How do I search a list in Java?

Java Streams (Java 8+) can be used to search for an item within a list by filtering elements based on a condition. The filter() method applies the search criteria, and findAny() returns the first matching element or null if no match is found.

Syntax

Student result = list.stream()
    .filter(s -> s.getRollNo() == rollNo)
    .findAny()
    .orElse(null);

This filters the list for a student with the matching roll number. findAny() returns an Optional, and orElse(null) returns null if no match is found.

Example

The following example searches for students by roll number in a list ?

import java.util.ArrayList;
import java.util.List;

class Student {
    private int rollNo;
    private String name;

    public Student(int rollNo, String name) {
        this.rollNo = rollNo;
        this.name = name;
    }
    public int getRollNo() { return rollNo; }
    public String getName() { return name; }

    @Override
    public String toString() {
        return "[" + this.rollNo + "," + this.name + "]";
    }
}

public class CollectionsDemo {
    public static void main(String[] args) {
        List<Student> list = new ArrayList<>();
        list.add(new Student(1, "Zara"));
        list.add(new Student(2, "Mahnaz"));
        list.add(new Student(3, "Ayan"));
        System.out.println("List: " + list);

        // Search for roll number 3 (exists)
        final int rollNo1 = 3;
        Student found = list.stream()
            .filter(s -> s.getRollNo() == rollNo1)
            .findAny()
            .orElse(null);
        System.out.println("Search rollNo 3: " + found);

        // Search for roll number 4 (does not exist)
        final int rollNo2 = 4;
        Student notFound = list.stream()
            .filter(s -> s.getRollNo() == rollNo2)
            .findAny()
            .orElse(null);
        System.out.println("Search rollNo 4: " + notFound);
    }
}

The output of the above code is ?

List: [[1,Zara], [2,Mahnaz], [3,Ayan]]
Search rollNo 3: [3,Ayan]
Search rollNo 4: null

Roll number 3 returns the matching Student object, while roll number 4 returns null since no match exists in the list.

Conclusion

Use stream().filter().findAny().orElse(null) to search for an item in a Java list by any criteria. For finding all matches instead of just the first one, replace findAny() with collect(Collectors.toList()) to get a list of all matching elements.