ArrayList Vs Array

Array is fixed length data structure while ArrayList is a variable length. Array Length cannot be changed once it create, Array List will re-size itself depending on capacity and load factor.
To calculate Array has length variable and ArrayList has size() method.
ArrayList Cannot store Primitives, it will hold only objects. If it holds any primitives, through autoboxing it will convert primitives to Objects.
For Insertion ArrayList have add() method and for Array we can use assignment operator to store element into array.
e.g Array
    Object[] objectArray=new Object[5];
    objectArray[2]=new Object();

We can create instance of ArrayList without specifying the size, but its mandatory to provide size of Array while creating it.