ArrayList contains() Method in Java

ArrayList contains() method checks if the list has the specified element or not. Technically, it returns true only when the list contains at least one element where the following condition is met. (o == null ?  e== null : e.equals(o)), where e is each element in the list. You can also check the presence of the null element and custom object in the list.

Syntax:

public boolean contains(Object obj)

Parameter – obj is the element whose presence needs to be checked.
Returns – true if the ArrayList has the specified element; otherwise, it returns false.

ArrayList contains() Example

Let’s look at the program with an Integer type.

import java.util.ArrayList;

public class Demo1 {

	public static void main(String[] args) {
		ArrayList<Integer> numbers = new ArrayList<>();
		numbers.add(12);
		numbers.add(43);
		numbers.add(54);
		numbers.add(23);
		numbers.add(89);
		numbers.add(76);

		System.out.println("ArrayList elements : " + numbers);
		System.out.println("Does the list have 54 : " + numbers.contains(54));
		System.out.println("Does the list have 45 : " + numbers.contains(45));
	}
}

Output:

ArrayList elements : [12, 43, 54, 23, 89, 76]
Does the list have 54 : true
Does the list have 45 : false

contains() with String type

Let’s look at the program to see contains(Element e) with String element type. The time complexity of this method is O(n) where n is the number of elements in the list.

import java.util.ArrayList;

public class ArrayListStringDemo {

	public static void main(String[] args) {
		ArrayList<String> phases = new ArrayList<>();
		phases.add("Coding");
		phases.add("Testing");
		phases.add("Deploying");
		phases.add("Support");

		System.out.println("ArrayList element: " + phases);
		System.out.println("Does the list have Testing: " + phases.contains("Testing"));
		System.out.println("Does the list have Maintainance: " + phases.contains("Maintenance"));
	}
}

Output:

ArrayList element: [Coding, Testing, Deploying, Support]
Does the list have Testing: true
Does the list have Maintainance: false

Using contains with custom object

This program demonstrates how to check the ArrayList contains the custom object.  It checks the presence by calling equals() method of our object.

class Employee {
	private int id;
	private String name;

	public Employee() {
	}

	public Employee(int id, String name) {
		super();
		this.id = id;
		this.name = name;
	}

	@Override
	public String toString() {
		return "Employee [employeeId=" + id + ", employeeName=" + name + "]";
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + id;
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Employee other = (Employee) obj;
		if (id != other.id)
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		return true;
	}
}

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

public class ArrayListDemo {
	public static void main(String[] args) {

		List<Employee> employees = new ArrayList<>();
		employees.add(new Employee(1, "John"));
		employees.add(new Employee(2, "Stevan"));
		employees.add(new Employee(3, "Thomas"));
		employees.add(new Employee(4, "Brian"));

		Employee employeeToCheck = new Employee(3, "Thomas");

		if(employees.contains(employeeToCheck)) {
			System.out.println("Brian is present in employees.");
		} else {
			System.out.println("Brian is not present in employees.");
		}

	}
}

That’s all about the contains method. You can also go through our articles where we explain how to find the indexOf() and lastIndexOf() the element. Please share this article if you liked it.

Further References:

ArrayList Documentation