ArrayList
Published Oct 28, 2021Updated Mar 21, 2022
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The ArrayList
class uses dynamic arrays that are resizable, unlike traditional fixed arrays. However, each element must still be of the same type. Elements can be added or removed at any time, making the ArrayList
more flexible.
Some other important points about the ArrayList
class include:
- It has the ability to contain duplicate elements.
- It maintains insertion order.
- It is non-synchronized and, therefore, not safe for multiple threading.
- It allows random access since arrays work on an index basis.
- The space/time complexity is a bit slower than a LinkedList due to the nature of adding/removing elements.
Syntax
This class is imported with the java.util
package.
import java.util.ArrayList;
The syntax for defining an instance of ArrayList
is similar to defining a traditional array. A key difference is that angle brackets <>
are used instead of square brackets:
ArrayList<DataType> arrayListInstance = new ArrayList<DataType>();
Example
In the example below, a new ArrayList
instance arr
is defined. There are print statements throughout to show elements being added to and removed from arr
before it is ultimately cleared:
// Import from the java.util packageimport java.util.ArrayList;public class Example {public static void main(String []args) {ArrayList<String> arr = new ArrayList<>();System.out.println(arr); // Currently emptyarr.add("hello");arr.add("India");System.out.println(arr);arr.remove("hello");System.out.println(arr.size()); // Prints size of ArrayListarr.clear();System.out.println(arr); // Empty again}}
The output would be:
[][hello, India]1[]
ArrayList
- .add()
- Adds an element to an ArrayList.
- .addAll()
- Adds a collection to an ArrayList.
- .get()
- Retrieves the element present in a specified position in an ArrayList.
- .indexOf()
- Returns the index of the first occurrence of a given element, or -1 if not found.
- .remove()
- Removes a specified element from an ArrayList.
- .set()
- Replaces the element present in a specified position in an ArrayList.
- .size()
- Returns the number of elements in the ArrayList.
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