Array and ArrayList

A tale of friendship, heartache and redemption

-

What we’ll cover

Differences Between Array and Arraylist

Similarities Between Array and Arraylist

Difference Between Array and Arraylist In Java

Common Array and Arraylist Tasks

-

Differences between Array and ArrayList

-

Resizable

• Array is static in size. Also known as a fixed length data structure.
  • One can not change the length after creating the Array object.
• ArrayList is dynamic in size.
  • Each ArrayList object has instance variable capacity which indicates the size of the ArrayList.
  • As elements are added to an ArrayList its capacity grows automatically.

-

Performance

• Performance of Array and ArrayList depends on the operation you are performing

-

Performance

• Resize() operation : Automatic resize of ArrayList will slow down the performance as it will use temporary array to copy elements from the old array to new array.

-

Performance

add() or get() operation : adding an element or retrieving an element from the Array or ArrayList object has almost same performance

-

Primitives

• One misconception is that we can store primitives (int, float, double) in ArrayList, but it is not true

-

Primitives

• ArrayList can only contain non-primitve data types (like Integer, Float, Double)
• ArrayList can not contain primitive data types (like int, float, double)
• Array can contain both primitive as well as non-primitive (Objects) data types.

-

Primitives

• Suppose we have ArrayList object,

ArrayList<Integer>  arraylistobject = new ArrayList();
arraylistobject.add(23);  // try to add 23 (primitive)

-

ArrayList Autoboxing

JVM through Autoboxing (converting primitives to equivalent objects internally) ensures that only objects are added to the arraylistobject. thus , above step internally works like this :

arraylistobject.add(new Integer(23));      
// Converted int primitive to Integer object and added to arraylistobject  

-

Length

• The number of elements in an ArrayList is provided by the size() method
• The number of elements in an array is provided by the length variable.

for example:

Integer arrayobject[] = new Integer[3];
arraylength= arrayobject.length; //uses arrayobject length variable

ArrayList<Integer>  arraylistobject = new ArrayList();
arraylistobject.add(12);
arraylistobject.size(); //uses arraylistobject size method

-

Adding elements

• We can insert elements into the arraylistobject using the add() method.
• We can insert elements into the array using the assignment operator.

for example:

Integer addarrayobject[] = new Integer[3];
addarrayobject[0]=new Integer(8); //new object is added to the array object

ArrayList<Integer>  arraylistobject = new ArrayList();
arraylistobject.add(12);

-

Multi-dimensional

• Array can be multi-dimensional, while ArrayList is always single dimensional.

for example:

Integer addarrayobject[][] = new Integer[3][2];
addarrayobject[0][0]= new Integer(8);

-

Similarities Between Array and ArrayList

-

1. add and get method: Performance of Array and ArrayList are similar for the add and get operations.
2. Duplicate elements: Both Array and ArrayList can contain duplicate elements.
   • Unlike Sets and Maps (no duplicate keys)
3. Null Values: Both can store null values and uses index to refer to their elements.
4. Ordered: Both guarantee ordered elements.
   • Unlike HashMap and HashSet

-

Difference between Array and ArrayList in Java

-

	Array	ArrayList
Resizable	No	Yes
Primitives	Yes	No
Iterating values	for, for each	Iterator,for each
Length	length variable	size method
Performance	Fast	Slow in comparision
Multidimensional	Yes	No
Add Elements	Assignment operator	add method

-

Common Array and Arraylist Tasks

-

Declaration and Instantiation

Array:

String[] villains = new String[5];

ArrayList:

ArrayList<String> heroes = new ArrayList<String>();

-

Add Items

Array:

villians[0] = "Dark Pheonix";
villians[1] = "Deadshod";
villians[2] = "CatWoman";
villians[3] = "Green Goblin";
villians[4] = "Poison Ivy";

ArrayList:

heros.add("Hellboy");
heros.add("Storm");
heros.add("Spawn");
heros.add("Silver Surfer");
heros.add("Mr. Fantastic");

-

Access an Item

Array:

villians[3];

ArrayList:

heroes.get(3);

-

Change an Item

Array:

vilians[4] = "Apocalypse";

ArrayList:

heroes.set(4, "The Tick");

-

Remove an Item

Array:

• There is no way to remove and item from an array.
• You will need to duplicate values into a new array sans the value to remove.

ArrayList:

heroes.remove(0);

-

Clear an Item

Array:

• There is no way to clear an array.
• You will need to create a new array

ArrayList:

heroes.clear();

-

Length of Items

Array:

villians.length;

ArrayList:

heroes.size();