does a lambda expression relate to a functional interface?

A lambda expression is a concise way to define a functional interface in Java. It allows you to create a small, inline implementation of a functional interface without having to define a separate class or method.

A lambda expression consists of three parts: the parameter list, the arrow token, and the body. The parameter list specifies the parameters that the lambda expression takes, the arrow token separates the parameter list from the body, and the body contains the implementation of the functional interface.

Here is an example of a lambda expression:

MyFunctionalInterface f = (x, y) -> x + y;

In this example, MyFunctionalInterface is a functional interface that has a single abstract method calculate(). The lambda expression (x, y) -> x + y provides an implementation of this method that adds its two integer parameters x and y together and returns the result.

The lambda expression is related to a functional interface because it provides an implementation of the abstract method defined in the functional interface. In other words, the lambda expression is an implementation of the functional interface, and can be assigned to a variable of the functional interface’s type.

Lambda expressions are used extensively in Java 8’s new features, such as streams and method references, to provide a more concise and expressive way of working with functional interfaces. They allow developers to write more readable and maintainable code, and make it easier to work with functional interfaces in Java.

What is the basic structure/syntax of a lambda expression?

The basic structure of a lambda expression in Java consists of three parts: the parameter list, the arrow token, and the body. The general syntax of a lambda expression is as follows:

(parameter list) -> { body }

The parameter list specifies the parameters that the lambda expression takes, and can be empty, a single parameter, or multiple parameters separated by commas. If there is only one parameter, the parentheses around the parameter list can be omitted.

The arrow token (->) separates the parameter list from the body of the lambda expression.

The body of the lambda expression contains the implementation of the functional interface. The body can be a single expression or a block of code enclosed in curly braces. If the body is a single expression, the curly braces can be omitted.

Here are some examples of lambda expressions with different parameter lists and bodies:

() -> System.out.println(“Hello, World!”); // No parameters, single statement body

x -> x * x; // Single parameter, single expression body

(x, y) -> {

    int sum = x + y;

    System.out.println(“The sum is ” + sum);

    return sum; // Multiple parameters, block body

}

In each of these examples, the lambda expression defines an implementation of a functional interface. The first example defines an implementation of a functional interface that takes no parameters and returns void. The second example defines an implementation of a functional interface that takes a single integer parameter and returns its square. The third example defines an implementation of a functional interface that takes two integer parameters, calculates their sum, prints it to the console, and returns the sum.

 What are Supplier and Consumer Functional interfaces?

Supplier and Consumer are two common functional interfaces in Java that are used to represent functions that take no input and produce a value (Supplier) or take an input and produce no value (Consumer), respectively.

  1. Supplier: The Supplier functional interface represents a function that takes no arguments and returns a value of a specified type. It has a single method get() that takes no arguments and returns a value of the specified type.

Here is an example of a Supplier that generates a random integer between 1 and 100

Supplier<Integer> randomNumber = () -> (int) (Math.random() * 100) + 1;

int num = randomNumber.get(); // Generates a random integer

  1. Consumer: The Consumer functional interface represents a function that takes an argument of a specified type and returns no value. It has a single method accept(T t) that takes an argument of type T and returns void.

Here is an example of a Consumer that prints the elements of a list:

Consumer<List<Integer>> printList = list -> {

    for (int num : list) {

        System.out.println(num);

    }

};

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);

printList.accept(numbers); // Prints the elements of the list

In this example, the Consumer printList takes a List of integers as an argument and prints each element to the console.

Both Supplier and Consumer are commonly used in functional programming and in the new features introduced in Java 8, such as streams and method references. They provide a way to represent common functions in a concise and expressive way.

What is a Predicate interface?

The Predicate interface is a functional interface in Java that represents a function that takes an argument of a specific type and returns a boolean value. It has a single abstract method test(T t) that takes an argument of type T and returns a boolean value.

The Predicate interface is commonly used to test whether a given object satisfies a certain condition. For example, you can use a Predicate to filter elements in a list or stream that meet a certain criterion.

Here is an example of a Predicate that tests whether an integer is even:

Predicate<Integer> isEven = num -> num % 2 == 0;

boolean result = isEven.test(4); // Returns true

In this example, the isEven Predicate takes an integer as an argument and returns true if the integer is even, and false otherwise. The test() method is used to apply the Predicate to a given integer.

