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Learn Java: ArrayLists
Creating ArrayLists
To create an ArrayList
, we need to declare the type of objects it will hold, just as we do with arrays:
ArrayList<String> babyNames;
We use angle brackets <
and >
to declare the type of the ArrayList
. These symbols are used for generics. Generics are a Java construct that allows us to define classes and objects as parameters of an ArrayList
. For this reason, we can’t use primitive types in an ArrayList
:
// This code won't compile: ArrayList<int> ages; // This code will compile: ArrayList<Integer> ages;
The <Integer>
generic has to be used in an ArrayList
instead. You can also use <Double>
and <Char>
for types you would normally declare as double
s or char
s.
We can initialize to an empty ArrayList
using the new
keyword:
// Declaring: ArrayList<Integer> ages; // Initializing: ages = new ArrayList<Integer>(); // Declaring and initializing in one line: ArrayList<String> babyNames = new ArrayList<String>();
Instructions
1.
Import the ArrayList
package from java.util
.
2.
Create a new ArrayList
that will contain String
elements and call it toDoList
.