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Link to the GitHub repository which has all the basic operations of Array List in Java: SkillYaan | Array List | Demo in Java
What is an ArrayList? What are some differences between Arrays and
ArrayLists?
An ArrayList is a dynamic data structure in Java that allows for resizing as needed. It can be used to manage collections of data and is commonly implemented in applications such as
e-commerce or user interfaces. Common operations that can be performed on an ArrayList include adding or removing elements, getting or setting elements at a specific index, and iterating over the elements in the list. In interviews, questions may be asked about ArrayLists, such as the differences between ArrayLists and Arrays and when to use one over the other. Overall, ArrayLists are an efficient and flexible way to manage collections of data in Java programming.
An ArrayList is a dynamic data structure in Java that is similar to an array, but with the added ability to dynamically resize itself as needed. It is part of the Java Collections Framework and is implemented using an array internally.
Differences between Array and ArrayList
In summary, Arrays and ArrayLists are both data structures in Java used for storing collections of elements, but they differ in several key ways.
Arrays are fixed in size, require a size to be specified at initialization, and use contiguous blocks of memory to store elements, whereas ArrayLists are dynamic in size, do not require a size to be specified, and use non-contiguous blocks of memory to store elements. ArrayLists are generally more efficient than Arrays for adding or removing elements, but may be slightly slower for simple element retrieval.
The ArrayList class in Java provides a variety of methods to perform operations on the list, such as adding or removing elements, getting or setting elements at a specific index, and iterating over the elements in the list.
Overall, ArrayLists are a flexible and efficient data structure for managing collections of elements where the size of the collection may change over time.
Internal implementation of Array Lists, Operations on Array lists, Concept of default and logical capacity.
Internal implementation of Array Lists: In Java, ArrayLists are implemented internally using arrays of objects. When an ArrayList is created, it creates an internal array with a default capacity (which is 10 by default but may vary depending on JAVA version). As elements are added to the ArrayList, the internal array is resized as needed.
Here's a brief overview of the internal implementation of ArrayLists in Java
The ArrayList class contains a private instance variable named elementData, which is an Object array that stores the elements in the list.
When an ArrayList is created, it initializes the elementData array with a default capacity say 10.
When an element is added to the ArrayList, the add() method first checks whether the elementData array is full. If the array is full, it creates a new array with a larger capacity and copies the existing elements to the new array.
The add() method then adds the new element to the end of the elementData array.
When an element is removed from the ArrayList using the remove() method, the method first removes the element from the elementData array and then shifts all the subsequent elements one position to the left to fill the gap.
When the trimToSize() method is called on an ArrayList, it resizes the elementData array to match the size of the list, which can be useful for reducing memory usage when the list is smaller than its current capacity.
The ensureCapacity() method can be used to increase the capacity of the elementData array, which can be useful for improving performance when you know that the list will be growing in size.
Overall, the internal implementation of ArrayLists in Java is optimized for dynamic resizing and efficient element access, which makes them a popular choice for managing collections of elements where the size of the collection may change over time.
Some of the common operations that can be performed on an ArrayList in Java include:
Adding elements: Elements can be added to the end of the list using the add() method or inserted at a specific index using the add(index, element) method.
Removing elements: Elements can be removed from the list using the remove() method or removed at a specific index using the remove(index) method.
Getting elements: Elements can be retrieved from the list using the get() method, which returns the element at a specific index.
Setting elements: Elements can be updated in the list using the set() method, which sets the element at a specific index to a new value.
Iterating over elements: Elements can be accessed and processed in a loop using various methods such as the forEach() method, the iterator(), or the listIterator() method.
Here are some advanced operations that can be performed on ArrayLists:
Removing duplicates: ArrayLists can be used to remove duplicate elements in the list by iterating through the list and removing the duplicates.
Sorting: ArrayLists can be sorted using the Collections.sort() method or by implementing the Comparable or Comparator interfaces.
Sublist: ArrayLists can be used to get a sublist of elements by using the subList() method, which returns a new ArrayList containing a portion of the original list.
Reversing: ArrayLists can be reversed by iterating through the list and swapping the positions of elements at opposite ends of the list.
Shuffle: ArrayLists can be shuffled randomly by using the Collections.shuffle() method.
Converting to an array: ArrayLists can be converted to arrays using the toArray() method, which returns an array containing all the elements of the list.
Searching: ArrayLists can be searched using the indexOf() and lastIndexOf() methods, which return the index of the first or last occurrence of a specified element in the list.
ArrayLists can be used in a variety of applications, such as implementing data structures like stacks, queues, or hash tables.
They can also be used for managing collections of data, such as in database applications or in user interfaces where lists of items need to be displayed.
For example, an ArrayList can be used to store and manage a list of customer orders in an e-commerce application. As new orders are received, they can be added to the end of the list, and completed orders can be removed from the list. The ArrayList can be sorted by order date or order status, and individual orders can be retrieved and updated as needed.
Concept of default capacity and logical capacity
In Java, an ArrayList is implemented using an array internally. When an ArrayList is created, it has a default capacity, which determines the initial size of the internal array. The default capacity of an ArrayList is 10, which means that it can initially hold 10 elements.
