ArrayList
ArrayList is like a array which size will be grown dynamically. Some of the main features of arraylist are given below
- Arraylist allows duplicates.
- It allows null, also it will allow multiple null.
- It’ s not threadsafe which means it is not synchronized.
- Arraylist will maintain insertion order
- It will not be sorted. (since it maintain insertion order it will not be sorted.) But we can sort the arrralylist using Collections.sort(). We will see arraylist sorting in a more detailed manner soon.
- It can be traverse using
- For each
- Iterators
- Indexes
Note: Collections will not allow primitives. So when primitive is added to a collection, it get automatically converted into its equivalent Wrapper Class and loaded as an object into the collection.
package ArrayList;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
public class ArrayListImplementation {
public static void main(String[] args) {
// TODO Auto-generated method stub
List integerList = new ArrayList();
//Adding an Object, int will be automatically
//converted to Wrapper class
integerList.add(1);
integerList.add(2);
integerList.add(34);
integerList.add(4);
integerList.add(3);
System.out.println("Values in integerList "+integerList);
integerList.add(3, 98);
System.out.println("Values in integerList after adding"
+ " in a specified (3rd) position"+integerList);
/* addAll -> will add a collection
of List objects to another list */
List integerListTwo = new ArrayList();
integerListTwo.add(65);
integerListTwo.add(73);
integerList.addAll(integerListTwo);
System.out.println("Values in integerListTwo " +integerListTwo);
System.out.println("Values in integerList after adding"
+ " in a Collection (another list)"+integerList);
/*addAll -> will also a collection of List objects
to another list at a specified position*/
integerList.addAll(6, integerListTwo);
System.out.println("Values in integerListTwo after adding"
+ " in a specified (6th) position of integerList "+integerList);
//contains -> Returns true if this list contains the specified element.
System.out.println("Check integerList contains 5 or not :"+integerList.contains(5));
//containsAll -> Returns true if this list contains the specified collection (integerListTwo).
System.out.println("Check integerList contains integerListTwo "
+ "collection or not :"+integerList.containsAll(integerListTwo));
//equals
System.out.println(integerList.equals(integerListTwo));
System.out.println(integerList.equals(integerList));
//get -> Returns the element at the specified position in this list
System.out.println("Get the element at the specified positon "+ integerList.get(8));
//indexOf -> Returns the index of the first occurrence of the specified
//element in this list, or -1 if this list does not contain the element.
System.out.println("Index of 73 is at "+integerList.indexOf(73));
//Iterator -> Returns an iterator over the elements in this list in proper sequence.
System.out.println("Elements in iterator");
System.out.println("--------------------");
Iterator iterator=integerList.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
//lastIndexOf -> Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element
System.out.println("lastIndexOf of 3 is :"+integerList.lastIndexOf(3));
//set -> Replaces the element at the specified position in this list with the specified element (optional operation).
integerList.set(0, 18);
System.out.println("After setting 18 at 0th position, value of integerLis"+integerList);
//size -> Returns the number of elements in this list. If this list contains more than
//Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
System.out.println("Size of integerList :"+integerList.size());
//remove ->Removes the element at the specified position in this list (optional operation).
//Shifts any subsequent elements to the left (subtracts one from their indices). Returns the element that was removed from the list.
integerList.remove(2);
System.out.println(" remove 34 which is at 2nd position: "+integerList);
//removeAll ->Removes from this list all of its elements that are contained in the specified collection (optional operation).
integerList.removeAll(integerListTwo);
System.out.println("After removing integerListTwo :"+integerList);
integerList.addAll(integerListTwo);
//retainAll -> Retains only the elements in this list that are contained
//in the specified collection (optional operation).In other words, removes from this list all
//of its elements that are not contained in the specified collection.
integerList.retainAll(integerListTwo);
System.out.println("retain all will remove all elements except integgerListTwo :"+integerList);
/*clear ---> Removes all of the elements from this list (optional operation).
The list will be empty after this call returns.*/
integerList.clear();
System.out.println("After clearing the list :"+integerList);
//isEmpty() --> will check whether the list is empty or not
System.out.println("checking the list is empty or not :"+integerList.isEmpty());
}
}
Output is: Values in integerList [1, 2, 34, 4, 3] Values in integerList after adding in a specified (3rd) position[1, 2, 34, 98, 4, 3] Values in integerListTwo [65, 73] Values in integerList after adding in a Collection (another list)[1, 2, 34, 98, 4, 3, 65, 73] Values in integerListTwo after adding in a specified (6th) position of integerList [1, 2, 34, 98, 4, 3, 65, 73, 65, 73] Check integerList contains 5 or not :false Check integerList contains integerListTwo collection or not :true false true Get the element at the specified positon 65 Index of 73 is at 7 Elements in iterator -------------------- 1 2 34 98 4 3 65 73 65 73 lastIndexOf of 3 is :5 After setting 18 at 0th position, value of integerLis[18, 2, 34, 98, 4, 3, 65, 73, 65, 73] Size of integerList :10 remove 34 which is at 2nd position: [18, 2, 98, 4, 3, 65, 73, 65, 73] After removing integerListTwo :[18, 2, 98, 4, 3] retain all will remove all elements except integgerListTwo :[65, 73] After clearing the list :[] checking the list is empty or not :true
package ArrayList;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
public class linkedListImplementation {
public linkedListImplementation() {
// TODO Auto-generated constructor stub
}
public static void main(String[] args) {
// TODO Auto-generated method stub
List integerList = new LinkedList();
//Adding an Object, int will be automatically
//converted to Wrapper class
integerList.add(1);
integerList.add(2);
integerList.add(34);
integerList.add(4);
integerList.add(3);
System.out.println("Values in integerList "+integerList);
integerList.add(3, 98);
System.out.println("Values in integerList after adding"
+ " in a specified (3rd) position"+integerList);
/* addAll -> will add a collection
of List objects to another list */
List integerListTwo = new LinkedList();
integerListTwo.add(65);
integerListTwo.add(73);
integerList.addAll(integerListTwo);
System.out.println("Values in integerListTwo " +integerListTwo);
System.out.println("Values in integerList after adding"
+ " in a Collection (another list)"+integerList);
/*addAll -> will also a collection of List objects
to another list at a specified position*/
integerList.addAll(6, integerListTwo);
System.out.println("Values in integerListTwo after adding"
+ " in a specified (6th) position of integerList "+integerList);
//contains -> Returns true if this list contains the specified element.
