Java Stream max()

The Stream max() method is used to select the largest element in the Stream according to the Comparator used for comparing the elements.

The Comparator imposes a total ordering on the Stream elements which may not have a natural ordering.

1. Stream max() Method

1.1. Method Syntax

• The method takes a non-interfering and stateless Comparator to compare elements of the stream.
• It returns an Optional describing the maximum element of the stream, or an empty Optional if the stream is empty.
• The max() method throws NullPointerException if the maximum element found is null.

Optional<T> max(Comparator<? super T> comparator)

1.2. Description

• The max() method is a terminal operation. So the Stream cannot be used after this method has been executed.
• It returns the maximum/largest element of this stream according to the provided Comparator.
• This is a special case of a stream reduction.
• The method argument shall be a non-interfering, stateless Comparator.
• The method returns an Optional describing the maximum element of this stream, or an empty Optional if the stream is empty.
• It may throw NullPointerException if the maximum element is null.

2. Java Stream max() Example

Example 1: Largest element in the Stream with Lambda Expression

Java example to find the largest number from a stream of numbers using comparator as lambda expression.

List<Integer> list = Arrays.asList(2, 4, 1, 3, 7, 5, 9, 6, 8);

Optional<Integer> maxNumber = list.stream()
      .max((i, j) -> i.compareTo(j));

System.out.println(maxNumber.get());

Program output.

9

Example 2: Largest element in the Stream with Comparator

Java example to find the largest number from a stream of numbers using custom comparator.

List<Integer> list = Arrays.asList(2, 4, 1, 3, 7, 5, 9, 6, 8);
 
Comparator<Integer> maxComparator = new Comparator<Integer>() {
   
  @Override
  public int compare(Integer n1, Integer n2) {
    return n1.compareTo(n2);
  }
};

Optional<Integer> maxNumber = list.stream()
      .max(maxComparator);

System.out.println(maxNumber.get());

Program output.

9

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