List of objects Java
next prev Java ArrayListJava ArrayList class uses a dynamic array for storing the elements. It is like an array, but there is no size limit. We can add or remove elements anytime. So, it is much more flexible than the traditional array. It is found in the java.util package. It is like the Vector in C++. Show
The ArrayList in Java can have the duplicate elements also. It implements the List interface so we can use all the methods of List interface here. The ArrayList maintains the insertion order internally. It inherits the AbstractList class and implements List interface. The important points about Java ArrayList class are:
Hierarchy of ArrayList classAs shown in the above diagram, Java ArrayList class extends AbstractList class which implements List interface. The List interface extends the Collection and Iterable interfaces in hierarchical order. ArrayList class declarationLet's see the declaration for java.util.ArrayList class. Constructors of ArrayList
Methods of ArrayList
Java Non-generic Vs. Generic CollectionJava collection framework was non-generic before JDK 1.5. Since 1.5, it is generic. Java new generic collection allows you to have only one type of object in a collection. Now it is type safe so typecasting is not required at runtime. Let's see the old non-generic example of creating java collection. Let's see the new generic example of creating java collection. In a generic collection, we specify the type in angular braces. Now ArrayList is forced to have the only specified type of objects in it. If you try to add another type of object, it gives compile time error. For more information on Java generics, click here Java Generics Tutorial. Java ArrayList ExampleTest it NowOutput: [Mango, Apple, Banana, Grapes]
Iterating ArrayList using IteratorLet's see an example to traverse ArrayList elements using the Iterator interface. Test it NowOutput: Mango
Apple
Banana
Grapes
Iterating ArrayList using For-each loopLet's see an example to traverse the ArrayList elements using the for-each loop Output: Test it NowMango
Apple
Banana
Grapes
Get and Set ArrayListThe get() method returns the element at the specified index, whereas the set() method changes the element. Test it NowOutput: Returning element: Apple
Mango
Dates
Banana
Grapes
How to Sort ArrayListThe java.util package provides a utility class Collections which has the static method sort(). Using the Collections.sort() method, we can easily sort the ArrayList. Output: Apple
Banana
Grapes
Mango
Sorting numbers...
1
11
21
51
Ways to iterate the elements of the collection in JavaThere are various ways to traverse the collection elements:
Iterating Collection through remaining waysLet's see an example to traverse the ArrayList elements through other ways Output: Traversing list through List Iterator:
Ajay
Ravi
Vijay
Ravi
Traversing list through for loop:
Ravi
Vijay
Ravi
Ajay
Traversing list through forEach() method:
Ravi
Vijay
Ravi
Ajay
Traversing list through forEachRemaining() method:
Ravi
Vijay
Ravi
Ajay
User-defined class objects in Java ArrayListLet's see an example where we are storing Student class object in an array list. Output: 101 Sonoo 23
102 Ravi 21
103 Hanumat 25
Java ArrayList Serialization and Deserialization ExampleLet's see an example to serialize an ArrayList object and then deserialize it. Output: [Ravi, Vijay, Ajay]
Java ArrayList example to add elementsHere, we see different ways to add an element. Output: Initial list of elements: []
After invoking add(E e) method: [Ravi, Vijay, Ajay]
After invoking add(int index, E element) method: [Ravi, Gaurav, Vijay, Ajay]
After invoking addAll(Collection c) method:
[Ravi, Gaurav, Vijay, Ajay, Sonoo, Hanumat]
After invoking addAll(int index, Collection c) method:
[Ravi, John, Rahul, Gaurav, Vijay, Ajay, Sonoo, Hanumat]
Java ArrayList example to remove elementsHere, we see different ways to remove an element. Output: An initial list of elements: [Ravi, Vijay, Ajay, Anuj, Gaurav]
After invoking remove(object) method: [Ravi, Ajay, Anuj, Gaurav]
After invoking remove(index) method: [Ajay, Anuj, Gaurav]
Updated list : [Ajay, Anuj, Gaurav, Ravi, Hanumat]
After invoking removeAll() method: [Ajay, Anuj, Gaurav]
After invoking removeIf() method: [Anuj, Gaurav]
After invoking clear() method: []
Java ArrayList example of retainAll() methodOutput: iterating the elements after retaining the elements of al2
Ravi
Java ArrayList example of isEmpty() methodOutput: Is ArrayList Empty: true
After Insertion
Is ArrayList Empty: false
Java ArrayList Example: BookLet's see an ArrayList example where we are adding books to list and printing all the books. Test it NowOutput: 101 Let us C Yashwant Kanetkar BPB 8
102 Data Communications and Networking Forouzan Mc Graw Hill 4
103 Operating System Galvin Wiley 6
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