System.out.println("Check integerList contains 5 or not :"+integerList.contains(5));
//containsAll -> Returns true if this list contains the specified collection (integerListTwo).
System.out.println("Check integerList contains integerListTwo "
+ "collection or not :"+integerList.containsAll(integerListTwo));
//equals
System.out.println(integerList.equals(integerListTwo));
System.out.println(integerList.equals(integerList));
//get -> Returns the element at the specified position in this list
System.out.println("Get the element at the specified positon "+ integerList.get(8));
//indexOf -> Returns the index of the first occurrence of the specified
//element in this list, or -1 if this list does not contain the element.
System.out.println("Index of 73 is at "+integerList.indexOf(73));
//Iterator -> Returns an iterator over the elements in this list in proper sequence.
System.out.println("Elements in iterator");
System.out.println("--------------------");
Iterator iterator=integerList.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
//lastIndexOf -> Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element
System.out.println("lastIndexOf of 3 is :"+integerList.lastIndexOf(3));
//set -> Replaces the element at the specified position in this list with the specified element (optional operation).
integerList.set(0, 18);
System.out.println("After setting 18 at 0th position, value of integerLis"+integerList);
//size -> Returns the number of elements in this list. If this list contains more than
//Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
System.out.println("Size of integerList :"+integerList.size());
//remove ->Removes the element at the specified position in this list (optional operation).
//Shifts any subsequent elements to the left (subtracts one from their indices). Returns the element that was removed from the list.
integerList.remove(2);
System.out.println(" remove 34 which is at 2nd position: "+integerList);
//removeAll ->Removes from this list all of its elements that are contained in the specified collection (optional operation).
integerList.removeAll(integerListTwo);
System.out.println("After removing integerListTwo :"+integerList);
integerList.addAll(integerListTwo);
//retainAll -> Retains only the elements in this list that are contained
//in the specified collection (optional operation).In other words, removes from this list all
//of its elements that are not contained in the specified collection.
integerList.retainAll(integerListTwo);
System.out.println("retain all will remove all elements except integgerListTwo :"+integerList);
/*clear ---> Removes all of the elements from this list (optional operation).
The list will be empty after this call returns.*/
integerList.clear();
System.out.println("After clearing the list :"+integerList);
//isEmpty() --> will check whether the list is empty or not
System.out.println("checking the list is empty or not :"+integerList.isEmpty());
}
}
Output:
Values in integerList [1, 2, 34, 4, 3]
Values in integerList after adding in a specified (3rd) position[1, 2, 34, 98, 4, 3]
Values in integerListTwo [65, 73]
Values in integerList after adding in a Collection (another list)[1, 2, 34, 98, 4, 3, 65, 73]
Values in integerListTwo after adding in a specified (6th) position of integerList [1, 2, 34, 98, 4, 3, 65, 73, 65, 73]
Check integerList contains 5 or not :false
Check integerList contains integerListTwo collection or not :true
false
true
Get the element at the specified positon 65
Index of 73 is at 7
Elements in iterator
——————–
1
2
34
98
4
3
65
73
65
73
lastIndexOf of 3 is :5
After setting 18 at 0th position, value of integerLis[18, 2, 34, 98, 4, 3, 65, 73, 65, 73]
Size of integerList :10
remove 34 which is at 2nd position: [18, 2, 98, 4, 3, 65, 73, 65, 73]
After removing integerListTwo :[18, 2, 98, 4, 3]
retain all will remove all elements except integgerListTwo :[65, 73]
After clearing the list :[]
checking the list is empty or not :true
Difference between ArrayList and Linked list
| Reason | ArrayList | Linked List |
| Search | Faster because it has index based search. Eg get(index) | Slower.Since it implements doubly linked list which requires traversal through all the elements to search an element. |
| Deletion | Slower | Faster |
| Insertion | Faster | Slower |
Similarities:
• Both implements List interface and extends AbstractList.
• Both will maintain Insertion Order.
• Both are non-synchronized (non threadsafe).
• Both can be made synchronized by using Collections.synchronizedList method
When to use Linked List and When to use arraylist:
1. For insertion and deletion go for linked list.
2. For search go for arraylist.
