Java Stream Max and Min Examples

Learn to find min and max date, number, Char, String or object from stream of comparable elements in easy steps using Comparator.comparing() method.

Table of Contents

Find Min or Max Date
Find Min or Max Number
Find Min or Max Char or String
Find Min or Max Object

Find Min or Max Date

To get max or min date from a stream of dates, you can use Comparator.comparing( LocalDate::toEpochDay ) comparator. toEpochDay() function simply increment count of days for a date where day 0 is for 1970-01-01.

LocalDate start = LocalDate.now();
LocalDate end = LocalDate.now().plusMonths(1).with(TemporalAdjusters.lastDayOfMonth());
List<LocalDate> dates = Stream.iterate(start, date -> date.plusDays(1))
					    .limit(ChronoUnit.DAYS.between(start, end))
					    .collect(Collectors.toList());

// Get Min or Max Date
LocalDate maxDate = dates.stream().max( Comparator.comparing( LocalDate::toEpochDay ) ).get();
LocalDate minDate = dates.stream().min( Comparator.comparing( LocalDate::toEpochDay ) ).get();

System.out.println("maxDate = " + maxDate);
System.out.println("minDate = " + minDate);

Output:

maxDate = 2017-10-30
minDate = 2017-09-13

Find Min or Max Number

To find min and max number from stream of numbers, use Comparator.comparing( Integer::valueOf ) like comparators. Below example is for stream of Integers.

// Get Min or Max Number
Integer maxNumber = Stream.of(1, 2, 3, 4, 5, 6, 7, 8, 9)
					.max(Comparator.comparing(Integer::valueOf)).get();
Integer minNumber = Stream.of(1, 2, 3, 4, 5, 6, 7, 8, 9)
					.min(Comparator.comparing(Integer::valueOf)).get();

System.out.println("maxNumber = " + maxNumber);
System.out.println("minNumber = " + minNumber);

Output:

maxNumber = 9
minNumber = 1

Find Min or Max Char or String

To find min and max string or char from stream of chars, use Comparator.comparing( String::valueOf ) like comparators.

// Get Min or Max String/Char
String maxChar = Stream.of("H", "T", "D", "I", "J").max(Comparator.comparing(String::valueOf)).get();
String minChar = Stream.of("H", "T", "D", "I", "J").min(Comparator.comparing(String::valueOf)).get();

System.out.println("maxChar = " + maxChar);
System.out.println("minChar = " + minChar);

Output:

maxChar = T
minChar = D

Find Min or Max Object

Object comparison involve creating your own custom comparator, first. For example, if I want to get the youngest employee from a stream of Employee objects, then my comparator will look like Comparator.comparing(Employee::getAge). Now use this comparator to get max or min employee object.

List<Employee> emps = new ArrayList<Employee>();

emps.add(new Employee(1, "Lokesh", 36));
emps.add(new Employee(2, "Alex", 46));
emps.add(new Employee(3, "Brian", 52));

Comparator<Employee> comparator = Comparator.comparing(Employee::getAge);

// Get Min or Max Object
Employee minObject = emps.stream().min(comparator).get();
Employee maxObject = emps.stream().max(comparator).get();

System.out.println("minObject = " + minObject);
System.out.println("maxObject = " + maxObject);

Output:

minObject = Id:- 1 Name:- Lokesh Age:- 36
maxObject = Id:- 3 Name:- Brian Age:- 52

Where Employee object is:

Employee.java

class Employee {
	private int id;
	private String name;
	private int age;

	public Employee(int id, String name, int age) {
		super();
		this.id = id;
		this.name = name;
		this.age = age;
	}

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	@Override
	public String toString() {
		StringBuilder str = null;
		str = new StringBuilder();
		str.append("Id:- " + getId() + " Name:- " + getName() + " Age:- " + getAge());
		return str.toString();
	}
}

Drop me your questions relate to these simple techniques to get min and max date, number or objects from java stream.

Happy Learning !!