List Interface in Java

The List interface in Java extends the Collection interface and is part of the java.util package. It is used to store ordered collections where duplicates are allowed and elements can be accessed by their index.

• Maintains insertion order
• Allows duplicate elements
• Supports bidirectional traversal using ListIterator

Syntax

List<Type> list = new ArrayList<Type>();

Declaration

public interface List<E> extends Collection<E> { }

Elements of List are:
Java
Python
DSA
C++

Explanation: This Java program demonstrates how to create a List using ArrayList, add elements to it, and iterate through the list to print each element. It uses an enhanced for loop to display all the stored programming languages.

Hierarchy of List Interface

It extends the Collection interface.

The common implementation classes of the List interface are:

• ArrayList: It is implemented using resizable array, offers fast random access but slower insert/delete.
• LinkedList: It is implemented using Doubly-linked list, efficient for frequent insertions and deletions.
• Vector: It is implemented using Legacy synchronized dynamic array, thread-safe but slower.
• Stack: It is implemented using a LIFO (Last-In-First-Out) subclass of Vector for stack operations.

Java List - Operations

List can be used only with a class that implements this interface. Now, let's see how to perform a few frequently used operations on the List.

1. Adding Elements

To add an element to the list, we can use the add()method. This method is overloaded to perform multiple operations based on different parameters. 

• add(Object o): This method is used to add an element at the end of the List.
• add(int index, Object o): This method is used to add an element at a specific index in the List

[Geeks, For, Geeks]

Note: If we try to add element at index 1 before adding elements at index 0 it will throw an error. It is always recommended to add elements in a particular index only when the size is defined or to add them sequentially.

2. Updating Elements

To update an element in a list, use the set() method with the target index and the new value. Since List is indexed, the element is replaced at the specified position.

Initial ArrayList [Geeks, Geeks, Geeks]
Updated ArrayList [Geeks, For, Geeks]

3. Searching Elements 

Searching in a List can be done using indexOf(), lastIndexOf() methods.

• indexOf(Object o): It returns the index of the first occurrence of the specified element in the list or -1 if the element is not found      
• lastIndexOf(Object o): It returns the index of the last occurrence of the specified element in the list or -1 if the element is not found

First Occurrence of 2 is at Index: 1
Last Occurrence of 2 is at Index: 3

4. Removing Elements

To remove an element from a list, we can use the remove() method. This method is overloaded to perform multiple operations based on different parameters.

• remove(Object o): Removes the first occurrence of the specified object from the list.
• remove(int index): Removes the element at the specified index and shifts subsequent elements left.

Initial ArrayList [Geeks, For, Geeks]
After the Index Removal [Geeks, Geeks]
After the Object Removal [Geeks]

5. Accessing Elements

To access an element in the list, we can use the get() method, which returns the element at the specified index.

get(int index): This method returns the element at the specified index in the list.

Geeks
For
Geeks
[Geeks, For, Geeks]

6. Checking if an element is present or not

To check if an element is present in the list, we can use the contains() method. This method returns true if the specified element is present in the list, otherwise, it returns false.

contains(Object o): This method takes a single parameter, the object to be checked if it is present in the list.

Is Geeks present in the list? true

Iterating over List Interface in Java

For larger datasets, Lists can be iterated using:

• Basic for loop with get(index)
• Enhanced for-each loop

These methods allow efficient traversal of elements.

Geeks For Geeks 
Geeks For Geeks 

Complexity of List Interface in Java

Methods of the List Interface

List vs Set

Both the List interface and the Set interface inherits the Collection interface. However, there exists some differences between them.