Java Streams Interview Questions
Java Streams Interview Questions
Java Streams is a powerful feature introduced in Java 8 that allows developers to easily manipulate and process data in a collection. It provides a way to efficiently perform operations such as filtering, mapping, and reducing on a collection of objects. There are various interview questions on Java Streams that test the candidate's understanding of its concepts, usage, and performance. These questions may cover topics such as the differences between Stream and Collection, intermediate and terminal operations, lazy and eager evaluation, parallel processing, and handling exceptions. A thorough understanding of Java Streams is essential for any Java developer to efficiently work with data and write more concise and elegant code.
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1 - What are Streams in Java?
Streams in Java are a set of functions that allow us to manipulate collections of data in a declarative and functional way. It supports operations like filtering, mapping, and reducing to perform complex data processing tasks easily and efficiently.
2) What is the difference between a Stream and a Collection?
A Stream is not a data structure that stores elements, but instead it operates on the elements of a Collection or an array. Streams do not have a concrete implementation and are evaluated on demand, whereas Collections are eagerly evaluated.
3) How is a Stream created in Java?
A Stream can be created from any Collection using the stream() method, or from an array using the Arrays.stream() method. There are also specialized stream creation methods for generating infinite streams or streams from input/output streams.
4) What is a terminal operation in Streams?
A terminal operation is the final operation in a Stream that produces a result, such as forEach(), collect(), or reduce(). It is the action that makes the Stream actually process the data.
5) Can we reuse a Stream in Java?
No, once a Stream is used, it is considered consumed and cannot be reused. However, intermediate operations can be applied to the same Stream to create another Stream.
6) What is lazy evaluation in Streams?
Streams have a feature of lazy evaluation, which means they are not evaluated until a terminal operation is called. This allows for more optimized and efficient processing of data, as only the necessary elements are processed.
7) Can we parallelize Streams in Java?
Yes, Streams can be processed in parallel using the parallel() or parallelStream() methods. This allows for parallel execution of operations on different chunks of data, leading to improved performance in multi-core processors.
8) What are the main functional interfaces used in Streams?
The main functional interfaces used in Streams are Predicate, Consumer, Function, and Supplier. These interfaces allow for the implementation of lambda expressions to perform filtering, mapping, and reducing operations on streams.
9) Is it possible to create an infinite Stream in Java?
Yes, an infinite Stream can be created using the generate() or iterate() methods. However, we need to ensure that we use a limiting operation like limit() to avoid an infinite loop.
10) What is the difference between Stream and Parallel Stream?
A Stream operates sequentially, while a Parallel Stream is capable of utilizing multiple threads to process data in parallel. This can lead to improved performance for larger datasets.
11) What is the purpose of the Stream API in Java 8?
The Stream API was introduced in Java 8 to provide a more functional approach to data processing, making it easier to write concise and readable code.
12) How does the Stream API handle null values?
The Stream API does not allow null values and will throw a NullPointerException if a null element is encountered in a Stream.
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13) What is method reference in Streams?
A method reference in Streams is a shorthand notation for lambda expressions, which uses the existing methods as lambdas.
14) How can we convert a Stream back into a Collection?
We can use the collect() method with a Collector implementation to convert a Stream back into a collection, such as List, Set, or Map.
15) How is parallel sorting achieved using Streams?
Parallel sorting can be achieved using the parallelStream() method and the sorted() method with a Comparator or natural ordering. This allows for faster sorting of large datasets by utilizing multiple threads for parallel processing.
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