Java 8 stream min max comparator examples

Today, i show you about Java 8 stream min max comparator examples which finds min and max date, number, Char, String or object from stream of comparable elements using Comparator.comparing() method. Java 8 introduced several enhancements to the Comparator interface, including a handful of static functions that are of great utility.

Min or Max Number

Now we have a comparator for integer number like this

Comparator.comparing(Integer::valueOf)

1	Comparator.comparing(Integer::valueOf)

Demo program

public class MinMaxNumberDemo {
	public static void main(String[] args) {
		// Find Min or Max Number
		Integer max = Stream.of(-1, -2, -3, 3, 2, 1).max(Comparator.comparing(Integer::valueOf)).get();
		Integer min = Stream.of(-1, -2, -3, 3, 2, 1).min(Comparator.comparing(Integer::valueOf)).get();

		System.out.println("max = " + max);
		System.out.println("min = " + min);
	}
}

public class MinMaxNumberDemo {

public static void main(String[] args) {

// Find Min or Max Number

Integer max = Stream.of(-1, -2, -3, 3, 2, 1).max(Comparator.comparing(Integer::valueOf)).get();

Integer min = Stream.of(-1, -2, -3, 3, 2, 1).min(Comparator.comparing(Integer::valueOf)).get();

System.out.println("max = " + max);

System.out.println("min = " + min);

}

Output

max = 3
min = -3

1 2	max = 3 min = -3

Min or Max String

Now we have a comparator for string like this

	Comparator.comparing(String::valueOf)

1	Comparator.comparing(String::valueOf)

Our demo program

public class MinMaxStringDemo {
	public static void main(String[] args) {
		// Find Min or Max String
		String maxString = Stream.of("A1", "B1", "C1", "D1").max(Comparator.comparing(String::valueOf)).get();
		String minString = Stream.of("A1", "B1", "C1", "D1").min(Comparator.comparing(String::valueOf)).get();

		System.out.println("maxString = " + maxString);
		System.out.println("minString = " + minString);
	}
}

public class MinMaxStringDemo {

public static void main(String[] args) {

// Find Min or Max String

String maxString = Stream.of("A1", "B1", "C1", "D1").max(Comparator.comparing(String::valueOf)).get();

String minString = Stream.of("A1", "B1", "C1", "D1").min(Comparator.comparing(String::valueOf)).get();

System.out.println("maxString = " + maxString);

System.out.println("minString = " + minString);

}

Output

maxString = D1
minString = A1

1 2	maxString = D1 minString = A1

Min or Max Date

Now we have a comparator for string like this

	Comparator.comparing(LocalDate::toEpochDay)

1	Comparator.comparing(LocalDate::toEpochDay)

Demo program

public class MinMaxDateDemo {
	public static void main(String[] args) {
		
		LocalDate currentDate = LocalDate.now();
		LocalDate endDate = LocalDate.now().with(TemporalAdjusters.lastDayOfMonth());
		List<LocalDate> dates = Stream.iterate(currentDate, date -> date.plusDays(1))
		                        .limit(ChronoUnit.DAYS.between(currentDate, endDate))
		                        .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);
	}
}

public class MinMaxDateDemo {

public static void main(String[] args) {

LocalDate currentDate = LocalDate.now();

LocalDate endDate = LocalDate.now().with(TemporalAdjusters.lastDayOfMonth());

List<LocalDate> dates = Stream.iterate(currentDate, date -> date.plusDays(1))

.limit(ChronoUnit.DAYS.between(currentDate, endDate))

.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 = 2017-11-29
minDate = 2017-11-23

1 2	maxDate = 2017-11-29 minDate = 2017-11-23

Min or Max Object

We’re considering the POJO like this

	public class People {
		public int age;
		public String gender;
		public String name;
		
		//getter and setter
	}

public class People {

public int age;

public String gender;

public String name;

//getter and setter

}

And We’re finding the max and min age of people, so our comparator should be such as

Comparator.comparing(People::getAge)

1	Comparator.comparing(People::getAge)

Demo program

public class MinMaxObjectDemo {
	public static void main(String[] args) {
		People a = new People(28, "M", "Mr A");
		People b = new People(25, "M", "Mr B");
		People c = new People(21, "M", "Mr C");
		People d = new People(21, "M", "Mr D");

		Collection<People> list = Arrays.asList(a, b, c, d);

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

		// Find Min or Max age of People object
		People minAge = list.stream().min(comparator).get();
		People maxAge = list.stream().max(comparator).get();

		System.out.println("minAge = " + minAge);
		System.out.println("maxAge = " + maxAge);
	}
}