Array and ArrayList in Java | Selenium Interview Question

Recently one of my friend has gone for interview in one of the leading travel domain company where he was asked about Array and ArrayList and interviewer was keen about performance of value insertion in Array and ArrayList.

So lets begin with small introduction of Array and ArrayList.

Array is a data structure defined in core java which stores multiple data of same type (Can store Object as well) and it is of fixed size.But if you want to learn more about Array and its implementation then I would suggest you, Read Arrays in Java and its implementation in WebDriver.

Similarly ArrayList is part of Collection Framework which store similar kind of Objects and in the core of it, it use array. So if you want to learn more about ArrayList then I would suggest you to read Java Doc For ArrayList .

So up to now we understand that both stores the data of same type but one have primitive data type along with object and other only takes object. But this is not the only thing that we need to remember. There are some parameters over whichArray and ArrayList we need to analyse.

Primitive: Array can store primitive data type like int, char, double etc and objects While ArrayList can only store objects in it.

But if you want to add any primitive in ArrayList in that case it converts primitive data type to equivalent Object define in Java using Auto-boxing.

So here 1 which is int, internally get converted to Integer Object.

Size: 1- In Layman term storage capability of Array is fixed while ArrayList has dynamic storage capability.
2- In Array we define size of array at time of its initialisation while In ArrayList we never define the size at the time of its initialisation. But internally ArrayList use concepts of Array and when ever we create any ArrayList, it creates one Array of some specific size and once this size is attained, It dynamically creates array of double of initial size and copy initial data in new array that is dynamically created.


Support to Generics: 1- ArrayList is type-safe while Array is not.

2- Type-safety in Java is handled using Generics and ArrayList use generics while this can’t be used in array. If any time we try to use generics in that case it throws exception ArrayStoreException because instance of Array would not be able to convert it in to the type defined for Array.

Dimensions: Array can be defined multi-dimensional while ArrayList can be one dimensional.

Iteration: If user wants to iterate through each element of ArrayList then he/she needs to use Iterator from Java or For each loop to look into or to access each element, While it can be done through for loop and For Each loop for array.

Performance: this is one factor that takes constant time in both (Up to initial size of ArrayList) if we are calling add() and get() in ArrayList.But automatic resizing in ArrayList might cause slowness in insertion of data (Adding Data in ArrayList).

Length: Array uses length variable to find actual size or length of array but in case of ArrayList, we need to call size() function to find the length of ArrayList.

So this was the basic difference between Array and its dynamic brother ArrayList.

Hope this post will be helpful.

Happy Learning…

If you want to learn more about Java then please read Java Tutorial.



Inspecting Elements for writing XPath, CSS Selector in Chrome

The most important part in any kind of automation is, identifying various elements over which we want to perform an action and when it comes to web application or android application automation using Selenium WebDriver or Appium, we fall for Chrome, Firefox or Internet Explorer to find the right set of XPath or CSS selector. For the same, all most all of the browsers have started providing support for various developer tools and this has made our job of identifying various web elements quite easily. Before chrome browser launch, people were dependent on various add-ons and extension like Firebug to inspect and edit HTML content during their front end development.

So in this Post, We will learn to inspect element, write XPath and CSS Selector using Chrome Browser. So this post will be divided into the following steps

  • Inspecting element & Opening Devtool (Developer Tool) in the Chrome Browser
  • Highlighting Elements through XPath, CSS Selector, and ID.

Inspecting Element & Opening Developer tool in Chrome Browser
Recent Version of Chrome browser provides multiple ways to open the Chrome Developer Tool

  1. Press F12 on Keyboard
  2. Press COMMAND + Option+C (In Mac) and Press Control+Shift+C (In Windows)
  3. Select any element on page and right click on your mouse.
  4. Navigate to Home Icon at top right corner, Navigate to More Tools > Developer Tools

Highlighting HTML code of any element using the developer tool
Option 1: Select Element and Right Click and From the context menu, Select Inspect Option.
In this example, we are taking google home page and here we are keeping our cursor in the search box and performing right click and selecting Inspect.
Inspect Element in ChromeAfter Selecting the Inspect option from the context menu, It will open the element view of developer tool where it will highlight the HTML code. So as an automation engineer we need to write our XPath or CSS Selector by seeing various attributes of selected HTML code.

