OpsTree Solutions Interview Questions and Answers

Using Java 8 Streams API to print single occurrences of names in an ArrayList of Strings.

• Use stream() method on the ArrayList to create a stream of elements.

• Use filter() method to filter out elements that occur more than once.

• Use distinct() method to get only unique elements.

• Use forEach() method to print each unique element.

Reverse the year of birth and name, then print them in that order.

• Reverse the year of birth using StringBuilder.reverse() method

• Reverse the name using StringBuilder.reverse() method

• Print the reversed year of birth followed by the reversed name

Code to print each name and the number of occurrences in an ArrayList of Strings.

• Iterate through the ArrayList and use a HashMap to store the count of each name.

• Print each name along with its count from the HashMap.

Interfaces and Abstract classes in Java are used for achieving abstraction and defining contracts for classes to implement.

• Interfaces in Java are like blueprints for classes, defining methods that must be implemented by classes that implement the interface.

• Abstract classes are classes that cannot be instantiated and can have both abstract and concrete methods.

• Example of an interface in Java: public interface Shape { double calculateArea(); double calculatePerimeter(); }

• Exampl...read more

Lambda expressions in Java are a concise way to represent anonymous functions.

• Lambda expressions are used to provide implementation of functional interfaces.

• They enable you to treat functionality as a method argument, or code as data.

• Syntax: (parameters) -> expression or (parameters) -> { statements; }

• Example: (int a, int b) -> a + b

Functional interfaces in Java are interfaces with only one abstract method, used for lambda expressions and functional programming.

• Functional interfaces have only one abstract method, but can have multiple default or static methods.

• They are used for lambda expressions and functional programming in Java.

• Examples include java.lang.Runnable, java.util.Comparator, and java.util.function.Function.

Threads in Java are lightweight sub-processes that allow concurrent execution within a single process.

• Threads allow multiple tasks to be executed simultaneously in a Java program.

• Threads share the same memory space and resources within a process.

• Example: Creating a new thread using the Thread class or implementing the Runnable interface.