Java Streams API tutorial

Description java streams api

java streams API tutorial is Functional programming is becoming very popular and it focuses on pure functions. Functional applications avoid the shared state and tend to be more concise and predictable than those using object-oriented code. In this course, Nelson will teach you how to move away from imperative to declarative programming allowing you to write less code and focus on what is important when building applications.

The features of Java stream are –

  • A stream is not a data structure instead it takes input from the Collections, Arrays or I/O channels.
  • Streams don’t change the original data structure, they only provide the result as per the pipelined methods.
  • Each intermediate operation is lazily executed and returns a stream as a result, hence various intermediate operations can be pipelined. Terminal operations mark the end of the stream and return the result.

Different Operations On Streams-
Intermediate Operations:

  1. map: The map method is used to returns a stream consisting of the results of applying the given function to the elements of this stream.
    List number = Arrays.asList(2,3,4,5);
    List square =>x*x).collect(Collectors.toList());
  2. filter: The filter method is used to select elements as per the Predicate passed as argument.
    List names = Arrays.asList("Reflection","Collection","Stream");
    List result =>s.startsWith("S")).collect(Collectors.toList());
  3. sorted: The sorted method is used to sort the stream.
    List names = Arrays.asList("Reflection","Collection","Stream");
    List result =;

Terminal Operations:

  1. collect: The collect method is used to return the result of the intermediate operations performed on the stream.
    List number = Arrays.asList(2,3,4,5,3);
    Set square =>x*x).collect(Collectors.toSet());
  2. forEach: The forEach method is used to iterate through every element of the stream.
    List number = Arrays.asList(2,3,4,5);>x*x).forEach(y->System.out.println(y));
  3. reduce: The reduce method is used to reduce the elements of a stream to a single value.
    The reduce method takes a BinaryOperator as a parameter.List number = Arrays.asList(2,3,4,5);
    int even =>x%2==0).reduce(0,(ans,i)-> ans+i);

List of topics for java streams

  • What is functional programming ?
  • Stream API
  • Transformations with Map
  • Reduce
  • Filter
  • Collectors
  • Statistics
  • Grouping

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