To create an ArrayList in Java, you need to import the java.util.ArrayList class, declare and initialize it and use add, get, set, remove and other methods to operate elements. 1. Import class: import java.util.ArrayList; 2. Declaration initialization: ArrayList
Creating an ArrayList in Java is very simple. It belongs to Java Collections Framework. Before using it, you need to introduce the ArrayList class in the java.util package.
Import the ArrayList class
Before using ArrayList, you need to import it first:
import java.util.ArrayList;
If you are using an IDE (such as IntelliJ or Eclipse), you will automatically add this sentence after entering ArrayList . However, it is no problem to add it manually, and it will not affect the program operation.
Declare and initialize an ArrayList
The basic format for declaring and initializing ArrayList is as follows:
ArrayList<DataType> listName = new ArrayList<>();
Among them, DataType is the data type you want to store, such as String , Integer , custom classes, etc. For example:
ArrayList<String> names = new ArrayList<>(); ArrayList<Integer> numbers = new ArrayList<>();
Note: ArrayList can only store object types and cannot directly store basic data types (such as int, double). But Java provides automatic boxing, so you can add numbers directly like above.
Add elements to ArrayList
After creating an ArrayList, you can use the .add() method to add elements to it:
names.add("Alice");
names.add("Bob");
numbers.add(10);
numbers.add(20);You can also specify the location to insert elements:
names.add(1, "Charlie"); // Insert Charlie at index 1
- If no position is specified, the element will be added at the end.
- If the inserted position exceeds the current length, an exception will be thrown.
Get and manipulate elements in ArrayList
To access an element, use .get(index) method:
System.out.println(names.get(0)); // Output Alice
To modify the value of a certain position, you can use .set(index, value) :
names.set(0, "David"); // Change the value of index 0 to David
To delete elements, you can use .remove(index) or directly pass the object:
names.remove(0); // Delete the element with index 0 names.remove("Charlie"); // Delete the element with value CharlieView the size of the ArrayList
To get how many elements are in the current ArrayList, use .size() method:
System.out.println(names.size()); // Output the current quantity
Basically that's it. After mastering these basic operations, you can flexibly use ArrayList to handle dynamic arrays. It is often used to replace ordinary arrays in actual development because it can automatically expand and is more convenient to use.
The above is the detailed content of how to create an arraylist in java. For more information, please follow other related articles on the PHP Chinese website!
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