30 Top Java 8 Interview Questions and Answers (2023)

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Intermediate / 1 to 5 years experienced level questions & answers

Ques 1. What is lambda expression?

Lambda expression is anonymous function which have set of parameters and a lambda (->) and a function body. You can call it function without name.

Structure of Lambda Expressions:

(Argument List) ->{expression;} or

(Argument List) ->{statements;}

For instance, the Runnable interface is a functional interface, so instead of:

Thread thread = new Thread(new Runnable() {

public void run() {

System.out.println("Hello World!");

}

});

Using Lambda you can simply do the following:

Thread thread = new Thread(() -> System.out.println("Hello World!"));

Functional interfaces are usually annotated with the @FunctionalInterface annotation - which is informative and does not affect the semantics.

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Ques 2. Given a list of employees, sort all the employee on the basis of age by using java 8 APIs only.

You can simply use sort method of list to sort the list of employees.

List<Employee> employeeList = createEmployeeList();

employeeList.sort((e1,e2)->e1.getAge()-e2.getAge());

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

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Ques 3. Given the list of employees, find the employee with name 'John' using Java 8 API.

Check the following code:

List<Employee> employeeList = createEmployeeList();

Optional<Employee> e1 = employeeList.stream()

.filter(e->e.getName().equalsIgnoreCase("Mary")).findAny();

if(e1.isPresent())

System.out.println(e1.get());

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Ques 4. Given a list of employee, find maximum age of employee using Java 8 API.

Check the following code:

List<Employee> employeeList = createEmployeeList();

OptionalInt max = employeeList.stream().

mapToInt(Employee::getAge).max();

if(max.isPresent())

System.out.println("Maximum age of Employee: "+max.getAsInt());

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Ques 5. Provide some examples of Intermediate operations.

Example of Intermediate operations are:

filter(Predicate)
map(Function)
flatmap(Function)
sorted(Comparator)
distinct()
limit(long n)
skip(long n)

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Ques 6. Provide some examples of Terminal operations.

Example of Terminal operations are:

forEach
toArray
reduce
collect
min
max
count
anyMatch
allMatch
noneMatch
findFirst
findAny

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Java 8 Interview Questions and Answers

Intermediate / 1 to 5 years experienced level questions & answers

Ques 1. What is lambda expression?

Ques 2. Given a list of employees, sort all the employee on the basis of age by using java 8 APIs only.

Ques 3. Given the list of employees, find the employee with name 'John' using Java 8 API.

Ques 4. Given a list of employee, find maximum age of employee using Java 8 API.

Ques 5. Provide some examples of Intermediate operations.

Ques 6. Provide some examples of Terminal operations.

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