Stream min() method in Java with Examples

Stream.min() returns the minimum element of the stream based on the provided Comparator. A Comparator is a comparison function, which imposes a total ordering on some collection of objects. min() is a terminal operation which combines stream elements and returns a summary result. So, min() is a special case of reduction. The method returns Optional instance.

Syntax :

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

Where, Optional is a container object which
may or may not contain a non-null value 
and T is the type of objects
that may be compared by this comparator

Exception : This method throws NullPointerException if the minimum element is null.

Example 1 : Minimum from list of Integers.

// Java code for Stream.min() method to get
// the minimum element of the Stream
// according to the provided Comparator.
import java.util.*;

class GFG {

    // Driver code
    public static void main(String[] args)
    {

        // Creating a list of integers
        List<Integer> list = Arrays.asList(-9, -18, 0, 25, 4);

        // Using stream.min() to get minimum
        // element according to provided Integer Comparator
        Integer var = list.stream().min(Integer::compare).get();

        System.out.print(var);
    }
}

Output :

-18

Example 2 : Reverse comparator to get maximum value using min() function.

// Java code for Stream.min() method
// to get the minimum element of the
// Stream according to provided comparator.
import java.util.*;

class GFG {

    // Driver code
    public static void main(String[] args)
    {

        // Creating a list of integers
        List<Integer> list = Arrays.asList(-9, -18, 0, 25, 4);

        // Using Stream.min() with reverse
        // comparator to get maximum element.
        Optional<Integer> var = list.stream()
                    .min(Comparator.reverseOrder());

        // IF var is empty, then output will be Optional.empty
        // else value in var is printed.
        if(var.isPresent()){
        System.out.println(var.get());
        }
        else{
            System.out.println("NULL");
        }

    }
}

Output :

25

Example 3 : Comparing strings based on last characters.

// Java code for Stream.min() method
// to get the minimum element of the
// Stream according to provided comparator.
import java.util.*;

class GFG {

    // Driver code
    public static void main(String[] args)
    {

        // creating an array of strings
        String[] array = { "Geeks", "for", "GeeksforGeeks",
                           "GeeksQuiz" };

        // The Comparator compares the strings
        // based on their last characters and returns
        // the minimum value accordingly.
        Optional<String> MIN = Arrays.stream(array).min((str1, str2) ->
                    Character.compare(str1.charAt(str1.length() - 1),
                                      str2.charAt(str2.length() - 1)));

        // If a value is present,
        // isPresent() will return true
        if (MIN.isPresent())
            System.out.println(MIN.get());
        else
            System.out.println("-1");
    }
}

Output :

for