The Predicate interface also provides several default methods that can be used to combine Predicate instances or negate their results. These methods include and(), or(), negate(), and others.

Overall, the Predicate interface is a powerful tool for working with boolean conditions in Java, and is commonly used in functional programming and in the new features introduced in Java 8, such as streams and lambdas.

In Java 8, what is Method Reference?

Method reference is a shorthand syntax introduced in Java 8 that allows you to refer to a method of a class or an object, without invoking it. It is used to pass a method as an argument to a higher-order function, such as a lambda expression. Method references simplify code and make it more readable.

There are four types of method references in Java 8:

  1. Reference to a static method: You can reference a static method of a class by using the syntax ClassName::staticMethodName. For example, String::valueOf refers to the static method valueOf in the String class.
  2. Reference to an instance method of an object: You can reference an instance method of an object by using the syntax objectName::instanceMethodName. For example, System.out::println refers to the instance method println of the System.out object.
  3. Reference to an instance method of a class: You can reference an instance method of a class by using the syntax ClassName::instanceMethodName. For example, String::length refers to the instance method length of the String class.
  4. Reference to a constructor: You can reference a constructor of a class by using the syntax ClassName::new. For example, ArrayList::new refers to the constructor of the ArrayList class.

Method references can be used wherever a functional interface is expected. A functional interface is an interface that has only one abstract method. For example, the java.util.function package in Java 8 provides several built-in functional interfaces, such as Consumer, Supplier, and Predicate.

 What is the difference between Collection API and Stream API?

The Collection API and Stream API are both part of the Java standard library and are used for working with collections of data, but they have different purposes and functionality.

The Collection API provides a set of interfaces and classes for working with collections of objects, such as lists, sets, and maps. It provides methods for adding, removing, and manipulating elements in a collection, as well as for iterating over the elements.

The Stream API, introduced in Java 8, provides a functional approach to working with collections of data. It allows you to perform complex operations on collections of data, such as filtering, mapping, and reducing, in a concise and expressive way.

Here are some of the key differences between the Collection API and Stream API:

  1. Mutability: The Collection API is designed for mutable collections, where elements can be added, removed, or modified at any time. In contrast, the Stream API is designed for immutable collections, where operations on the data do not modify the original data source.
  2. Eager vs. Lazy: The Collection API is generally eager, meaning that it performs operations on the data immediately when they are called. In contrast, the Stream API is generally lazy, meaning that it defers the execution of operations until the data is actually needed.
  3. Intermediate vs. Terminal Operations: The Collection API provides methods for both intermediate and terminal operations on collections. Intermediate operations, such as filtering or mapping, return a new stream that can be further manipulated. Terminal operations, such as forEach or reduce, produce a final result. In contrast, the Stream API provides only intermediate and terminal operations, with the intention of chaining them together to create a pipeline of operations.

Overall, the Collection API is more focused on manipulation and management of collections, while the Stream API is more focused on processing and transforming data in a functional way. They are complementary and can be used together to achieve powerful and flexible data processing tasks in Java.

 What does the filter() method do? when you use it?

The filter() method is a higher-order function in Java that is used to filter elements from a collection based on a given predicate. It returns a new stream containing only the elements that match the specified condition.

When you use the filter() method, you pass a predicate as an argument, which is a functional interface that takes an element of the stream as input and returns a Boolean value. The filter() method applies this predicate to each element of the stream and returns a new stream containing only the elements for which the predicate returns true.

Here’s an example that demonstrates the use of the filter() method to filter even numbers from a list of integers:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

List<Integer> evenNumbers = numbers.stream()

                                    .filter(n -> n % 2 == 0)

                                    .collect(Collectors.toList());

System.out.println(evenNumbers); // Output: [2, 4, 6, 8, 10]

In this example, we first create a list of integers using the Arrays.asList() method. We then convert this list to a stream using the stream() method. We apply the filter() method to this stream and pass a lambda expression that checks if an integer is even. Finally, we collect the filtered elements into a new list using the collect() method.

The output of this program is a list containing only the even numbers from the original list.

The filter() method can be used with any collection that implements the java.util.Collection interface, such as List, Set, and Map. It is a powerful tool for working with collections and is commonly used in functional programming.

What is the difference between flatMap() and map() functions?

The flatMap() and map() functions in Java 8 are both used to transform elements in a stream, but they work in slightly different ways.

