What is arraylist in collection framework?

Answer 1

The java.util.ArrayList class is one of the most commonly used of all the classes in the Collections Framework. Some of the advantages ArrayList has over arrays are

• It can grow dynamically.

• It provides more powerful insertion and search mechanisms than arrays.

Let's take a look at using an ArrayList that contains Strings. A key design goal of the Collections Framework was to provide rich functionality at the level of the main interfaces: List, Set, and Map. In practice, you'll typically want to instantiate an ArrayList polymorphically like this:

List myFirstArrayList = new ArrayList();

As of Java 5 you'll want to say

List myFirstArrayList = new ArrayList();

This kind of declaration follows the object oriented programming principle of "coding to an interface", and it makes use of generics. We'll say lots more about generics in future, but for now just know that, as of Java 5, the syntax is the way that you declare a collection's type. (Prior to Java 5 there was no way to specify the type of a collection, and when we cover generics, we'll talk about the implications of mixing Java 5 (typed) and pre-Java 5 (untyped) collections.)

In many ways, ArrayList is similar to a String[] in that it declares a container that can hold only Strings, but it's more powerful than a String[]. Let's look at some of the capabilities that an ArrayList has

List test = new ArrayList();

String s = "hi";

test.add("string");

test.add(s);

test.add(s+s);

System.out.println(test.size());

System.out.println(test.contains(42));

System.out.println(test.contains("hihi"));

test.remove("hi");

System.out.println(test.size());

which produces

3

false

true

2

There's lots going on in this small program. Notice that when we declared the ArrayList we didn't give it a size. Then we were able to ask the ArrayList for its size, we were able to ask it whether it contained specific objects, we removed an object right out from the middle of it, and then we rechecked its size.