[Java] How to operate List using Stream API

What is Stream API?

The Stream API is a feature introduced in Java8. It is for handling aggregates such as arrays and collections. It is a convenient API that can aggregate values ​​and process using data. By using Stream, the extended for statement can be simplified.

How to use Stream

Count the number of each element (count)

public class Sample {
	public static void main(String[] args) {

		List<String> JS = new ArrayList<>(Arrays.asList("Vue", "React", "Angular"));

		long count = JS.stream().count();
		System.out.println(count); // 3
	}
}

Judge and extract each element by condition (filter)

The following is the process to remove "Angular" and display the list.

public class Sample {
	public static void main(String[] args) {

		List<String> JS = new ArrayList<>(Arrays.asList("Vue", "React", "Angular"));

        JS.stream()
        .filter(s -> !s.equals("Angular"))
        .forEach(System.out::println); // Vue React
	}
}

Sorted elements

The second sorted method is in descending order because the reverseOrder method of the Comparator interface is specified as an argument.

public class Sample {
	public static void main(String[] args) {

	    List<String> JS = new ArrayList<>(Arrays.asList("Vue", "React", "Angular"));

		JS.stream()
			.sorted() //Ascending order because no arguments are passed
			.forEach(System.out::println); // Angular React Vue

		JS.stream()
			.sorted(Comparator.reverseOrder()) //In descending order
			.forEach(System.out::println); // Vue React Angular
	}
}

Do all element conditions match (allMatch)

The allMatch method returns true if they all match.

public class Sample {
	public static void main(String[] args) {

		List<Integer> num1 = new ArrayList<>(Arrays.asList(10,38,3));

        boolean a = num1.stream()
        		.allMatch(b -> b > 10); //Are all elements greater than 10
        System.out.println(a); //false

        boolean c = num1.stream()
        		.allMatch(d -> d > 1); //Are all elements greater than 1
        System.out.println(c); //true
	}
}

Does any of the element's conditions match (anyMatch)?

The anyMatch method returns true if at least one matches.

public class Sample {
	public static void main(String[] args) {

		List<Integer> num1 = new ArrayList<>(Arrays.asList(10,38,3));

        boolean a = num1.stream()
        		.anyMatch(b -> b > 40); //Are there any elements greater than 40?
        System.out.println(a); //false

        boolean c = num1.stream()
        		.anyMatch(d -> d > 30); //Are there any elements greater than 30
        System.out.println(c); //true
	}
}

Is there any element that matches the condition (noneMatch)?

The noneMatch method returns true if there are no matches.

public class Sample {
	public static void main(String[] args) {

		List<Integer> num1 = new ArrayList<>(Arrays.asList(10,38,3));

        boolean a = num1.stream()
        		.noneMatch(b -> b > 7); //Is there any element larger than 7?
        System.out.println(a); //false

        boolean c = num1.stream()
        		.noneMatch(d -> d > 40); //Is there any element larger than 40?
        System.out.println(c); //true
	}
}

reference

Interface Stream Java8 StreamAPI