ArrayLists and arrays

Arrays and ArrayLists are examples of structured data types: they can store multiple elements in order, and the elements can be accessed by their indices. Earlier in the course we encountered Strings. A String is similar in that it contains multiple elements (the characters) and they can be accessed by their indices (using the charAt method). However, unlike Strings, arrays and ArrayLists are mutable, that is, their contents can be modified after construction.

Here is a brief comparison of some of the features of arrays and `ArrayList`s.

ArrayLists

Created using the new operator. The type of data it holds goes in the angle brackets. Example:
```
     ArrayList<String> list = new ArrayList<String>();
    
```
An ArrayList can be created to hold any type of Java object (but not primitive types; we have to use the wrapper classes such as Integer instead)
A newly created ArrayList has length 0.
The length of the list will expand as necessary as elements are added.
The length of the list can be obtained using the method size().
New elements are added to the end of the list using the add(element) method.
The element at index i can be accessed using the get method:
```
     String s = list.get(i);
     
```
The element at index i can be changed using the set method:
```
      list.set(i, "foo");
    
```
The ArrayList has a large number of useful methods in addition to add, get and get. Some useful ones include contains, remove, addAll, and sort. Check out the ArrayList API documentation

Arrays

Created using the new operator. The type of data it holds goes before the square brackets. Example:
```
     String[] arr = new String[5];
    
```
An array can be created to hold any type of data, including primitive types.
The length must be specified when the array is constructed. A newly created array of primitive type contains all zeros. A newly created array of objects contains all nulls.
The length can be obtained by accessing the length attribute (without parentheses).
New elements cannot be added, since the length is fixed.
The element at index i can be accessed using the bracket notation:
```
    String s = arr[i];
    
```
The element at index i can be changed using the bracket notation:
```
    arr[i] = "foo";
    
```
There are no useful methods that are part of an array type. You can, however, find some static utility methods in the Arrays class, including toString, copyOf, and sort. See the Arrays API documentation

ArrayLists and arrays

Here is a brief comparison of some of the features of arrays and ArrayLists.

ArrayLists

Arrays

Here is a brief comparison of some of the features of arrays and `ArrayList`s.