The map() function is a higher-order function that takes a function as an argument and applies it to each element in the stream. It then returns a new stream containing the results of the function applied to each element. The function passed to map() should return a single value.

Here’s an example of using map() to convert a list of strings to a list of their lengths:

List<String> words = Arrays.asList(“apple”, “banana”, “orange”);

List<Integer> wordLengths = words.stream()

                                 .map(String::length)

                                 .collect(Collectors.toList());

System.out.println(wordLengths); // Output: [5, 6, 6]

In this example, the map() function is used to apply the length() method to each element of the words list, which returns the length of each string. The resulting stream contains the lengths of each string, and the collect() method is used to convert the stream to a list.

The flatMap() function is similar to map(), but it takes a function that returns a stream as an argument. It then flattens the resulting streams into a single stream. This is useful when you have a stream of collections, and you want to flatten it into a single stream of elements.

Here’s an example of using flatMap() to flatten a list of lists:

List<List<Integer>> numbers = Arrays.asList(Arrays.asList(1, 2, 3), Arrays.asList(4, 5, 6), Arrays.asList(7, 8, 9));

List<Integer> flattened = numbers.stream()

                                  .flatMap(List::stream)

                                  .collect(Collectors.toList());

System.out.println(flattened); // Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]

In this example, the flatMap() function is used to convert the list of lists of integers into a single stream of integers. The flatMap() function takes the stream() method of each list and flattens them into a single stream. The resulting stream contains all the integers from all the lists, and the collect() method is used to convert the stream to a list.

In summary, the map() function is used to transform each element in a stream into a single value, while the flatMap() function is used to transform each element in a stream into a stream of values and then flatten those streams into a single stream.

What is the difference between intermediate and terminal operations on Stream?

In Java 8, Stream operations can be categorized as intermediate or terminal operations based on whether they return a Stream or not.

Intermediate operations are operations that take a Stream as input, perform some transformation on the elements of the Stream, and then return a new Stream as output. These operations do not produce any result on their own and do not modify the original source. Examples of intermediate operations include map(), filter(), flatMap(), distinct(), and sorted().

Terminal operations are operations that take a Stream as input, perform some operation on the elements of the Stream, and produce a result or side effect. These operations are the final step in the Stream pipeline and do not return a Stream as output. Examples of terminal operations include collect(), reduce(), forEach(), count(), and anyMatch().

The key difference between intermediate and terminal operations is that intermediate operations are lazily evaluated, meaning that they do not produce any result until a terminal operation is called. This allows for more efficient processing of large datasets, as only the required elements are processed at any given time.

In addition, it is important to note that each Stream can only be operated on once. After a terminal operation is called on a Stream, it cannot be used again. This means that if you want to perform multiple operations on a Stream, you need to create a new Stream for each operation.

In summary, intermediate operations on Stream are used to transform the elements of the Stream and return a new Stream, while terminal operations are used to perform some operation on the elements of the Stream and produce a result or side effect. Intermediate operations are lazily evaluated, and each Stream can only be operated on once.

What are the sources of data objects a Stream can process?

Streams in computer programming can process data objects from a variety of sources. The sources of data object that a stream can process depend on the programming language and the implementation of the stream. Here are some common sources of data objects that streams can process:

  1. Collections: Streams can process data objects from collections such as lists, sets, and maps. For example, in Java, you can create a stream from a list using the stream() method, like this: List<String> list = Arrays.asList(“a”, “b”, “c”); Stream<String> stream = list.stream();
  2. Arrays: Streams can also process data objects from arrays. In Java, you can create a stream from an array using the Arrays.stream() method, like this: int[] arr = {1, 2, 3}; Stream<int[]> stream = Arrays.stream(arr);
  3. I/O channels: Streams can process data objects from input/output channels such as files, network sockets, and pipes. For example, in Java, you can create a stream from a file using the Files.lines() method, like this: Stream<String> stream = Files.lines(Paths.get(“file.txt”));
  4. Generators: Streams can process data objects generated by functions or algorithms. In Java, you can create an infinite stream of numbers using the Stream.iterate() method, like this: Stream<Integer> stream = Stream.iterate(0, n -> n + 1);
  5. Database queries: Streams can also process data objects from database queries. For example, in Java, you can create a stream from a result set using the resultSet.stream() method, like this: ResultSet resultSet = statement.executeQuery(“SELECT * FROM my_table”); Stream<Row> stream = resultSet.stream().map(this::convertRow);

Overall, the sources of data objects that a stream can process are diverse and depend on the programming language and the implementation of the stream.

