Java Stream findFirst()
May 15, 2020
findFirst method of Stream finds the first element as Optional in this stream. If stream has no element, findFirst returns empty Optional. If the stream has no encounter order then findFirst may select any element. If the selected element by findFirst is null, it throws NullPointerException.
Find the
findFirst declaration from Java doc.
Optional<T> findFirst()
findFirst method returns Optional containing first element in the stream.
The
findFirst throws NullPointerException if selects null value.
The
findFirst is a short-circuiting terminal operation. Stream operations are the group of intermediate and terminal operation. An intermediate operation is a short-circuiting if it may produce a finite stream for infinite input.
Now let us discuss the
findFirst examples.
Example-1: Suppose we have a stream of some integers and we are calling
findFirst method on it.
Stream.of(50, 60, 70).findFirst()
.ifPresent(s -> System.out.println(s));
Find more code.
FindFirstDemo1.java
package com.concretepage;
import java.util.Arrays;
import java.util.List;
public class FindFirstDemo1 {
public static void main(String[] args) {
List<String> list = Arrays.asList("Vijay", "Suresh", "Vinod");
String output = list.stream()
.filter(e -> e.startsWith("V")) // Vijay, Vinod
.findFirst() //Vijay
.orElse("NA");
System.out.println(output);
List<Integer> numList = Arrays.asList(31, 32, 33, 34);
numList.stream()
.filter(n -> n % 2 == 0) // 32, 34
.findFirst() //32
.ifPresent(e -> System.out.println(e));
}
}
Vijay 32
Example-2: Find the example of
findFirst method using IntStream, LongStream and DoubleStream.
FindFirstDemo2.java
package com.concretepage;
import java.util.stream.DoubleStream;
import java.util.stream.IntStream;
import java.util.stream.LongStream;
public class FindFirstDemo2 {
public static void main(String[] args) {
IntStream intStream = IntStream.of(10, 20, 30, 40);
intStream.filter(i -> i > 20).findFirst()
.ifPresent(i -> System.out.println(i));
LongStream longStream = LongStream.of(100, 200, 300);
longStream.filter(l -> l < 250).findFirst()
.ifPresent(l -> System.out.println(l));
DoubleStream doubleStream = DoubleStream.of(100.52, 200.55, 300.66);
doubleStream.filter(d -> d > 200).findFirst()
.ifPresent(l -> System.out.println(l));
}
}
30 100 200.55
Example-3: Find the
findFirst example with parallel stream.
FindFirstDemo3.java
package com.concretepage;
import java.util.ArrayList;
import java.util.List;
public class FindFirstDemo3 {
public static void main(String[] args) {
List<Employee> list = new ArrayList<>();
list.add(new Employee("Emp A", 3000));
list.add(new Employee("Emp B", 4000));
list.add(new Employee("Emp C", 5000));
list.add(new Employee("Emp D", 6000));
list.parallelStream()
.filter(e -> e.getSal() >= 4000 && e.getSal() <= 5000)
.mapToInt(e -> e.getSal())
.findFirst()
.ifPresent(s -> System.out.println(s));
}
}
class Employee {
private String name;
private int sal;
public Employee(String name, int sal) {
this.name = name;
this.sal = sal;
}
//Sets and Gets
}
4000
Example-4: Find the
findFirst example with null value.
FindFirstDemo4.java
package com.concretepage;
import java.util.stream.Stream;
public class FindFirstDemo4 {
public static void main(String[] args) {
Stream.of(null, "A").
findFirst().ifPresent(s -> System.out.println(s));
}
}
NullPointerException.
