Java ArrayList
Java ArrayList is a class which extends AbstractList which implements List interface. ArrayList can store non-primitive data types as elements and form a list. ArrayList is an ordered list that means elements are arranged in the same order they are added.
- ArrayList may contain duplicate elements.
- ArrayList is not synchronized.
- ArrayList manipulation is slower than LinkedList because we have to do a lot of shifting once an element is removed.
- ArrayList dynamically increases its capacity based on requirement.
ArrayList Declaration
Non Generic Style
ArrayList myList = new ArrayList();
Generic Styles
ArrayList myList = new ArrayList(); //other way
ArrayList Constructors
Constructor | Description |
ArrayList() | Creates empty list |
ArrayList(Collection<? extends E> c) | ArrayList initialized with some collection. |
ArrayList(int capacity) | ArrayList with predefined capacity. |
ArrayList Methods
Methods | Detail |
void add(int index, E element) | Adds an element at specific index in list. |
boolean add(E e) | Adds an element in list. |
boolean addAll(Collection<? extends E> c) | Adds a collection in list. |
boolean addAll(int index, Collection<? extends E> c) | Ads a collection at a specifc index. |
void clear() | Clears list. |
void ensureCapacity(int requiredCapacity) | It is used to set or ensure list capacity. |
E get(int index) | Returns element of given index. |
boolean isEmpty() | Checks if list is empty |
Iterator() | Iterator |
listIterator() | listIterator |
int lastIndexOf(Object o) | Finds last index of object. |
Object[] toArray() | Converts to Array. |
T[] toArray(T[] a) | Returns Array. |
Object clone() | Creates shallow clone of list. |
boolean contains(Object o) | Checks if contains element. |
int indexOf(Object o) | Returns index of element. |
E remove(int index) | Removes the element at given index. |
boolean remove(Object o) | Removed object. |
boolean removeAll(Collection<?> c) | Removes all collection. |
boolean removeIf(Predicate<? super E> filter) | Removed based on condition. |
protected void removeRange(int fromIndex, int toIndex) | Removes range of elements. |
void replaceAll(UnaryOperator operator) | Replaces. |
void retainAll(Collection<?> c) | Retains all elements. |
E set(int index, E element) | Sets element at index. |
void sort(Comparator<? super E> c) | It sorts based on passed comparator. |
Spliterator spliterator() | It is used to create spliterator. |
List subList(int fromIndex, int toIndex) | It returns sub list based on index. |
int size() | Returns size. |
void trimToSize() | Trims to size. |
ArrayList Example With Iterating Using Iterator()
import java.util.*;
class ListExamples{
public static void main(String args[]){
//create list
ArrayList list=new ArrayList();
//add elemennts in list
list.add("Tom");
list.add("Bob");
Iterator itr=list.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}
}
}
Output
Tom
Bob
Iterating ArrayList or collection with forEach, for, ListIterator
and forEachRemaining
Example:
import java.util.ArrayList;
import java.util.ListIterator;
public class ArrayListExamples {
public static void main(String[] args) {
ArrayList myList=new ArrayList<>();
myList.add("John");
myList.add("Ron");
//foreach
myList.forEach(data->System.out.println("forEach: "+data));
//for
for (String data : myList) {
System.out.println("for: "+data);
}
//list itr
ListIterator ltr = myList.listIterator();
while(ltr.hasNext()) {
System.out.println("listIterator: "+ltr.next());
}
//forEachRemaining of iterator
ltr.forEachRemaining(data->{
System.out.println("forEachRemaining: "+data);
});
}
}
Output:
forEach: John
forEach: Ron
for: John
for: Ron
listIterator: John
listIterator: Ron
List/Collection examples of add, addAll, remove, removeAll and retainAll()
import java.util.ArrayList;
public class ArrayListExample2 {
public static void main(String[] args) {
ArrayList myList=new ArrayList<>();
ArrayList myList2=new ArrayList<>();
//add
myList.add("John");
myList.add("Ron");
myList.add("Jone");
myList.add("Tony");
myList2.add("Tony");
System.out.println(myList);
//addAll
myList.addAll(myList2);
//remove
myList.remove("John");
//removeAll
myList.removeAll(myList2);
System.out.println(myList);
//retainAll
myList.add("Tony");
myList.retainAll(myList2);
System.out.println(myList);
}
}
Output
[John, Ron, Jone, Tony]
[Ron, Jone]
[Tony]
Sorting the ArrayList
We can use collections class’ sorting methods to sort it.
Syntax:
Collections.sort();
Next Article
- LinkedList