What are the most used Intermediate operations?

Intermediate operations in streams are operations that transform a stream into another stream. There are several intermediate operations available in most stream implementations, and the most commonly used intermediate operations include:

  1. filter(Predicate<T> predicate): This operation returns a new stream consisting of the elements of the original stream that satisfy the given predicate.
  2. map(Function<T, R> mapper): This operation returns a new stream consisting of the results of applying the given function to the elements of the original stream.
  3. flatMap(Function<T, Stream<R>> mapper): This operation returns a new stream consisting of the elements of the streams produced by applying the given function to the elements of the original stream.
  4. distinct(): This operation returns a new stream consisting of the distinct elements of the original stream, according to their natural order or using a provided comparator.
  5. sorted(): This operation returns a new stream consisting of the sorted elements of the original stream, according to their natural order or using a provided comparator.
  6. peek(Consumer<T> action): This operation returns a new stream that performs the specified action on each element of the original stream as elements are consumed from the resulting stream.
  7. limit(long maxSize): This operation returns a new stream consisting of the first maxSize elements of the original stream.
  8. skip(long n): This operation returns a new stream consisting of the elements of the original stream, discarding the first n elements.

These intermediate operations can be combined to perform complex transformations on streams, making them a powerful tool for data processing in programming languages that support them.

What is the most common type of Terminal operation?

Terminal operations in streams are operations that produce a result or a side-effect, and terminate the stream processing. There are several terminal operations available in most stream implementations, and the most common types of terminal operations include:

  1. forEach(Consumer<T> action): This operation applies the specified action to each element of the stream.
  2. count(): This operation returns the number of elements in the stream.
  3. collect(Collector<T,A,R> collector): This operation collects the elements of the stream into a new collection, using the specified collector.
  4. reduce(T identity, BinaryOperator<T> accumulator): This operation reduces the elements of the stream to a single value, using the specified identity and accumulator functions.
  5. min(Comparator<T> comparator): This operation returns the minimum element of the stream, according to the specified comparator.
  6. max(Comparator<T> comparator): This operation returns the maximum element of the stream, according to the specified comparator.
  7. anyMatch(Predicate<T> predicate): This operation returns true if any element of the stream matches the given predicate, otherwise false.
  8. allMatch(Predicate<T> predicate): This operation returns true if all elements of the stream match the given predicate, otherwise false.
  9. noneMatch(Predicate<T> predicate): This operation returns true if no elements of the stream match the given predicate, otherwise false.

These terminal operations can be used to produce a result from a stream or to perform a side-effect on the elements of a stream, making them a powerful tool for data processing in programming languages that support them.

What do you mean by saying Stream is lazy?

When we say that a stream is “lazy”, we mean that the stream does not perform any computation until it is necessary. In other words, the stream does not evaluate any intermediate or terminal operations until a terminal operation is called on the stream. This is in contrast to “eager” evaluation, where all computations are performed immediately.

For example, consider the following code snippet in Java:

List<String> words = Arrays.asList(“hello”, “world”, “goodbye”, “moon”);

Stream<String> stream = words.stream().filter(w -> w.startsWith(“h”));

In this code, we create a list of words and then create a stream from the list using the stream() method. We then apply the filter() method to the stream to obtain a new stream that contains only the words that start with “h”. At this point, no computation has been performed, because we have not yet called a terminal operation on the stream.

If we now call a terminal operation on the stream, such as forEach(), then the intermediate operations will be evaluated and the terminal operation will be performed on the resulting stream:

stream.forEach(System.out::println);

In this code, we call the forEach() method on the stream to print out each word in the stream that starts with “h”. At this point, the intermediate operation filter() is evaluated, and the terminal operation forEach() is performed on the resulting stream.

By delaying the evaluation of intermediate operations until a terminal operation is called, streams can avoid performing unnecessary computations and optimize the processing of large data sets. This is why streams are said to be “lazy”.

Can you convert an array to Stream? How?

Yes, you can convert an array to a stream in Java using the Arrays.stream() method.

Here is an example:

String[] words = {“hello”, “world”, “goodbye”, “moon”};

Stream<String> stream = Arrays.stream(words);

n this example, we have an array of strings called words. We convert this array to a stream using the Arrays.stream() method, which takes the array as its argument and returns a stream of the elements in the array. We then store the resulting stream in a variable called stream.

