Dynamic lists in java

Dynamic Array Java Example

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. The length is fixed after creation. In this article, we will show Java dynamic arrays.

A dynamic array is a variable-size list data structure that allows elements to be added or removed. Dynamic arrays overcome a limit of static arrays, which have a fixed capacity that needs to be specified at allocation.

Let’s now discuss the dynamic array and its implementations in Java (Vector, ArrayList, LinkedList, CopyOnWriteArrayList).

1. Dynamic array

A simple dynamic array can be constructed by allocating an array of fixed size, typically larger than the number of elements immediately required. The elements of the dynamic array are stored at the start of the underlying array, and the remaining positions towards the end of the array are reserved or unused. Elements can be added at the end of the dynamic array by using reserved space until the space is completely consumed. The underlying fixed-size array needs to be increased in size when further elements have to be added after all the space is consumed. Typically resizing is expensive as it involves allocating a new array and copying each element from the original array (costs O(n) time).

A fixed-size array will suffice in scenarios where the maximum logical size is fixed. A dynamic array will be needed when the maximum logical size is unknown initially, or likely to change.

2. Features of Dynamic Array

Key features of a dynamic array are adding, deleting, and resizing an element. Let us now check these features.

2.1 Add an element to a dynamic array

As discussed in the previous section, elements are added at the end of an array. A new array (typically double the original array size) is created and data is copied from the original array to the new one after the allocated space is consumed.

2.2 Delete an element from a dynamic array

The remove(i) removes the element at index location – ‘i’ and shifts all the elements at the right side of the index to left.

2.3 Resize an array

An array’s size can be increased or decreased. Resizing is usually an expensive operation, as it would mean creating a new array and copying all the elements (costs O(n) time).

2.4 Table for complexity O(n)

A dynamic array automatically grows when you try to make insertion and there is no more space left for the new item. Usually, the array doubles in size. In this case, a new array has to be created with double the size of the previous one and copy all the elements to the new one. This will take O(n), but a simple insertion on an empty cell costs only O(1). This is also true when we are trying to remove an element.

Also if we want to search the array, giving the index takes only O(1). If we search by the value we have to parse all the array so the worst-case scenario is O(n).

4. Built-in Dynamic arrays in Java

Java has built-in dynamic arrays. These are Vector, ArrayList, LinkedList and CopyOnWriteArrayList.

ArrayList is a resizable array implementation of the List interface. It 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. Note that this implementation is not synchronized.

The Vector class implements a growable array of objects. Like an array, it contains components that can be accessed using an integer index. The size of a Vector can grow or shrink as needed to accommodate adding or removing items after Vector has been created. Unlike the new collection implementations, Vector is synchronized. if a thread-safe implementation is not needed, it is recommended to use ArrayList in place of Vector.

The LinkedList is a doubly-linked list implementation of the List and Deque interfaces. It implements all optional list operations and permits all elements (including null). Note that this implementation is not synchronized.

The CopyOnWriteArrayList is a thread-safe variant of ArrayList in which all mutative operations (add, set, and so on) are implemented by making a fresh copy of the underlying array. This is costly, but more efficient when traversals operations vastly outnumber mutations. All elements (including null) are permitted. The snapshot style iterator method uses a reference to the state of the array at the point that the iterator was created. This array never changes during the lifetime of the iterator, and hence interference is impossible.

5. Download the source code

This was an example for Dynamic arrays.

Last updated on Oct. 14th, 2021

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Java Dynamic List || Java example

In the previous tutorial we have seen a static list declaration and usage with different types of data types.Now in this part of the tutorial we will get to know a dynamic list.

Java Dynamic List :

When we create any real time application like shopping app where cart is designed or storing users as contact’s or fetching data from databases we use list.

And now we can’t assess the list size so we need to use java dynamic list’s to fulfill the requirement.

ArrayList list = new ArrayList<>();

Now we will try to add 10 String’s into the Array List here there is no limit of String’s we can add more than 10 String too.

list.add("One"); list.add("Two"); . . . . list.add("Ten");

Using a for loop we can parse the loop based on the index position

String Array List:

public static ArrayList list = new ArrayList<>(); public static void main(String args[]) < list.add("One"); list.add("Two"); list.add("Three"); list.add("Four"); list.add("Five"); list.add("Six"); list.add("Seven"); list.add("Eight"); list.add("Nine"); list.add("Ten"); for(int i = 0; i < list.size(); i++)< System.out.println(list.get(i)); >>

Integer Array List:

ArrayList list = new ArrayList<>();

list.add(1); list.add(2); list.add(3); list.add(4); list.add(5);

public static ArrayList list = new ArrayList<>(); public static void main(String args[]) < list.add(1); list.add(2); list.add(3); list.add(4); list.add(5); for (int i = 0; i < list.size(); i++) < System.out.println(list.get(i)); >>

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Dynamic Array in Java

We know that arrays are linear and homogeneous data structures that have a fixed size. While creating an array, we have to specify its size which cannot be changed once array is created at runtime. This creates an issue if we do not have an upper limit on the number of elements in an array.

