Unlocking the Power of ArrayList: Understanding the contains() Method

Syntax and Parameters

The contains() method is a part of the ArrayList class, and its syntax is straightforward:

arraylist.contains(obj)

Here, arraylist is an object of the ArrayList class, and obj is the element you want to check for presence in the list. The method takes a single parameter, obj, which can be of any data type, including integers, strings, and more.

Return Values

The contains() method returns:

• true if the specified element obj is present in the ArrayList
• false if the specified element obj is not present in the ArrayList

Real-World Examples

Let’s dive into some practical examples to illustrate how the contains() method works.

Example 1: Integer ArrayList

Suppose we have an Integer ArrayList named numbers containing the values [1, 2, 3, 4, 5]. We can use the contains() method to check if the number 3 is present in the list:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
System.out.println(numbers.contains(3)); // returns true
System.out.println(numbers.contains(10)); // returns false

Example 2: String ArrayList

Now, let’s consider a String ArrayList named languages containing the values ["Java", "Python", "JavaScript"]. We can use the contains() method to check if the language “Java” is present in the list:

List<String> languages = Arrays.asList("Java", "Python", "JavaScript");
System.out.println(languages.contains("Java")); // returns true
System.out.println(languages.contains("C++")); // returns false

Important Note

The contains() method internally uses the equals() method to find the element. This means that if the specified element matches with an element in the ArrayList, the method returns true. Keep this in mind when working with custom objects and overriding the equals() method.

By mastering the contains() method, you’ll be able to efficiently search and manipulate your ArrayLists, making your Java programming more efficient and effective.