Java 25 (LTS) reference · List and ArrayList Methods

Java List contains() Method

Return true if the list holds an element equal to the given one (using equals()). O(n) for ArrayList.

Java 25 (LTS) Since Java 1.0

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Syntax

list.contains(object)

Parameters

Parameter	Description
`object` Object	The value to look for.

Return value

true or false.

Examples

Membership check

import java.util.*;

public class Main {
    public static void main(String[] args) {
        List<String> roles = List.of("admin", "editor");
        System.out.println(roles.contains("admin"));
        System.out.println(roles.contains("viewer"));
    }
}

Output

true
false

Run this on your computer — see “Get Started” for setup.

Use a Set for frequent lookups

import java.util.*;

public class Main {
    public static void main(String[] args) {
        List<Integer> big = new ArrayList<>();
        for (int i = 0; i < 100_000; i++) big.add(i);
        Set<Integer> fast = new HashSet<>(big);  // contains() on a HashSet is O(1)
        System.out.println(big.contains(99_999) + " " + fast.contains(99_999));
    }
}