Once you have the stream, you can perform intermediate and terminal operations on it to process the data as needed.

stream .filter(w -> w.startsWith(“h”)) .forEach(System.out::println);

In this example, we use the filter() method to filter the elements in the stream to only include those that start with the letter “h”. We then use the forEach() method to print out each element in the resulting stream that satisfies the filter condition. Note that these operations are lazy and won’t be evaluated until we call a terminal operation, such as forEach().

What is the parallel Stream? How can you get a parallel stream from a List?

A parallel stream is a type of stream in Java that allows for parallel processing of data, using multiple threads to process the data in parallel. This can improve the performance of certain types of operations that can be parallelized, such as filtering, mapping, and reducing large data sets.

To create a parallel stream from a List in Java, you can use the parallelStream() method instead of the regular stream() method.

Here’s an example:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

Stream<Integer> sequentialStream = numbers.stream();  // create a sequential stream

Stream<Integer> parallelStream = numbers.parallelStream();  // create a parallel stream

In this example, we have a list of numbers and we create a sequential stream from the list using the stream() method. We then create a parallel stream from the same list using the parallelStream() method.

Note that creating a parallel stream does not guarantee that the operations will be executed in parallel. Whether or not the operations are executed in parallel depends on the characteristics of the data set and the operations being performed.

Also note that not all operations can be parallelized effectively, so it’s important to test the performance of your code when using parallel streams to determine if it actually provides a performance benefit.

What is the default method, and why is it required?

Default methods were introduced in Java 8 to enable the addition of new methods to existing interfaces without breaking backwards compatibility. Prior to Java 8, if a new method was added to an interface, all classes implementing that interface would need to be updated to implement the new method. This could be a significant burden in cases where the interface was widely used.

Default methods provide a way to add new functionality to an interface without breaking backwards compatibility. A default method is a method declared in an interface with a default implementation. This means that classes implementing the interface will inherit the default implementation of the method, but can override it if necessary.

The default keyword is used to declare a default method. Here is an example:

public interface MyInterface {

    default void myDefaultMethod() {

        // default implementation

    }

}

In this example, myDefaultMethod() is a default method. Classes implementing MyInterface will inherit the default implementation of this method, but can override it if necessary.

Default methods are required in Java 8 because they enable the addition of new functionality to existing interfaces without breaking backwards compatibility. This is particularly useful in cases where an interface is widely used and it is not feasible to update all classes that implement the interface.

What are static methods in Interfaces?

Static methods in interfaces were introduced in Java 8 to allow interfaces to have their own utility methods, without the need for implementing classes to provide their own implementations.

A static method in an interface is a method that is associated with the interface itself, rather than with any particular implementing class. This means that you can call a static method on the interface directly, without the need for an instance of an implementing class.

Here is an example of a static method in an interface:

public interface MyInterface {

    static void myStaticMethod() {

        System.out.println(“This is a static method in an interface.”);

    }

}

In this example, myStaticMethod() is a static method declared in the MyInterface interface. It can be called using the interface name, like this:

MyInterface.myStaticMethod();

Static methods in interfaces can be useful for providing utility methods that are related to the interface’s functionality, but do not require an instance of an implementing class. They can also be used to provide default behavior for static methods that are implemented by implementing classes.

Note that static methods in interfaces cannot be overridden by implementing classes, because they are not associated with any particular instance of the interface. They can be shadowed by a static method with the same signature in an implementing class, but this does not affect the behavior of the static method in the interface.

What is MetaSpace? How does it differ from PermGen?

Metaspace is a new memory space introduced in Java 8 that replaces PermGen (Permanent Generation) memory space used in earlier versions of Java.

Metaspace is used to store class metadata, such as the class name, modifiers, and annotations, and it grows automatically as the JVM loads classes. It is implemented as a native memory space, rather than as a part of the Java heap, which allows it to be managed more efficiently by the JVM.

PermGen, on the other hand, was a memory space used in earlier versions of Java to store class metadata and other internal JVM data. However, PermGen was known to cause problems in certain situations, such as when large numbers of classes were loaded dynamically at runtime, or when class metadata was retained for a long time. These problems could cause PermGen to fill up and lead to OutOfMemoryErrors.

