How to add to array java

Java add to array

In this post, we will see how to add elements to the array.

Using Apache’s common lang library

You can use varargs add method to add elements to array dynamically.

Here are the few add overloaded methods provided by ArrayUtils class

If you want to add more than one element, you can use ArrayUtils’s addAll methods.

Here is quick example using ArrayUtil’s add method

When you run above program, you will get below output.

By writing your own utility method

As Array is fixed in length, there is no direct method to add elements to the array, you can write your own utility method.
We have used varargs here to support n numbers of elements that can be added to array.

When you run above program, you will get below output:

As you can see, we are using object[] here. If you want to write a method specific to any data type, you can write that as well.
If you have frequent scenarios to add elements to array dynamically, I would recommend to use varargs instead of Array.

That’s all about Java add to array.

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How to add and remove Elements from an Dynamic Array in Java? Example Tutorial

Java beginners often ask how to add new elements to an array in Java? or how to remove elements from an array in Java? is that possible in Java? Well, no, it’s not possible in Java because arrays length cannot be changed once created. This means neither you can add new elements nor you can remove an old one from an array in Java. All you can do is reassign values to a different bucket. For example, if you have a string array of length 3 like <"java", "is", "great">then you can just replace the individual index to make it like <"Python", "is", "great">by replacing «java» with «Python» at first index, but you cannot add or remove elements.

An important thing to remember is that when we say we add an element into an array, we mean that its length increased by one and when deleting an element, its length should go down by 1, which is not possible because the length of the array is constant and cannot be changed once created. That’s also the main difference between an array and a linked list data structure.

Then the bigger question comes? What do we do? if we have an array of active users and new user logs in how do we store that into an array? how do we remove a user when he logs out.

Well, you can use ArrayList instead of an array, which allows you to add or remove elements. It’s like a dynamic array that can grow and shrink in size if needed. In this article, I will show you how to add and remove elements from an ArrayList in Java.

Btw, If you are a beginner then you should go through a comprehensive course like The Complete Java Master Class for Beginners to learn about essential classes from JDK, especially the Java Collection Framework.

How to add and remove Objects from ArrayList in Java

Here is a code example to add and remove elements from an ArrayList in Java:

From the output, you can see that the ArrayList changes after you add or remove elements. Their size also changes like initially when you create an ArrayList the size is zero but once you add one element is incremented to 1 and goes up to 3 and then you start removing elements its size started to decrease and finally becomes zero one all elements were removed.

The size() method returns is a number of elements in ArrayList, you can get this by calling the size() method. It’s very different from the length of the Array, which never changes after you create the array. You can further check out Java Fundamentals: Collections course on Pluralsight to learn more about essential collection classes in Java-like List, Set, Map, etc. This course is created by Java champion Richard Warburton.

That’s all about how to add/remove elements into an array in Java. As I said, it’s not possible because the length of the array cannot be changed. Apart from using ArrayList, a kind of dynamic array, only another option you have is to create a new array every time you add or remove an element and copy elements from the old array to the new one, which is not an ideal solution.

It would result in so many temporary array objects. Also copying elements from one array to another is a very expensive operation especially for large arrays. In short, use ArrayList if you need a dynamic array in Java.

Add New Elements to an Array in Java

This tutorial discusses how to add new elements to an array in Java.

Array in Java is a container object which holds a fixed number of elements of the same data type. The length of the array is defined while declaring the array object, and can not be changed later on.

Suppose we have an array of length 5 in Java instantiated with some values:

Now there is a requirement to add a 6th element to our array. Let’s try to add this 6th element to our array.

The above line of code gives the following error:

This is because we declared the array to be of size 5 initially and we tried to add a 6th element to it.

Please enable JavaScript

Not to worry, there are 2 possible solutions to get this done. We can use an ArrayList instead of an array or create a new larger array to accommodate new elements.

Use an ArrayList

The above code outputs the following.

Or if we already have an array, we can also create an ArrayList directly.

The above code outputs the following.

We can easily convert an ArrayList back to an array.

Create a New Larger Array

If we are insistent on working with arrays only, we can use the java.util.Arrays.copyOf method to create a bigger array and accommodate a new element. Let us use the array arr we created above and add a new element to it in the example below.

The above code outputs the following.

Therefore this solution is not recommended because the addition of every new element has a time complexity of O(n) since it has to copy all the elements from the previous array to a new array. On the other hand, the addition of every new element using ArrayList has O(1) amortized cost per operation.

Add Elements to Array and ArrayList in Java

An array is a fixed-size collection of similar objects in Java. An ArrayList is very similar to an array but has no size restrictions.

In this tutorial, we will learn how to insert elements in arrays and ArrayLists.

Difference Between Array and ArrayList

Before learning how to insert elements, let’s first take a quick look at some of the differences between arrays and ArrayLists.

Implementation

An Array is a simple, linear data structure provided by Java. ArrayList is a class in Java that implements the List interface, and it is part of the Collections Framework. ArrayList internally uses an Array for its operations.

Accessing and Modifying Elements

Elements of an array are accessed and modified by using indexes. The ArrayList class provides getter and setter methods to access and modify its content.

Element Types

Arrays are capable of storing primitive as well as non-primitive types. ArrayLists can only store non-primitive types. However, we can use wrapper classes to store primitives.

As discussed above, arrays are of fixed size, while ArrayLists have dynamic size. For an array, we need to define its size during instantiation. We cannot exceed this size limit. For ArrayLists, the size dynamically increases when we need to add more elements to it. A new underlying array of larger size is created to accommodate the additional items.

Appending Elements

Let’s learn how to append elements to an array and ArrayList. Append means to add to the end.