Inspect HTML Code in Chrome Developer ToolOption 2: Open Developer Tool using any of the above-mentioned ways and Click on Select icon on developer tool and click on an element for which we want to see the HTML code.

Inspecting Element Using Chrome Dev Tool

Now we are familiar with all the ways to highlight HTML code and we are also familiar with the ways to open Chrome Developer Tool. Now we are moving to the next stage of this post where we are going to search specific tag, id, XPath and CSS Selector.

Searching and Validating already written XPath, CSS Selector

This is a very important section Because this is going to give you a perspective to validate your locators before using it in code. These all locators are mainly used in fineElement() or findElements() method in Selenium WebDriver to identify WebElements on any of the web pages for which we are going to write the script.

Here again, we have two ways to do this.

Option 1: Using Find box (Search in HTML Code) of Developer Tool.


Recently this find box on developer tool has got a mighty hand to find HTML code using String Pattern, Xpath, and CSS Selector which earlier was not possible except searching string pattern.
So the first step that we need to perform is to open the find box on developer console. So for this user needs to press Command+F (In Mac) or Ctrl+F (In Windows) to open the find box.

Find Box in Chrome Developer Tool
String Pattern: It will contain id, the class attribute, and HTML tag.

1- So here we would be picking up HTML tag name, id and class attribute.

So let’s take input text and put it in the find box and see it will show all the input tags in the whole HTML page and as soon as you will click on enter it will increase the count and will also highlight the element on the web page which is selected in search Like this

Searching String pattern in HTML Code

Similarly, we can search any string pattern either it is id, class or any other attribute mentioned in HTML.

XPath and CSS Selector in Find Box: Correct element gets highlighted in element tab if correct XPath and CSS Selector are inserted in Find Box. This way we can validate our XPath and CSS Selector and this way we could decide whether findElement() or findElements() Method need to be invoked in code.

So here is the XPath and CSS Selector of Search textbox on Google Home page.

XPath: //input[@name=’q’]

CSS Selector: input[name=q]

So if you are wondering how to write effective XPath and CSS Selector then read these articles

XPath in Selenium

Absolute XPath in Selenium WebDriver

Xpath in Selenium :: Contains() and starts-with() function in XPath

CSS Selector in Selenium WebDriver

Validating CSS Selector:  As soon CSS Selector would be inserted in find box, it will highlight the code as well as the element on the web page like thisXP

Above visual also shows that total 1 of 1 element has been found in HTML, it means above CSS Selector is unique and returning only one element. So the user should use findElement() method in their code. But if above CSS Selector has shown 1 of (a number greater than one) it shows that CSS Selector is not unique and if the user wants to use this locator in the code, he/she needs to use findElements() method which deals with the list of element in Selenium WebDriver.


Validating XPath: Similarly, we will insert XPath in the find box and will see the above result because equivalent XPath has been written for the search text box.Validating Xpath in Chrome Developer Tool

Option 2: Using the Console of Chrome Developer Tool

This is the second way of validating XPath and CSS Selector written to use in the script. So here the user has two options to open the console.

1- Just by pressing [ESC] on the keyboard and it will open the console at the bottom


2- User can directly click on the console tab of the developer tool. (Probably it will be visible in above image just beside Elements tab)

So once console appear user need to follow the following pattern to validate XPath and CSS Selector

For XPath:  User can use following string in the console
$x(“Xpath”) and hit enter. Since XPath for search box is //input[@name=’q’]

So the final string which needs to be inserted is

Above will return an array and element at 0 indexes is the element that we want to validate( Now use need to validate the size of the array returned and if size is one it means the element is uniquely identified.)
XPath in Console of Chrome Developer Tool

For CSS Selector: user needs to follow this pattern in the console to validate it.

$$(“CSS Selector”).

So enter the following string in the console.

This will also return an array and if the array size is zero means element has been uniquely identified.

Hope you like this article and if like then share it with your friends as well.




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