Metaspace was introduced in Java 8 to address these problems by providing a more efficient and flexible memory space for class metadata. Unlike PermGen, Metaspace is not subject to a fixed size limit, and it can grow dynamically as needed. Additionally, Metaspace is automatically cleaned up by the JVM when it is no longer needed, which helps to avoid memory leaks and other problems.

In summary, Metaspace is a more efficient and flexible memory space for storing class metadata than PermGen, which was used in earlier versions of Java. Metaspace is implemented as a native memory space and can grow dynamically as needed, making it better suited to the dynamic class loading and retention requirements of modern Java applications.

What are the feature of the new Date and Time API in Java 8?

The new Date and Time API in Java 8 provides a number of new features and improvements over the old java.util.Date and java.util.Calendar classes. Some of the key features of the new API include:

Immutability: All of the classes in the new Date and Time API are immutable, which means that once created, their values cannot be changed. This makes them safer to use in multithreaded environments and reduces the risk of programming errors.

Improved precision: The new API provides better precision for date and time calculations, with support for nanosecond resolution.

Time zones: The new API provides improved support for time zones, with a range of new classes for working with time zones, including ZoneId, ZoneOffset, and OffsetDateTime.

Fluent API: The new API provides a fluent interface for building and manipulating date and time objects, which makes it easier to write readable and maintainable code.

Better date and time parsing and formatting: The new API includes a new DateTimeFormatter class that provides improved support for parsing and formatting dates and times, including support for localized formats.

Backward compatibility: The new API provides backward compatibility with the old java.util.Date and java.util.Calendar classes, making it easier to migrate existing code to the new API.

Overall, the new Date and Time API in Java 8 provides a range of new features and improvements that make it easier and safer to work with dates and times in Java applications. It is more precise, more flexible, and provides a more fluent and readable interface for working with dates and times.

What is an Optional class?

In Java 8, the Optional class was introduced to handle null values in a more efficient and safe way. Before Java 8, developers had to manually check if a reference was null to avoid NullPointerException errors.

The Optional class is a container object that may or may not contain a non-null value. It is designed to encourage the use of null checks and make it more explicit when a value might be null. The Optional class provides methods to check whether a value is present, retrieve the value if it is present, and retrieve a default value if the value is not present.

Here is an example of how to use the Optional class in Java 8:

 Optional<String> optional = Optional.ofNullable(someString);

if (optional.isPresent()) {

    String value = optional.get();

    System.out.println(“The value is ” + value);

} else {

    System.out.println(“The value is not present”);

}

In this example, someString is a string that may or may not be null. We create an Optional object from someString using the ofNullable method. We then check if the value is present using the isPresent method. If the value is present, we retrieve it using the get method. If the value is not present, we print a message indicating that the value is not present.

The Optional class provides a safer and more concise way to handle null values in Java 8, helping to reduce the risk of NullPointerException errors. 

What is Nashorn in Java 8?

Nashorn is a JavaScript engine introduced in Java 8. It is a lightweight high-performance JavaScript interpreter that runs on the Java Virtual Machine (JVM) and is based on the ECMAScript 5.1 standard. Nashorn is fully integrated into the Java Runtime Environment (JRE) and can be used to execute JavaScript code directly from within Java applications.

Nashorn provides several advantages over the previous JavaScript engine in Java, Rhino. Some of the benefits include:

  1. Improved performance: Nashorn is faster than Rhino and can handle larger JavaScript files.
  2. Better interoperability: Nashorn provides seamless integration between Java and JavaScript, allowing developers to use JavaScript code within Java applications and vice versa.
  3. Access to Java APIs: Nashorn allows JavaScript code to access Java APIs directly, making it easier to write hybrid applications that combine Java and JavaScript.
  4. Support for modern JavaScript features: Nashorn supports the latest JavaScript features, including lambda expressions, and provides better compatibility with popular JavaScript frameworks like Angular and React.

Here is an example of how to use Nashorn to execute JavaScript code from within a Java application:

import javax.script.*;

public class NashornExample {

    public static void main(String[] args) throws Exception {

        ScriptEngineManager manager = new ScriptEngineManager();

        ScriptEngine engine = manager.getEngineByName(“nashorn”);

        String script = “print(‘Hello, World!’)”;

        engine.eval(script);

    }

}

In this example, we use the ScriptEngineManager class to obtain a reference to the Nashorn engine, and then we execute a simple JavaScript program that prints “Hello, World!” to the console using the eval method.

 

 

 

 

 

 

 

 

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