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Introduction to Java ArrayList
Overview:
The ArrayList class in Java is part of the java.util package and provides a resizable-array implementation of the List interface. It is widely used due to its dynamic size, ease of use, and ability to store duplicate elements.
Creating an ArrayList
Example:
To create an ArrayList, you need to instantiate it using the ArrayList class. Here is a simple example:
import java.util.ArrayList;
class Example1 {
public static void main(String[] args) {
ArrayList names = new ArrayList();
names.add("Alice");
names.add("Bob");
System.out.println(names);
}
}
Console Output:
[Alice, Bob]
Adding Elements
Example:
Elements can be added to an ArrayList using the add() method. This method appends the specified element to the end of the list.
import java.util.ArrayList;
class Example2 {
public static void main(String[] args) {
ArrayList numbers = new ArrayList();
numbers.add(10);
numbers.add(20);
numbers.add(30);
System.out.println(numbers);
}
}
Console Output:
[10, 20, 30]
Accessing Elements
Example:
You can access elements in an ArrayList using the get() method. This method takes an index as an argument and returns the element at that position.
import java.util.ArrayList;
class Example3 {
public static void main(String[] args) {
ArrayList fruits = new ArrayList();
fruits.add("Apple");
fruits.add("Banana");
System.out.println(fruits.get(1));
}
}
Console Output:
Banana
Modifying Elements
Example:
The set() method allows you to modify an element at a specific index. It takes two arguments: the index of the element to replace and the element to be stored.
import java.util.ArrayList;
class Example4 {
public static void main(String[] args) {
ArrayList cars = new ArrayList();
cars.add("Toyota");
cars.add("Honda");
cars.set(1, "Ford");
System.out.println(cars);
}
}
Console Output:
[Toyota, Ford]
Removing Elements
Example:
Elements can be removed from an ArrayList using the remove() method. This method can take either the index of the element to be removed or the element itself.
import java.util.ArrayList;
class Example5 {
public static void main(String[] args) {
ArrayList animals = new ArrayList();
animals.add("Dog");
animals.add("Cat");
animals.remove("Dog");
System.out.println(animals);
}
}
Console Output:
[Cat]
Iterating Over an ArrayList
Example:
You can iterate over an ArrayList using a for-each loop. This loop simplifies the iteration process and makes the code more readable.
import java.util.ArrayList;
class Example6 {
public static void main(String[] args) {
ArrayList colors = new ArrayList();
colors.add("Red");
colors.add("Green");
colors.add("Blue");
for (String color : colors) {
System.out.println(color);
}
}
}
Console Output:
Red
Green
Blue
Checking if an ArrayList Contains an Element
Example:
The contains() method checks if an ArrayList contains a specific element. It returns true if the element is found, otherwise false.
import java.util.ArrayList;
class Example7 {
public static void main(String[] args) {
ArrayList cities = new ArrayList();
cities.add("New York");
cities.add("Los Angeles");
System.out.println(cities.contains("New York"));
}
}
Console Output:
true
Getting the Size of an ArrayList
Example:
To determine the number of elements in an ArrayList, use the size() method. This method returns an integer representing the number of elements.
import java.util.ArrayList;
class Example8 {
public static void main(String[] args) {
ArrayList books = new ArrayList();
books.add("1984");
books.add("Animal Farm");
System.out.println(books.size());
}
}
Console Output:
2
Clearing an ArrayList
Example:
The clear() method removes all elements from an ArrayList, leaving it empty.
import java.util.ArrayList;
class Example9 {
public static void main(String[] args) {
ArrayList languages = new ArrayList();
languages.add("Java");
languages.add("Python");
languages.clear();
System.out.println(languages);
}
}
Console Output:
[]