The default capacity is important because it determines the amount of memory that is allocated for the ArrayList when it is created. If the initial capacity is too small, the ArrayList may need to be resized frequently as elements are added or removed, which can impact performance. On the other hand, if the initial capacity is too large, it can result in wasted memory.
In addition to the default capacity, an ArrayList also has a logical capacity, which is the number of elements that are currently stored in the ArrayList. As elements are added to the ArrayList, the logical capacity increases, and as elements are removed, the logical capacity decreases.
When the logical capacity of an ArrayList exceeds its default capacity, the ArrayList automatically resizes itself by creating a new, larger array and copying the elements from the old array to the new one. This resizing process is transparent to the programmer and happens automatically behind the scenes.
It is also possible to set the initial capacity of an ArrayList explicitly using the ArrayList constructor that takes an integer parameter. This can be useful if you know the approximate size of the ArrayList ahead of time and want to avoid unnecessary resizing.
In summary, the default capacity of an ArrayList in Java is the initial size of the internal array, which is 10 by default. The logical capacity is the number of elements currently stored in the ArrayList. As elements are added or removed, the logical capacity can change, and the ArrayList may need to be resized to accommodate the changes.
To learn more about ArrayLists in Java, here's a useful article from Oracle's Java documentation: https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html
Time and Space Complexity chart, questions for engineering interviews, best practices to keep in mind when coding ArrayLists.
Here's a time and space complexity chart for common operations on ArrayLists:
*Amortized time complexity
Note that the time and space complexities can vary depending on the specific implementation of ArrayLists and the details of the operation being performed.
In general, ArrayLists have good time complexity for random access and adding or removing elements from the end of the list.
However, they have poor time complexity for inserting or removing elements from the middle of the list due to the need to shift subsequent elements. The space complexity of ArrayLists is generally good, as they only require enough memory to store the elements and some additional overhead for managing the internal array.
Here are some questions related to ArrayLists that could be asked in engineering interviews:
What is an ArrayList in Java, and how is it different from a regular array?
How do you create an ArrayList in Java, and what is the default capacity?
What are some common operations that can be performed on an ArrayList in Java?
How do you add or remove elements from an ArrayList, and what is the time complexity of these operations?
How do you iterate over the elements in an ArrayList, and what is the most efficient way to do this?
What is the difference between an ArrayList and a LinkedList, and when would you choose one over the other?
How do you sort elements in an ArrayList, and what is the time complexity of this operation?
How do you search for an element in an ArrayList, and what is the time complexity of this operation?
How do you ensure thread safety when working with an ArrayList in a concurrent environment?
What are some best practices for working with ArrayLists in Java?
These questions can help assess a candidate's understanding of the ArrayList data structure, its operations, and its use cases in engineering applications.
What is the difference between an ArrayList and a Vector in Java, and when would you choose one over the other?
Both ArrayLists and Vectors are dynamic data structures in Java that can resize themselves as needed. The main difference between the two is that Vectors are synchronised, which means that they are thread-safe and can be accessed by multiple threads simultaneously. In contrast, ArrayLists are not synchronised and are not thread-safe.
Because of their synchronisation, Vectors may be slower than ArrayLists for single-threaded applications. However, they are useful in multi-threaded environments where thread safety is important. In general, if you are working in a multi-threaded environment, it is recommended to use Vectors. If you are working in a single-threaded environment, ArrayLists may be a better choice due to their performance benefits.
It is important to note that Vector is considered a legacy class in Java, and ArrayList is the preferred choice for most use cases. However, there may still be situations where Vector is useful, such as in legacy code or in applications where thread safety is a critical concern.
In summary, the main difference between ArrayLists and Vectors is that Vectors are synchronised and thread-safe, while ArrayLists are not. The choice between the two depends on the specific needs of the application, such as whether thread safety is a concern or not.
Here are some best practices to keep in mind when coding ArrayLists:
Use the appropriate data structure: While ArrayLists are a flexible and efficient data structure, they may not always be the best choice for a given problem. Consider the requirements of the problem and the expected usage patterns before choosing an ArrayList.
Initialize with an appropriate capacity: When creating an ArrayList, it can be helpful to specify an initial capacity that is appropriate for the expected number of elements in the list. This can help to avoid frequent resizing and improve performance.
Use generics: When creating an ArrayList, use generics to ensure type safety and reduce the risk of runtime errors. This can also make the code easier to read and maintain.
Minimize the number of resizes: Resizing an ArrayList can be an expensive operation, so it's best to avoid resizing as much as possible. When creating an ArrayList, specify an appropriate initial capacity based on the expected number of elements. You can also use the ensureCapacity() method to increase the capacity of the ArrayList if necessary.
Use the appropriate method for the task: The ArrayList class provides a variety of methods for performing operations on the list. Use the appropriate method for the task at hand to ensure efficiency and correctness.
Avoid unnecessary iterations: Avoid unnecessary iterations through the ArrayList by using the appropriate method for the task. For example, use the contains() method to check if an element is in the list rather than iterating through the list manually.
Be aware of the time and space complexity: Be aware of the time and space complexity of operations on ArrayLists, and choose the appropriate operation for the task at hand to ensure efficient code.
References, for those who wish to read further on the topic:
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Time for a joke?
Why did the ArrayList go to therapy?
Because it had too many issues to index!
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