Adding all elements in an array java

Java ArrayList add array example

Java ArrayList add array example shows how to add all elements of an array to ArrayList in Java. The example also shows how to add array to ArrayList using various ways.

How to add Array to ArrayList in Java?

There are various ways to add an array to ArrayList in Java.

1) Using the addAll method of Collections class

You can use addAll method of Collections class to add array to ArrayList.

This method adds all specified elements to the argument collection.

Example

2) Using the asList method of Arrays class and addAll method of ArrayList

You can use asList method of Arrays class to convert an array to the List object first.

This method returns a fixed size List object backed by the original argument array.

Once you get the List object, you can add the list object to the ArrayList using addAll method of ArrayList.

This method adds all elements of the specified collection at the end of the ArrayList object.

Example

What is the preferred way to add array to ArrayList?

Using addAll method of Collections class (approach 1) is preferred over using asList method of Arrays and addAll method of ArrayList class (approach 2) because it is faster in terms of performance under most implementation.

This example is a part of the ArrayList in Java tutorial and Array in Java tutorial.

Please let me know your views in the comments section below.

About the author

I have a master’s degree in computer science and over 18 years of experience designing and developing Java applications. I have worked with many fortune 500 companies as an eCommerce Architect. Follow me on LinkedIn and Facebook.

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How to Add Elements to an Array in Java

Array is a group of same data type elements and is considered a fixed-size data structure. In Java, you cannot directly add elements to an array because the location next to the last element of the array is available in memory or not is not known. However, there are some other ways for adding elements to an array.

This blog will explain how to add an element to an array in Java. So let’s get started!

Adding elements to a Java array

In Java, you can add elements to an array:

Now, let’s check out the stated method one by one.

Method 1: Adding Elements to array by creating a new Java array

To add elements to an array in Java, first create an array then copy the existing array elements in the newly created array. After doing so, you can add new elements to it.

Example
In this example, firstly, we will create an integer array named numArray[ ] with the following values:

In the next step, we will create a new integer type array named newNumArray[ ] with a greater size of the existing array:

The element 77 is stored in the variable named appendValue, which we want to add:

For printing the array numArray[ ], use the System.out.println() method:

Now, copy the elements of array numArray[ ] in a newly created array newNumArray[ ] by using a for loop:

Then, insert the value that is stored in appendValue variable in the newNumArray[ ]:

Lastly, print the newNumArray[] elements:

The given output indicates that 77 is successfully added in the newNumArray[ ]:

Now, let’s check out the other method for adding elements to an array in Java.

Method 2: Adding Elements to an array in Java by using ArrayList

You can also utilize Java ArrayList to add elements to an array. It is considered ideal as ArrayList is a re-sizable array.

Example
First of all, we will create an integer type array named numArray[ ] with the following values:

Print array by using the System.out.println() method:

Create an ArrayList named newNumArrayList and pass the array in it by using the aslist() method:

Add the required element in the created ArrayList with the help of the add() method:

Now, we will convert this ArrayList into an array by using the toArray() method:

Finally, print the array with the appended element:

Output

We have provided all of the necessary information related to adding elements to an array in Java.

Conclusion

In Java, elements can be added to an array by using Array List or creating a new array. The best and most efficient method is utilizing the ArrayList for the mentioned purpose. To do so, convert the existing array into an ArrayList, add required elements, and then convert it to a normal array. ArrayList also takes less memory space. This blog discussed the methods of adding elements to an array in Java.

About the author

Farah Batool

I completed my master’s degree in computer science. I am an academic researcher and love to learn and write about new technologies. I am passionate about writing and sharing my experience with the world.

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Add Multiple Items to Java ArrayList

Learn to add multiple items to an ArrayList in a single statement using simple-to-follow Java examples.

1. Using List.of() or Arrays.asList() to Initialize a New ArrayList

To initialize an ArrayList with multiple items in a single line can be done by creating a List of items using either Arrays.asList() or List.of() methods. Both methods create an immutable List containing items passed to the factory method.

In the given example, we add two strings, “a” and “b”, to the ArrayList.

ArrayList arrayList = new ArrayList<>(Arrays.asList("a", "b")); //or ArrayList arrayList = new ArrayList<>(List.of("a", "b"));

2. Using Collections.addAll() to Add Items from an Existing ArrayList

To add all items from another collection to this ArrayList, we can use Collections.addAll() method that adds all of the specified items to the given list. Note that the items to be added may be specified individually or as an array.

ArrayList arrayList = new ArrayList<>(Arrays.asList("a", "b")); Collections.addAll(arrayList, "c", "d"); System.out.println(arrayList); //[a, b, c, d]

Alternatively, we can use ArrayList constructor that accepts a collection and initializes the ArrayList with the items from the argument collection. This can be useful if we add the whole collection into this ArrayList.

List namesList = Arrays.asList( "a", "b", "c"); ArrayList instance = new ArrayList<>(namesList);

3. Using Stream API to Add Only Selected Items

This method uses Java Stream API. We create a stream of elements from the first list, add a filter() to get the desired elements only, and then add the filtered elements to another list.

//List 1 List namesList = Arrays.asList( "a", "b", "c"); //List 2 ArrayList otherList = new ArrayList<>(Arrays.asList( "d", "e")); //Do not add 'a' to the new list namesList.stream() .filter(name -> !"a".equals(name)) .forEachOrdered(otherList::add); System.out.println(otherList); //[d, e, b, c]

In the above examples, we learned to add multiple elements to ArrayList. We have added all elements to ArrayList, and then we saw the example of adding only selected items to the ArrayList from the Java 8 stream API.

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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.

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