Appending to Arrays

We will first create a new array of larger size. Next, we will transfer the elements to this new array. Finally, we can add the new item at the end of this new array. The following code demonstrates this.

Initial Array: [1, 2, 3, 4, 5, 6]
After adding the element: [1, 2, 3, 4, 5, 6, 7, 8, 9]

The Arrays class provides a simple copyOf() method that copies the elements from the old array to the new one. This method takes the old array and the new array’s size as parameters. Let’s rewrite the above code by using the copyOf() method instead of a for loop.

Initial Array: [1, 2, 3, 4, 5, 6]
After adding the element: [1, 2, 3, 4, 5, 6, 7, 8, 9]

Appending to ArrayList

Appending to an ArrayList is pretty straightforward. This class comes with an add() method that adds an element to the end of the list. The following code demonstrates this.

ArrayList: [1, 2, 3]

Inserting Elements

Let’s now try to insert elements at any index. Make sure that the index is within the bounds to avoid the IndexOutOfBoundsException. We will

Inserting in an Array

First, we will create a new array to accommodate the additional element. To insert at a given index, we need to shift the element present at that index and all elements after this index one place to the right.

For example, consider the initial array [10, 20, 30, 40], and we need to insert 50 at index 1. The elements 20, 30, and 40 will shift one place to the right. The resulting array will be [10, 50, 20, 30, 40].

Initial Array: [10, 20, 30, 40]
After adding 50 at index 1: [10, 50, 20, 30, 40]

Inserting in an ArrayList

The add() method has an overloaded version which also takes the index where we want to add an element. The items are moved from one place to the right to make space for the new item.

Initial ArrayList: [10, 20, 30, 40]
After adding 50 at index 1: [10, 50, 20, 30, 40]

Summary

Inserting elements in an array is quite complicated. We need to create a new array and transfer the contents of the old one. However, an ArrayList provides a convenient add() method to append or insert elements. Make sure to a valid index to avoid an index-out-of-bounds error. Note that the add() method has a worst-case time complexity of O(N). It is because of the creation of a new underlying array.

Arrays

An array is a container object that holds a fixed number of values of a single type. The length of an array is established when the array is created. After creation, its length is fixed. You have seen an example of arrays already, in the main method of the «Hello World!» application. This section discusses arrays in greater detail.

An array of 10 elements.

Each item in an array is called an element, and each element is accessed by its numerical index. As shown in the preceding illustration, numbering begins with 0. The 9th element, for example, would therefore be accessed at index 8.

The output from this program is:

Declaring a Variable to Refer to an Array

The preceding program declares an array (named anArray ) with the following line of code:

Similarly, you can declare arrays of other types:

You can also place the brackets after the array’s name:

However, convention discourages this form; the brackets identify the array type and should appear with the type designation.

Creating, Initializing, and Accessing an Array

One way to create an array is with the new operator. The next statement in the ArrayDemo program allocates an array with enough memory for 10 integer elements and assigns the array to the anArray variable.

If this statement is missing, then the compiler prints an error like the following, and compilation fails:

The next few lines assign values to each element of the array:

Each array element is accessed by its numerical index:

Alternatively, you can use the shortcut syntax to create and initialize an array:

Here the length of the array is determined by the number of values provided between braces and separated by commas.

In the Java programming language, a multidimensional array is an array whose components are themselves arrays. This is unlike arrays in C or Fortran. A consequence of this is that the rows are allowed to vary in length, as shown in the following MultiDimArrayDemo program:

The output from this program is:

Finally, you can use the built-in length property to determine the size of any array. The following code prints the array’s size to standard output:

Copying Arrays

The System class has an arraycopy method that you can use to efficiently copy data from one array into another:

The two Object arguments specify the array to copy from and the array to copy to. The three int arguments specify the starting position in the source array, the starting position in the destination array, and the number of array elements to copy.

The output from this program is:

Array Manipulations

Arrays are a powerful and useful concept used in programming. Java SE provides methods to perform some of the most common manipulations related to arrays. For instance, the ArrayCopyDemo example uses the arraycopy method of the System class instead of manually iterating through the elements of the source array and placing each one into the destination array. This is performed behind the scenes, enabling the developer to use just one line of code to call the method.

For your convenience, Java SE provides several methods for performing array manipulations (common tasks, such as copying, sorting and searching arrays) in the java.util.Arrays class. For instance, the previous example can be modified to use the copyOfRange method of the java.util.Arrays class, as you can see in the ArrayCopyOfDemo example. The difference is that using the copyOfRange method does not require you to create the destination array before calling the method, because the destination array is returned by the method:

As you can see, the output from this program is the same, although it requires fewer lines of code. Note that the second parameter of the copyOfRange method is the initial index of the range to be copied, inclusively, while the third parameter is the final index of the range to be copied, exclusively. In this example, the range to be copied does not include the array element at index 9 (which contains the string Lungo ).

Some other useful operations provided by methods in the java.util.Arrays class are:

Searching an array for a specific value to get the index at which it is placed (the binarySearch method).

Comparing two arrays to determine if they are equal or not (the equals method).

Filling an array to place a specific value at each index (the fill method).

Sorting an array into ascending order. This can be done either sequentially, using the sort method, or concurrently, using the parallelSort method introduced in Java SE 8. Parallel sorting of large arrays on multiprocessor systems is faster than sequential array sorting.

Creating a stream that uses an array as its source (the stream method). For example, the following statement prints the contents of the copyTo array in the same way as in the previous example:

See Aggregate Operations for more information about streams.

Converting an array to a string. The toString method converts each element of the array to a string, separates them with commas, then surrounds them with brackets. For example, the following statement converts the copyTo array to a string and prints it: