Java 8 Interview Questions and Answers

Functional interfaces are those interfaces that have a single functionality.

New features introduced in Java 8 are:-

• Introduction of Lambda Expression- first step to functional programming
• New stream API to support pipeline processing.
• Optional − Emphasis on handling null values properly.
• Nashorn Engine- Provides better performance than Rhino javascript engine.

Lamba expression is considered as the most significant feature of Java8. A Lambda expression provides functional programming, and that has simplified the code to a great extent. A lambda expression is fundamentally a function which can be created without belonging to any class.

Method references support in pointing to the methods by their names. A method reference is denoted by using "::" symbol. A method reference is used to indicate the following methods

• Static methods
• Instance methods
• Constructors using new operator (TreeSet::new)

This is a fundamental question in java 8 interview questions.

The valueOf() method converts data into human-readable form.So String valueOf() will return the string representation of the value. The valueOf() method is a static method.

• String valueOf(inum)--this syntax will return the string representation of the integer inum.
• String.valueOf(data, 0, 5)-- This syntax will return the string representation of the character Array 0 to 5
• String.valueOf(fNum) --this syntax will return the string representation of the float fNum

In java there a NullPointerException which can crash the code. It is complicated to remove the null checks from the code. Java 8 introduced Optional class in java. util package. Use of Optional class results in clean code without null checks. By using the Optional class, the programmer can specify the other value or other code to return. This makes the code more readable.

The default method implementation was introduced by Java 8 so that the old interfaces can use the lambda expression without implementing the methods in the implementation class.

The syntax for the Lambda expression is:-

parameter -> expression body

Characteristics of the Lambda Expression:-

• No need to declare the parameter type as the compiler will get the standard by the value of the parameter.
• For the multiple parameters parenthesis has to be declared, but for the simple parameter, parenthesis need not be declared.
• If a contains only a single parameter, then there is no need of curly braces.

Along with Java 8, a new improved engine Nashorn was introduced. Nashorn gives very high performance because it straightaway compiles the program code in the memory and then passes the bytecode to JVM. It uses the invoke dynamics feature of Java 7 to improve the performance.

A Spliterator is a type of Java8 Iterator in java. util package that traverses and partitions the elements of a source in Java into another Spliterator. A source can be a collection or an IO channel or a generator function

Java 8 introduced a command tool jjs for the Nashorn to execute the javascript program codes at the console.

The Stream API is used to process a group of objects. A stream is a series of objects which supports different methods that can be pipelined to produce the expected result.

The features of the stream are –

• A stream takes the input from the Collections, an Arrays or the I/O channels.
• Streams don’t alter the original data structure; they only give the result according to the pipelined methods.
• Each intermediate operation is executed in a lazy manner, and as a result, it returns a stream. Hence various intermediate processes can be pipelined. The terminal operations remain at the end of the pipelining process. It replaces the final value, and the pipeline is terminated.

Stream Pipelining is done by dividing the operations which can happen on the flow into two categories. The first is Intermediate operations and the second is Terminal operations. The common operations return the stream itself so that the result can be pipelined. The terminal operations remain at the end of the pipelining operation. It returns the final value, and the pipeline is terminated.

Random random = new Random();
random.ints().limit(15).forEach(System.out::println);

The code to print the count of empty strings in Java 8 is:-

List strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl");
//get a count of empty string
long count = strings.p
arallelStream().filter(string -> string.isEmpty()).count();

Point to be noted: Go through this Q&A very thoroughly as this is one of the most asked java 8 interview questions.

Parallel streams divide the provided venture into many and run them in unique threads, making use of a couple of cores of the computer. On the other hand, sequential streams work just like for-loop the use of a single core. The duties supplied to the streams are generally the iterative operations performed on the factors of a series or array or from different dynamic sources. Parallel execution of streams run more than one iterations concurrently in extraordinary accessible cores.

Collectors perform the reduction operations. It combines the result of the processing ongoing on the elements of the stream like collecting the elements into collections, summarizing the elements according to the different criteria. Collectors return the list or a string. As a result, the readability is increased. Static import used here is static import java.util.stream.Collectors.*;

In new data-time API, one of the class is Local Date-Time API where there is no problem of handling of the time-zones. Programmers use this API where time zones are not required. Local Date-Time API is defined in the package java.time

The Chrono unit was added in Java 8 to replace those integer value that was used in old API to represent the month, day, year, etc. unit is defined in the java.time.temporal.ChronoUnit

Type inference is a feature of Java that gives the capability to the compiler to seem at each method invocation and corresponding announcement to determine the type of arguments. Java provides multiplied model of type inference in Java eight