Filter and find an element from List using Java Stream API

Using Stream API filter and findFirst() methods
Using Stream API filter and findAny() methods

Please note that in below examples, in order to get a Stream Object from List, you can also use List#parallelStream() method, but use it only if the List implementation supports thread-safety and parallelism (for example CopyOnWriteArrayList).

From Java 8 onwards, you can use Java Stream API to filter elements from a Collection like List, and in this approach we are going use findFirst() method on Stream which returns the first occurrence of that element.

In order to follow below example, create a class called Person and declare two variables, name as String and age as integer.

public class Person { private String name; private int age; public Person(String name, int age) { this.name = name; this.age = age; } public String getName() { return name; } public int getAge() { return age; } @Override public String toString() { return "[name : " +name + " , age : "+age +"]"; } }

Let's write a program to find the first person from list whose age is greater than 30.

public static void findFirstMatch() { List<Person> persons = List.of( new Person("Person A", 29), new Person("Person B", 32), new Person("Person C", 45), new Person("Person D", 39) ); Optional<Person> firstMatch = persons.stream(). filter(person -> person.getAge() >30).findFirst(); if(firstMatch.isPresent()) { System.out.println("Person with match found : " + firstMatch.get()); } else { System.out.println("No match found"); } }

Explanation of above code:

First we called stream() method on List<Person> that returns a Stream<Person> objects.
Then on the Stream object, we called filter() method with a predicate person.getAge() >30. This essentially pass every Person object from the list and check whether predicate condition is passed.
Then we are calling findFirst() , when the first match of predicate condition occurred on a Person object, then it returns and exits there. This method returns Optional<Person>.
Optional is kind of a container class which holds an Object with some utility methods, you can check isPresent() method on Optional, if it present you can retrieve the underlying object using get() on Optional. See this article to know more on Optional.

When you run the above program, you will get the below output.

Person with match found : [name : Person B , age : 32]

This approach is same as above except that in place of findFirst(), we are going call findAny() and the main difference is that the behavior of this operation is explicitly non deterministic; it is free to select any element in the stream. This is to allow for maximal performance in parallel operations; the cost is that multiple invocations on the same source may not return the same result. (If a stable result is desired, use findFirst() instead.)

public static void findFirstMatch() { List<Person> persons = List.of( new Person("Person A", 29), new Person("Person B", 32), new Person("Person C", 45), new Person("Person D", 39) ); Optional<Person> firstMatch = persons.stream(). filter(person -> person.getAge() >30).findAny(); if(firstMatch.isPresent()) { System.out.println("Person with match found : " + firstMatch.get()); } else { System.out.println("No match found"); } }

When you run the above program, you will get the below output. Please note that the output may not be same in your case and may vary.

Person with match found : [name : Person B , age : 32]

Above example complete source code can be found here on Github

Explanation of above code:

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