Java stream findFirst() explanation with example

Java stream findFirst() explanation with example:

findFirst() is used to find the first element in a stream in Java. It returns one Optional value holding the element found. If the stream is empty, it will return one empty optional. In this post, I will show you how findFirst() works with an example.

Definition of findFirst:

findFirst is defined as below:

Optional<T> findFirst()

It returns an optional value holding the element from the stream.
It returns one empty optional if the stream is empty.
It returns NullPointerException if the selected element is null.

Example of findFirst:

Let’s consider the below example program:

package com.company;

import java.util.Arrays;
import java.util.Optional;
import java.util.stream.Stream;

public class Main {
    public static void main(String[] args){
       Stream<Integer> intStream = Arrays.asList(10, 20, 30, 40, 50, 40).stream();

       Optional firstValue = intStream.findFirst();

       System.out.println(firstValue);
    }
}

It will print Optional(10).

We can also check if a value exists or not using isPresent() and get the value using get():

package com.company;

import java.util.Arrays;
import java.util.Optional;
import java.util.stream.Stream;

public class Main {
    public static void main(String[] args){
       Stream<Integer> intStream = Arrays.asList(10, 20, 30, 40, 50, 40).stream();

       Optional firstValue = intStream.findFirst();

       if(firstValue.isPresent()){
           System.out.println(firstValue.get());
       }
    }
}

It will print 10.

Example of using filter with findFirst:

We can also use filter with findFirst. filter can filter out a value in the stream and if we use findFirst with filter, we can get the first value that matches the filter condition.

For example:

package com.company;

import java.util.Arrays;
import java.util.Optional;
import java.util.stream.Stream;

public class Main {
    public static void main(String[] args){
       Stream<Integer> intStream = Arrays.asList(1, 4, 6, 7, 3, 9, 10).stream();

       Optional firstValue = intStream.filter(x -> x%2 == 0).findFirst();

       if(firstValue.isPresent()){
           System.out.println(firstValue.get());
       }
    }
}

Here, we are using filter and findFirst to find the first even number in the number list. It will print 4 as the output.

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Java stream findFirst() explanation with example