This issue can be resolved using dynamic arrays or ArrayList in Java. The size of the ArrayList is dynamic which means it can be modified at runtime. ArrayList is a part of Java Collections framework and is present in java.util package.

Introduction to Dynamic Array in Java

We all are familiar with Array data structure. It is one of the most commonly used data structures in all programming languages.

• linear (store elements in a sequential order),
• homogeneous (can store elements of the same type) and
• contiguous (allocate consecutive blocks of memory to the elements)

data structures. Arrays have a fixed size and it has to be specified at the time of creation. This causes a menace when we want to add elements beyond its initial size at runtime.

In this scenario, we have to create a new array with a bigger size and copy the elements of the previous array to the newly created array. This not just wastes time, but also wastes a lot of memory.

Solution

In order to mitigate the sizing problem of the array, dynamic arrays came into the picture. ArrayList data structure is used to implement the concept of dynamic data structures in Java. As the name suggests, dynamic arrays have a dynamic size modifiable at runtime. We do not have to specify the size of the ArrayList at the time of creation .

Advantages of Dynamic Arrays:

• Variable size: We do not need to specify the initial size, it is variable in nature according to the elements inserted or deleted.
• Constant look-up time: When the element has to be retrieved at a given index, ArrayList takes O(1) time same as conventional arrays.
• Cache friendly: Dynamic arrays also put elements in a contiguous manner which results in an efficient cache utilization.

Disadvantage of Dynamic Arrays:

O(N) time complexity: The worst case time complexity of adding an element to an ArrayList data structure is O ( N ) O(N) O ( N ) when a new array has to be created and all the elements copied to it.

Working of Dynamic Array in Java

The default capacity of dynamic arrays in Java is 10 . That means internally, a dynamic array with an internal capacity 10 is created. Whenever a user inserts an element in the dynamic array, its size increases.

When the size of the dynamic array becomes equal to its capacity, a new array with double the capacity gets created and the previous elements are stored inside the new array created internally.

Size vs. Capacity

Capacity is the current maximum number of elements a dynamic array can hold, whereas Size is the total elements present in the dynamic array.

In the example, above the array can solve a maximum of 9 elements. However, currently it holds 6 elements. Hence, it has a capacity of 9 and size of 6 .

Creating a Dynamic Array in Java

Syntax of ArrayList Declaration:

Using this, we can create an ArrayList of that specific data type whose initial capacity is 10.

Explanation:

We have created a dynamic array i.e., an ArrayList of integers arr and then checked its size. Since the ArrayList has no elements added, its size is 0 at present. When the elements are added, their size increases.

Add Element in a Dynamic Array

To add an element in a dynamic array, we use the add() function.

To add an Integer elem to the ArrayList arr declared above, we can use the following statement:

Explanation:

We have created an ArrayList i.e., a dynamic array and added elements to it. We can see that after the elements are added, the size of the dynamic array increases.

Resizing a Dynamic Array in Java

As discussed before, when dynamic arrays are created, its internal implementation uses an array. So, at a point when the size of the dynamic array becomes equal to its capacity, a new array with a double size is created.

This is a snippet showing the internal resizing:

Dynamic Array with ArrayList

Now we will see an example where we can perform some operations on the dynamic array.

Explanation:

We have created a dynamic array i.e. ArrayList arr and we have performed several operations like adding, removing and getting an element.

We cannot find the capacity of a ArrayList data structure.

Conclusion

• Arrays have a fixed size so it takes a lot of operations and memory to resize them.
• Dynamic arrays are dynamic in size. We do not have to specify the size of the ArrayList at the time of creation.
• Dynamic array is also known as ArrayList in Java.
• Dynamic arrays in Java have a variable size, and constant lookup time and are cache-friendly.
• The initial capacity of the ArrayList is 10 and when the size becomes 10, it resizes.

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Dynamic lists in java

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