Streams – max() and min() operations

Stream min() and max() are intermediate operations in Java used to find the min/max value from a Stream of comparable elements. Both methods accept Comparator as an input and return Optional.

You will learn what Optional class is in upcoming tutorials.

Java Stream min() operation

Syntax

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

Example 1:

Get the minimum number from a stream of integers:

class Test {

  public static void main(String[] args) {
    List<Integer> numbers = new ArrayList<>(Arrays.asList(7, 12, 98, 72, 48, 3, 10, 14, 42, 97, 24));

    int minNumber = numbers.stream()
            .min(Comparator.comparing(Integer::valueOf))
            .get();

    System.out.println("Minimum number is: " + minNumber);
  }
}

Output: Minimum number is: 3

The Comparator.comparing() method compares the stream elements based on the input field. In this case, it will compare the integers based on the value of each element.

Example 2:

Get the student with the lowest grade.

Let’s create a Student class first:

class Student {
  private String firstName;
  private String lastName;
  private int grade;

  public Student(String firstName, String lastName, int grade) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.grade = grade;
  }

  public int getGrade() {
    return this.grade;
  }

  @Override
  public String toString() {
    return "student: { firstName: " + firstName + ", lastName: " + lastName + ", grade: " + grade + " }";
  }
}

Now, let’s write the program to return the student with the lowest grade:

class Test {

  public static void main(String[] args) {
    Student student = getStudents().stream()
            .min(Comparator.comparing(Student::getGrade))
            .get();

    System.out.println("Student with the lowest grade: " + student);
  }

  private static List<Student> getStudents() {
    List<Student> students = new ArrayList<>();
    students.add(new Student("Steve", "Rogers", 8));
    students.add(new Student("John", "Doe", 5));
    students.add(new Student("Melissa", "Smith", 7));
    students.add(new Student("Megan", "Norton", 4));
    students.add(new Student("Tom", "Johnson", 9));

    return students;
  }
}

Output: Student with the lowest grade: student: { firstName: Megan, lastName: Norton, grade: 4 }

Note: the get() method returns the value that the Optional is holding.

Java Stream max() operation

Syntax

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

Example 1:

Get the max number from the stream of integers:

class Test {
  public static void main(String[] args) {
    List<Integer> numbers = new ArrayList<>(Arrays.asList(7, 12, 98, 72, 48, 3, 10, 14, 42, 97, 24));

    int maxNumber = numbers.stream()
            .max(Comparator.comparing(Integer::valueOf))
            .get();

    System.out.println("Maximum number is: " + maxNumber);
  }
}

Output: Maximum number is: 98

Example 2:

Get the student with the highest grade.

We will use the same Student class from the above example, and we will write a program that returns the student with the highest grade using the max() method.

class Test {

  public static void main(String[] args) {
    Student student = getStudents().stream()
            .max(Comparator.comparing(Student::getGrade))
            .get();

    System.out.println("Student with the highest grade: " + student);
  }

  private static List<Student> getStudents() {
    List<Student> students = new ArrayList<>();
    students.add(new Student("Steve", "Rogers", 8));
    students.add(new Student("John", "Doe", 5));
    students.add(new Student("Melissa", "Smith", 7));
    students.add(new Student("Megan", "Norton", 4));
    students.add(new Student("Tom", "Johnson", 9));

    return students;
  }
}

Output: Student with the highest grade: student: { firstName: Tom, lastName: Johnson, grade: 9 }

I hope this tutorial was helpful to you. To learn more, check out other Java Functional Programming tutorials.