Class ArrayList
Type Parameters: E — the type of elements in this list All Implemented Interfaces: Serializable , Cloneable , Iterable , Collection , List , RandomAccess Direct Known Subclasses: AttributeList , RoleList , RoleUnresolvedList
Resizable-array implementation of the List interface. Implements all optional list operations, and permits all elements, including null . In addition to implementing the List interface, this class provides methods to manipulate the size of the array that is used internally to store the list. (This class is roughly equivalent to Vector , except that it is unsynchronized.)
The size , isEmpty , get , set , iterator , and listIterator operations run in constant time. The add operation runs in amortized constant time, that is, adding n elements requires O(n) time. All of the other operations run in linear time (roughly speaking). The constant factor is low compared to that for the LinkedList implementation.
Each ArrayList instance has a capacity. The capacity is the size of the array used to store the elements in the list. It is always at least as large as the list size. As elements are added to an ArrayList, its capacity grows automatically. The details of the growth policy are not specified beyond the fact that adding an element has constant amortized time cost.
An application can increase the capacity of an ArrayList instance before adding a large number of elements using the ensureCapacity operation. This may reduce the amount of incremental reallocation.
Note that this implementation is not synchronized. If multiple threads access an ArrayList instance concurrently, and at least one of the threads modifies the list structurally, it must be synchronized externally. (A structural modification is any operation that adds or deletes one or more elements, or explicitly resizes the backing array; merely setting the value of an element is not a structural modification.) This is typically accomplished by synchronizing on some object that naturally encapsulates the list. If no such object exists, the list should be «wrapped» using the Collections.synchronizedList method. This is best done at creation time, to prevent accidental unsynchronized access to the list:
List list = Collections.synchronizedList(new ArrayList(. ));
The iterators returned by this class’s iterator and listIterator methods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the iterator’s own remove or add methods, the iterator will throw a ConcurrentModificationException . Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.
Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.
This class is a member of the Java Collections Framework.
Add an Object in an Arraylist in Java
- Add Objects of the Same Type in an ArrayList
- Add Objects of Different Types in an ArrayList
In Java, ArrayList is a resizable array and can also be defined as an ordered sequence of elements. Unlike simple arrays, the Java ArrayList is more flexible and can hold multiple data types. This article will demonstrate how you can utilize this function.
Add Objects of the Same Type in an ArrayList
Here, we will add user-defined or custom class objects to an ArrayList . In ArrayList , we can access the elements using the integer index. We’ll specify or declare the type of object we will store in the ArrayList inside the <> (angle brackets).
In the code below, we have a Book class object with a constructor and three instance variables bookName , author , and rating of data type, respectively. We create a Book class object using the new keyword followed by the constructor call with the parameters; this assigns the passed value to the instance variables.
The add() method inserts objects into the arrayofBooks . Thus, we added 4 Book class objects to our arrayOfBooks . We then run a foreach loop to iterate and display all the Book data.
We can access the attributes of the Book class by using the . dot operator. Below we accessed the bookName attribute by calling the book.bookName function.
import java.util.ArrayList; public class ArrayObject public static void main (String args[]) ArrayListBook> arrayOfBooks = new ArrayList<>(); arrayOfBooks.add(new Book("To Kill a Mockingbird", "Harper Lee", 3)); arrayOfBooks.add(new Book("1984", "George Orwell", 4)); arrayOfBooks.add(new Book("Harry Potter and the Philosopher's Stone", "J.K. Rowling", 4)); arrayOfBooks.add(new Book("The Lord of the Rings", "J.R.R. Tolkien", 4.5)); for (Book book: arrayOfBooks) System.out.println("BookTitle: "+book.bookName+", by"+book.author+ "with a rating of "+book.rating); > > > class Book String bookName; String author; double rating; Book(String bookName, String author, double rating) this.bookName = bookName; this.author = author; this.rating = rating; > > BookTitle: To Kill a Mockingbird, byHarper Leewith a rating of 3.0 BookTitle: 1984, byGeorge Orwellwith a rating of 4.0 BookTitle: Harry Potter and the Philosopher's Stone, byJ.K. Rowlingwith a rating of 4.0 BookTitle: The Lord of the Rings, byJ.R.R. Tolkienwith a rating of 4.5 Add Objects of Different Types in an ArrayList
As mentioned, the function ArrayList can also hold multiple types of objects. Here, arrayOfDifferentObject is an ArrayList that can hold objects of different types. We declared our ArrayList using the class in the syntax given below in code.
In Java, ArrayList can hold objects of wrapper classes like double, integer, and string.
We then add elements to the ArrayList using the add() method. Firstly, we added a string value to our ArrayList , then a double value, integer, and float, respectively. We can also replace an element with a new value at the index of our choice using the set() method.
We replaced the arrayOfDifferentObject.set(1,»David Wells») and the double value at index 1 with a string value. After that, we can see that the output is modified.
import java.util.ArrayList; public class ArrayObject public static void main (String args[]) ArrayListObject> arrayOfDifferentObject = new ArrayListObject>(); arrayOfDifferentObject.add("John Doe"); arrayOfDifferentObject.add(10.00D); arrayOfDifferentObject.add(10); arrayOfDifferentObject.add(10.11F); System.out.println("ArrayList after all insertion:-"); for (int i=0; iarrayOfDifferentObject.size(); i++) System.out.println(arrayOfDifferentObject.get(i)); > arrayOfDifferentObject.set(1,"David Wells"); System.out.println("ArrayList after modification:-"); for (int i=0; iarrayOfDifferentObject.size(); i++) System.out.println(arrayOfDifferentObject.get(i)); > > > ArrayList after all insertion:- John Doe 10.0 10 10.11 ArrayList after modification:- John Doe David Wells 10 10.11 Rupam Saini is an android developer, who also works sometimes as a web developer., He likes to read books and write about various things.