In this course, we'll learn the Collection framework and the Map Interface.
- Collection Framework vs Array
- Hierarchy of Collection Framework
- List interface - ArrayList Class
- Iterator Interface
- Set Interface
- Queue and Dequeue Interfaces
- Map Interface
- Anyone looking to get Oracle Java Certification
- Those who want to learn the Java Programming language from scratch
- Java developers who want to increase their knowledge
- Beginners with no previous coding experience in Java programming
- Those who want to learn tips and tricks in Oracle Certified Associate – Java SE 8 Programmer certification exams
- No prior knowledge is required about the Java programming language
- Basic computer knowledge
Hi there. In this video, we will discuss the conversion between Array and ArrayList. The first one is the conversion from a List to an Array. To do this, we use the toArray() method. There are two types of toArray() method. One is without parameter and the other is with parameter. It takes an Array as a parameter. For example, myList represents our ArrayList and the myArray represents our Array. So, to convert the ArrayList to Array, we just use the myList.toArray() method or you can create a new Array, and you can pass this Array as a parameter to the toArray() method. Okay, the other conversion is from an Array to a List. To do this, we use the asList() method of the Array class or the addAll() method of the Collections class. The asList() method takes an Array as a parameter, but the addAll() method takes two parameters. The first one is the name of the list and the other is the name of the Array. Okay, if you're ready, let's get some practice.
First, I will create a new class. So, I right click on the 'collectionsexample' package and select the new class options. The class name can be ConversionsLists Array, and check the check box for the main method and click the 'Finish' button. First, I will convert the ArrayList to an Array. Okay, let's create an ArrayList. List < string > list1 = new ArrayList<>(). Now, let's add some elements to this list. List1.add("Ferrari"), List1.add("Mercedes"), List1.add("BMW"), List1.add("Ford"). Okay, now let's convert this list to an Array. First, I'll use the toArray() method without parameters. I write List1.toArray. As you can see, this method returns the object Array. So, we have to assign the new Array to an Array. At the beginning of the code I write, objectArray1=.
Okay, the conversion is ready. Let's print the elements of the List and Array. S.out.printIn(list1), and S.out.printIn(Arrays.toString(array1)). Let's run and see. As you can see, the elements of the List and Array are printed on the console. So, the conversion is successful. Now, let's use the toArray() method with parameter. First, I'll convert this line to the comment line. Okay, now I will create an Array, String Array1= new String. So, we have to write the size of this Array. You can write the size of the list or you can only put a zero. But the point you need to pay attention to is this; the size you write here must not be larger than the size of the list, otherwise non-correlated elements are converted to null. For example, currently, the size of this list is four. If we type five here, the fifth element will be printed as null. But if you write zero, one, two, three or four here, the output will be the same, but the correct usage is to write the size of the list.
So, list1.size. Okay, now let's continue. In the next line, I write, Array1=list1.toArray(Array1). The conversion is ready. Let's run the code and test it. As you can see, the output is the same. Also, you can write it in one line. Inside the parentheses, you can use the new keyword. So, I'll convert this line to the comment line and I'll copy the part after the equal sign and paste it inside the parentheses. Okay, this will be a string Array. Okay, so this is also valid. You can use this syntax. Now let's run and see. As you can see, the output is the same. Also, other than the ready made method, you can convert it with the for or for-each loop, let's use the for loop. First, I'll copy this line and paste it here. So we need to create an Array and I will convert this line to the comment line again. Let's create the for loop, for(int i=0). The condition is, i< list1.size and i ++. In the for loop, I write, Array 1[i] and after the equal sign, I write, list1.get.
So, thanks to the get() method, we can get the elements of a list which is the specific index. So, in parentheses I write i. 'i' represents the index of the list and Array. In each loop, the elements of the list will assign to the Array respectively. So, let's run and see. As you can see, the output is ready. Also, after the conversion, you can add many more elements to the list, but we cannot add an element to the Array because the size of the Array is fixed, not changed. For example, let's add the fifth element to the list; list.add("Opel"). Let's run it one more time. As you can see, the new element is added to the list. Yes, the conversion from the List to an Array is like this. Now, let's look at the conversion from the Array to a List. Let's create an animals Array; String animalsArray= new String, and inside the curly braces, I'll create the elements.
The first element can be "Dog", the second can be "Cat", and third can be "Cow", and the last element can be "Lion". Okay, the Array is ready. Also, you can create the Array just by typing the curly braces. Now, let's convert this Array to an ArrayList. First, I will use the asList() method of the Arrays class. So I write, list < String > animalsList= Arrays.asList. As the parameter, l'll write the Array name, ie., animalsArray. Now, let's print the elements of the Array and ArrayList; S.out.printIn Arrays.toString(animalsArray), and S.out.printIn(animalsList). Let's run and see. As you can see, the conversion is successful. Also, if you use the ArrayList instead of the List, this time you should assign the Arrays.toArray() method as the constructor parameter of the ArraysList. Let's change it. I'll copy and paste this line.
I'll convert this line to the comment line. This will be ArrayList, and after the equal sign, I write new ArrayList, and in parentheses I write Arrays.asList(animalArray). So, this usage is also valid. Now, I will convert this line to the comment line. Now, let's use the addAll () method of the Collections class. First, I will create an ArrayList. ArrayList < string > animalsList= new ArrayList<>(). And in the next line I write, Collections.addAll. The addAll() method takes two parameters. The first one is the name of the list, so the animalsList, and the second parameter is the name of the Array, so the animalsArray. Okay, let's run and see. As you can see, the output is the same. Also, we can convert it using the for or for-each loop. If you want this time, let's use the for-each loop. First, I will convert this line to the comment line.
And let's create the for-each loop, for(String animal : animalsArray). And in the loop, I write animalsList.add (animal). Thus, in each iteration, the elements of the Array will be added to the ArrayList. Let's run and see. As you can see, the output is the same. Also, you can add an element to the ArrayList after the conversion. Let's add another animal to the list, animalsList.add("Monkey"). Let's run and see. As you can see, the monkey is added to the list, but here is a small detail you need to pay attention to. If you do the conversion using the asList() method, you can no longer add an element to the list because these will now be linked Arrays and you can't add elements since the Arrays are fixed in size. Let's just do an example. First of all, let's convert the for loop here to a comment line. Let's also activate the asList() method and I will also add the comment on this line. Yes, let's run the application now.
And as you can see, we are getting the unsupported operation exception error because we have done the conversion using the asList method and adding a new element is no longer allowed. So, what happens if we change any element? For example, let's change the first element to Rabbit. AnimalsArray=''Rabbit''. And let's run the code and observe the output. As you can see, the first element of the Array and ArrayList has changed. The reverse is also true. So, if you change an element of the ArrayList, both will be changed. For example, let's change it to animalsList.set. The Parameters will be zero and "Rabbit". Yes, let's run and test it one more time. As you can see, both have changed. As a result, if you do the conversion using the asList() method, you can no longer add elements to the Array or delete any element of the Array. If you change an element, this time the change is applied to both. Do not forget this. Yes, let's take a short break here. See you in the next lesson.
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