Lists – Array List and Linked List

In this section we will be discussing about the two kinds of lists that would be helpful in storing and manipulating the elements.

This list contains various methods that perform many actions such as, insert, update, delete, and search upon the elements.

Array List –

Arrays list refers to an array kind that helps in working with a bunch of elements. When compared to general arrays that have a fixed size, it offers a huge advantage in terms of its dynamic.

It is provided under the java.util package. It is easier to handle and work with as compared to an array.

Some points about the Array List that we must take note of:

• It can store duplicate elements.
• The insertion order is maintained internally.
• It can access random elements on the basis of the index values.
• It is non- synchronized.
• Implements the List interface.
• It inherits the Abstract List.

Syntax to Declare the ArrayList

ArrayList<String> arayElements = new ArrayList<>();

Manipulations that can be performed using ArrayList

As we said that these lists could help us in performing various kinds of operations on elements. Let’s have a look at some of these operations that could be performed on the Array List.

1. Adding Elements

With the Array List we can add elements to a new or an existing Array List. We is used to add() method to perform the addition operation. It provides the following methods:

• add(Object) – It adds the element at the end of the List
• add(int index, Object) – It adds the element at the particular index in the List.

Example-

import java.util.ArrayList;

public class Test {

	public static void main(String args[]) {
		ArrayList<String> arayElements = new ArrayList<>();

		arayElements.add("QA");
		arayElements.add("TechHub");

		System.out.println("Before adding new element" + arayElements);

		arayElements.add(0, "Welcome");

		System.out.println("After adding new element" + arayElements);
	}
}

Output-

Before adding new element[QA, TechHub]
After adding new element[Welcome, QA, TechHub]

2. Removing Elements

We can remove the elements from the Array List, by using remove() method. It provides the following methods :

• remove(Object) – It removes the element from the ArrayList. If there are similar kinds of elements, then the first occurrence of that object is deleted.
• remove(int index) – It takes the index value as the input, and whichever element is placed at that location is removed from the ArrayList.

Example-

import java.util.ArrayList;

public class Test {

	public static void main(String args[]) {
		ArrayList<String> arayElements = new ArrayList<>();

		arayElements.add("QA");
		arayElements.add("TechHub");
		arayElements.add(0, "Welcome");
		System.out.println("Before removing any element" + arayElements);

		arayElements.remove("Welcome");

		System.out.println("After removing element" + arayElements);
	}
}

Output-

Before removing any element[Welcome, QA, TechHub]
After removing element[QA, TechHub]

3. Update Elements

Once we have added the elements to the Array List, we may want to update the elements. We can do the same by using the set () method.

 Following is the method provided for it:

• set(int index, Object) – It takes the index value as the input which needs to be updated with the new element

Example-

import java.util.ArrayList;

public class Test {

	public static void main(String args[]) {
		ArrayList<String> arayElements = new ArrayList<>();

		arayElements.add("QA");
		arayElements.add("TechHub");
		arayElements.add(0, "Welcome");
		System.out.println("Before Updating any element" + arayElements);

		arayElements.set(0, "Learn From");

		System.out.println("After updating element" + arayElements);
	}
}

Output-

Before removing any element[Welcome, QA, TechHub]
After removing element[Learn From, QA, TechHub]

Some of the additional methods provided for the Array List Manipulation are:

Linked List –

Linked List uses the concept of a doubly linked list. In an ArrayList we were able to work from one end only, but in a LinkedList we can perform manipulations from both the ends, i.e., the starting and the ending of the list.

It is provided under the java.util package. It is easier to handle and work with as compared to an ArrayList.

Some points about the Linked List, that we must take note of:

• Uses Doubly linked list.
• All the elements maintain the insertion order.
• It can contain the duplicate elements.
• It is non-synchronized.
• Manipulations can be performed in a much faster way.

Syntax of Linked List

LinkedList<String> listofElements=new LinkedList<String>();

Manipulation that could be performed using LinkedList

Using the linked list, we can perform a lot of operations, some of which are discussed below:

1. Adding Elements

With the Linked List we can add elements to a new or an existing Linked List. We is used to add() method to perform the add operation. It provides following methods:

• add(Object) – It adds the element at the end of the List
• add(int index, Object) – It adds the element at the particular index in the List.

Example-

import java.util.LinkedList;

public class Test {

	public static void main(String args[]) {
		LinkedList<String> arayElements = new LinkedList<>();

		arayElements.add("QA");
		arayElements.add("TechHub");

		System.out.println("Before adding new element" + arayElements);

		arayElements.add(0, "Welcome");

		System.out.println("After adding new element" + arayElements);
	}
}

Output-

Before adding new element[QA, TechHub]
After adding new element[Welcome, QA, TechHub]

2. Removing Elements

We can remove the elements from the Linked List, by using remove() method. It provides the following methods :

• remove(Object) – It removes the element from the LinkedList. If there are similar kinds of elements, then the first occurrence of that object is deleted.
• remove(int index) – It takes the index value as the input, and whichever element is placed at that location is removed from the Linked List.

Example-

import java.util.LinkedList;

public class Test {

	public static void main(String args[]) {
		LinkedList<String> arayElements = new LinkedList<>();

		arayElements.add("QA");
		arayElements.add("TechHub");
		arayElements.add(0, "Welcome");
		System.out.println("Before removing any element" + arayElements);

		arayElements.remove("Welcome");

		System.out.println("After removing element" + arayElements);
	}
}

Output-

Before removing any element[Welcome, QA, TechHub]
After removing element[QA, TechHub]

3. Update Elements

Once we have added the elements to the Linked List, we may want to update the elements. We can do the same by using the set () method.

 Following is the method provided for it:

• set(int index, Object) – It takes the index value as the input which needs to be updated with the new element

Example-

import java.util.LinkedList;

public class Test {

	public static void main(String args[]) {
		LinkedList<String> arayElements = new LinkedList<>();

		arayElements.add("QA");
		arayElements.add("TechHub");
		arayElements.add(0, "Welcome");
		System.out.println("Before Updating any element" + arayElements);

		arayElements.set(0, "Learn From");

		System.out.println("After updating element" + arayElements);
	}
}

Output-

Before removing any element[Welcome, QA, TechHub]
After removing element[Learn From, QA, TechHub]

Some of the additional methods provided for the Linked List Manipulations are:

Differences between ArrayList & LinkedList