arraylist search for value o(1) without hashset code example

Example 1: Fast Lookup of Java

Set<String> animals = new HashSet<String>(
                          Arrays.asList("cat", "dog", "squirrel", "raccoon"));
if (animals.contains("dog")) {
    System.out.println("Yep, dog's here!"); // prints
}
if (!animals.contains("aardvark")) {
    System.out.println("Ah, aardvark's missing!"); // prints
}

Example 2: java check if key exists in list

if (lista.contains(conta1)) {
    System.out.println("Account found");
} else {
    System.out.println("Account not found");
}