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6 Questions to Ask About the Streams API (With Sample Answers)

6 Questions to Ask About the Streams API (With Sample Answers)

Streams API is a set of tools for working with groups of things that need to be done in a certain order. If you’re interviewing for a technical job, like software engineer, you might be asked questions about this Java 8 component to see how well you can use it. Reviewing some questions about this tool can help you figure out what you should know for your interview and give you time to plan answers that will make a good impression on a potential employer. This article talks about six possible Streams API interview questions and shows you how to answer them.6 Questions to Ask About the Streams API (With Sample Answers)

There are 6 questions about the Streams API and examples of how to answer them.

Here are some common questions about the Streams API that you might be asked in an interview:

What is the Stream API in Java?

This question might be asked at the beginning of a job interview to find out how well you know Stream API. In your answer, give a clear explanation of what Stream API is and how it works. You should also write down some of the benefits of using this set of tools.

Example: “The Stream API is a set of tools that were added to Java 8 to make it easier to deal with the order of elements. With this feature, you can get rid of a lot of code that does the same thing over and over and make an app work better. It also makes programmes easier to read and lets us process a lot of data at once.”

What does the map() function in Java do?

It’s important to know how to use the different functions of Java if you want to get a technical job. This is a question an interviewer might ask to find out if you have done different jobs before and if you could do them in the new role. Explain what the map() function does and how to use it.

Example: “With Java’s map() function, objects of one type can be changed into objects of another type. This function could be used to turn a List of Strings into a List of Integers. To do this, I would give all of the List of String items a function, like parseInt(), that they would all use. A list of integers is what would come out of it.”

How are a collection and a stream different from each other?

During your interview, you might be asked to compare and contrast two common Streams API terms or ideas. This shows the employer that you know what each term means and how it is different from other terms. Pick a few things that make a collection different from a stream. You may want to say why you think one is better.

Example: “There are different ways to use both collection and stream. Collections are used to store and change a group of data, while streams are used to process data. Collections are better than streams because you can take things out or add new ones. You can’t change streams in any way. Iterations in collections happen across the whole collection, while iterations in streams happen inside the stream.”

What does the filter() method do? What could you do with it?

An employer can find out if you know how to use the filter() function by asking you this question. You need to explain why the filter() method is used to answer this question. Also, give an example of when and why it would work.

Example: “You can do something to elements that meet a condition you set up in a Predicate function using the filter() method. For instance, if I had a List of Integers and wanted to make a list of even integers, I could use the filter() function to check if values are even or odd. Then, the filter could pick out the elements that fit this condition.”

5. Can an array be changed into a stream? How?

Interviewers may ask you about what you can and can’t do. Listen carefully to make sure the Streams API can help you do it. Tell the employer that you can change an array into a stream and explain how you can do this. There are a lot of ways to do this, so pick one or explain a few of them briefly.

Example: “Yes, you can turn an array into a stream. To do this, you would use the toArray() method, which would give me an object array with all of the stream’s elements. You can also use the collect() method to turn a stream into a list, which is useful if you want to keep the order of the elements.”

6. What kinds of Stream operations are there? What are their names?

This question checks how well you know how Java divides up Stream operations. In your answer, tell how many Stream operations there are and what they do in a few words. You can also talk about how Java separates intermediate operations into those that don’t keep track of state and those that do.

Example: “There are two main kinds of stream operations. There are things to do at the beginning and at the end. Terminal operations like IntStream.sum and Stream.forEach can move through the stream and have a side effect. Once you’ve done these things to the streamline pipeline, you can’t use it anymore. But intermediate operations are always lazy, so you can’t just add them to the Stream pipeline and have them work.


“When an intermediate operation is run, the data is not filtered. It makes a new stream instead. This has the first stream’s elements that match the given predicate when the stream is walked through. Java divides intermediate operations into those that don’t change the state and those that do. When they change an element into a new element, stateless operations don’t remember the state of an element they’ve already seen. Stateful operations use the state of elements they have already seen, but unlike stateless operations, they have to process the whole input before they can give a result.”

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