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- ArrayList is a class that implements the List interface.
- The advantage of ArrayList over the general Array is that ArrayList is dynamic and the size of ArrayList can grow or shrink.
- ArrayList stores the elements in the insertion order.
- ArrayList can have duplicate elements. ArrayList is non synchronized.
Creating an ArrayList:
Syntax:
| ArrayList obj = new ArrayList(); //Without Generics
ArrayList<DataType> obj = new ArrayList<Data Type>(); //Using Generics |
Example:
ArrayList<String> name = new ArrayList<String>();
Adding elements in the ArrayList:
Elements can be added to an arraylist object by using add() method of the ArrayList class.
Syntax:
| add(E e) |
To Add an element at a specific index.
Syntax:
| add(int index, Element e) |
Example:
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public class ArrayListExample{ public static void main(String[] args) { ArrayList<String> al = new ArrayList<String>(); al.add("Anjali"); al.add("Bala"); al.add(1,"Anu"); //adding “Anu” in the index 1 al.add("Anu"); for(String s:al){ //iterating using for loop System.out.println("Name:"+s); } } } |
Output:
| Name:Anjali Name:Anu Name:Bala Name:Anu |
Removing Element from the ArrayList:
Elements can be removed from an arraylist using remove() method of the ArrayList class.
Syntax:
| remove(E e) |
The above method removes the first occurrence of the element ‘e’ from the array list.
Syntax:
| remove(int index) |
The above method removes the element from the index specified in the argument.
Example:
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public class ArrayListExample{ public static void main(String[] args) { ArrayList<String> al = new ArrayList<String>( Arrays.asList(“Anjali”, “Anu”,”Bala”,”Anu”)); //Initialize ArrayList using Arrays.asList() System.out.println(“ArrayList:”+al); System.out.println("Removing element in the position 2:"); al.remove(2); System.out.println(“ArrayList:”+al); System.out.println("Removing element ‘Anjali’ from the list:"); al.remove(“Anjali”); System.out.println("After Removal.."); Iterator<String> it = al.iterator(); //Displaying using Iterator interface while(it.hasNext()){ System.out.println(it.next()); } } |
Output:
| ArrayList: [Anjali,Anu,Bala,Anu]
Removing element in the position 2: ArrayList: [Anjali,Anu,Anu] Removing element ‘Anjali’ from the list: |
Finding the Length of the ArrayList:
The length of an ArrayList can be found using size() method of the ArrayList class.
Example:
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public class ArrayListExample{ public static void main(String[] args) { ArrayList<String> names = new ArrayList<String>( Arrays.asList(“Anjali”, “Anu”,”Bala”,”Anu”)); System.out.println(“Names:”+names); names.add(“Hari”); System.out.println(“Hari added to the list”); System.out.println(“Names:”+names); int size = names.size(); System.out.println(“Size after adding an element:”+size); } } |
Output:
| Names: [Anjali,Anu,Bala,Anu]
Hari added to the list Names: [Anjal,Anu,Bala,Anu,Hari] Size after adding an element:5 |
Methods of ArrayList:
| Methods of ArrayList | Description |
| boolean add(E e) | Appends the element e to the end of the list. |
| void add(int i, E element) | Inserts the element at the specified index ‘i’ in the list. |
| void clear() | Removes all the elements from the list. |
| boolean contains(Object o) | Returns true if the list contains the object specified. |
| E get(int index) | Returns the element at the specified index in the list. |
| boolean isEmpty() | Checks whether the list is empty. Returns true if the list has no elements |
| E remove(int index) | Removes the element at the specified index in the list. |
| E set(int index, E element) | Replaces the element at the specified index in the list with the element given. |
| int size() | Returns the number of elements in the list. |
| boolean addAll(Collection<? extends E> c) | Appends all of the elements in the specified collection to the end of the list. |
| boolean removeAll(Collection<?> c) | Removes all the elements that are contained in the specified collection from the ArrayList. |
| List<E> subList(int from, int to) | Returns a list which contains the elements between the specified positions. from – inclusive , to – exclusive. |