Terminal and intermediate stream methods in Java

Terminal stream methods

  • findFirst() returns the first element;
  • findAny() returns any matching element;
  • collect() presenting results as collections and other data structures;
  • count() returns the number of elements;
  • anyMatch() returns true if the condition is met for at least one element;
  • noneMatch() returns true if the condition is not met for any element;
  • allMatch() returns true if the condition is met for all elements;
  • min() returns the minimum element using the Comparator as a condition;
  • max() returns the maximum element using the Comparator as a condition;
  • forEach() applies a function to each object (parallel execution order is not guaranteed);
  • forEachOrdered() applies a function to each object, maintaining the order of the elements;
  • toArray() returns an array of values;
  • reduce() allows you to execute aggregate functions and return a single result.

Additionally available for numeric streams:

  • sum() returns the sum of all numbers;
  • average() returns the arithmetic average of all numbers.

Intermediate stream methods

  • filter() filters out records, returning only records that match the condition;
  • skip() allows you to skip a certain number of elements at the beginning;
  • distinct() returns a stream without duplicates (for the equals() method);
  • map() transforms each element;
  • peek() returns the same stream, applying a function to each element;
  • limit() allows you to limit the selection to a certain number of first elements;
  • sorted() allows you to sort the values either in natural order or by specifying a Comparator;
  • mapToInt(), mapToDouble(), mapToLong() - analogs of map() that return a stream of numeric primitives;
  • flatMap(), flatMapToInt(), flatMapToDouble(), flatMapToLong() - similar to map(), but they can create several elements from one element.

For numeric streams, the mapToObj() method is additionally available, which converts a numeric stream back to an object stream.

Examples of usage streams

Display 10 random numbers using forEach()

(new Random())
    .ints()
    .limit(10)
    .forEach(System.out::println);

Display unique squares of numbers using the map() method

Stream
    .of(1, 2, 3, 2, 1)
    .map(s -> s * s)
    .distinct()
    .forEach(System.out::println);

Display the number of empty lines using the filter() method

System.out.println(
    Stream
        .of("Hello", "", ", ", "world", "!")
        .filter(String::isEmpty)
        .count());

Display 10 random numbers in ascending order

(new Random())
    .ints()
    .limit(10)
    .sorted()
    .forEach(System.out::println);

Find the maximum number in a set

Stream
    .of(5, 3, 4, 55, 2)
    .mapToInt(a -> a)
    .max()
    .getAsInt(); // 55

Find the minimum number in a set

Stream
    .of(5, 3, 4, 55, 2)
    .mapToInt(a -> a)
    .min()
    .getAsInt(); // 2

Get the sum of all numbers in a set

Stream
    .of(5, 3, 4, 55, 2)
    .mapToInt()
    .sum(); // 69

Get the average of all numbers

Stream
    .of(5, 3, 4, 55, 2)
    .mapToInt(a -> a)
    .average()
    .getAsDouble(); // 13.8

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