Java 8 Stream – Find Max and Min from List

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 by key

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());

//Create stream of dates
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);

Program Output.

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

Use above program to find earliest date or latest date from a list of dates.

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);

Program 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);

Program Output.

maxChar = T
minChar = D

Find Min or Max Object by key

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.

Java program to find max or min employee object by it’s age.

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

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

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

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

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

Program Output.

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

Where Employee object is:

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();
	}
}

In this tutorial, we learned to find max value or min value from a stream of primitive values using Java 8 lambda expression. We also learned to find max or min object such as max Date or String.

We also learned to find max object by object property from stream of objects.

Drop me your questions in comments.

Happy Learning !!