Java - List Interface

List Interface

The List interface extends Collection and declares the behavior of a collection that stores a sequence of elements.

• Elements can be inserted or accessed by their position in the list, using a zero-based index.

• A list may contain duplicate elements.

• In addition to the methods defined by Collection, List defines some of its own, which are summarized in the following table.

• Several of the list methods will throw an UnsupportedOperationException if the collection cannot be modified, and a ClassCastException is generated when one object is incompatible with another.

Declaration of Java List Interface

The following is the declaration of a List interface in Java:

public interface List<E> extends Collection<E>; 

Creating a Java list

A Java list is created using the List interface. The syntax is as follows -

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

Example of List Interface

The following example demonstrates an example of List interface in Java -

import java.util.*;

// The Main class
public class Main {
  public static void main(String[] args) {
    // Creating two lists using List interface
    List < Integer > list1 = new ArrayList < Integer > ();
    List < Integer > list2 = new ArrayList < Integer > ();

    // Adding elements to list 1
    list1.add(0, 10);
    list1.add(1, 20);

    // Printing list 1
    System.out.println("list1 : " + list1);

    // Adding elements to list 2
    list2.add(10);
    list2.add(20);
    list2.add(30);

    // Adding all elements of list 2 in list 1
    list1.addAll(1, list2);

    // Printing list 2
    System.out.println("list2 : " + list2);

    // Removes an element from list 1 (from index 1)
    list1.remove(1);

    // Printing list 1
    System.out.println("list1 after removing an element: " + list1);

    // get() method
    System.out.println("list1 using get() : " + list1.get(2));

    // Replacing element
    list1.set(0, 50);

    // Printing the list 1
    System.out.println("list1 : " + list1);
  }
}

Output

list1 : [10, 20]
list2 : [10, 20, 30]
list1 after removing an element: [10, 20, 30, 20]
list1 using get() : 30
list1 : [50, 20, 30, 20]

List Interface Methods

The following are the methods of List Interface in Java -

More Examples of List Interface

Example: Java List using ArrayList

The above interface has been implemented using ArrayList. Following is the example to explain few methods from various class implementation of the above collection methods −

import java.util.ArrayList;
import java.util.List;
public class CollectionsDemo {

   public static void main(String[] args) {
      List<String> a1 = new ArrayList<>();
      a1.add("Zara");
      a1.add("Mahnaz");
      a1.add("Ayan");      
      System.out.println(" ArrayList Elements");
      System.out.print("\t" + a1);
   }
}

Output

 ArrayList Elements
   [Zara, Mahnaz, Ayan]

Example: Java List using LinkedList

The above interface has been implemented using LinkedList. Following is the example to explain few methods from various class implementation of the above collection methods −

import java.util.LinkedList;
import java.util.List;
public class CollectionsDemo {

   public static void main(String[] args) {
      List<String> a1 = new LinkedList<>();
      a1.add("Zara");
      a1.add("Mahnaz");
      a1.add("Ayan");      
      System.out.println(" LinkedList Elements");
      System.out.print("\t" + a1);
   }
}

Output

 LinkedList Elements
   [Zara, Mahnaz, Ayan]

Example: Adding Element to Java List

The above interface has been implemented using ArrayList. Following is another example to explain few methods from various class implementation of the above collection methods −

import java.util.ArrayList;
import java.util.List;
public class CollectionsDemo {

   public static void main(String[] args) {
      List<String> a1 = new ArrayList<>();
      a1.add("Zara");
      a1.add("Mahnaz");
      a1.add("Ayan");      
      System.out.println(" ArrayList Elements");
      System.out.print("\t" + a1);
      
      // remove second element
      a1.remove(1);
      
      System.out.println("\n ArrayList Elements");
      System.out.print("\t" + a1);
   }
}

Output

 ArrayList Elements
   [Zara, Mahnaz, Ayan]
 ArrayList Elements
   [Zara, Ayan]