Why do we use ArrayList instead of Array in Java?

Why do we use ArrayList instead of Array in Java?

Java ArrayList

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Java ArrayList

The ArrayList class is a resizable array, which can be found in the java.util package.

The difference between a built-in array and an ArrayList in Java, is that the size of an array cannot be modified (if you want to
add or remove elements to/from an array, you have to create a new one). While elements can be added and removed from an ArrayList whenever you want. The syntax is also slightly different:

Example

Create an ArrayList object called cars that will store strings:

import java.util.ArrayList; // import the ArrayList class

ArrayList cars = new ArrayList(); // Create an ArrayList object

If you don’t know what a package is, read our Java Packages Tutorial.


Add Items

The ArrayList class has many useful methods. For example, to add elements to the ArrayList, use the add() method:

Example

import java.util.ArrayList;

public class Main {
public static void main(String[] args) {
ArrayList cars = new ArrayList();
cars.add(“Volvo”);
cars.add(“BMW”);
cars.add(“Ford”);
cars.add(“Mazda”);
System.out.println(cars);
}
}

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Access an Item

To access an element in the ArrayList, use the get() method and refer to the index number:

Example

cars.get(0);

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Remember: Array indexes start with 0: [0] is the first element. [1] is the second
element, etc.



Change an Item

To modify an element, use the set() method
and refer to the index number:

Example

cars.set(0, “Opel”);

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Remove an Item

To remove an element, use the remove() method
and refer to the index number:

Example

cars.remove(0);

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To remove all the elements in the ArrayList, use the clear() method:

Example

cars.clear();

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ArrayList Size

To find out how many elements an ArrayList have, use the size method:

Example

cars.size();

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Loop Through an ArrayList

Loop through the elements of an ArrayList with a for loop, and use the
size() method to specify how many times the loop should run:

Example

public class Main {
public static void main(String[] args) {
ArrayList cars = new ArrayList();
cars.add(“Volvo”);
cars.add(“BMW”);
cars.add(“Ford”);
cars.add(“Mazda”);
for (int i = 0; i

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You can also loop through an ArrayList with the for-each loop:

Example

public class Main {
public static void main(String[] args) {
ArrayList cars = new ArrayList();
cars.add(“Volvo”);
cars.add(“BMW”);
cars.add(“Ford”);
cars.add(“Mazda”);
for (String i : cars) {
System.out.println(i);
}
}
}

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Other Types

Elements in an ArrayList are actually objects. In the examples above, we created elements
(objects) of type “String”. Remember that a String in Java is an object (not a primitive type). To use other types, such as int, you must specify an equivalent wrapper class: Integer. For other primitive types,
use: Boolean for boolean, Character for char, Double for double,
etc:

Example

Create an ArrayList to store numbers (add elements of type Integer):

import java.util.ArrayList;

public class Main {
public static void main(String[] args) {
ArrayList myNumbers = new ArrayList();
myNumbers.add(10);
myNumbers.add(15);
myNumbers.add(20);
myNumbers.add(25);
for (int i : myNumbers) {
System.out.println(i);
}
}
}

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Sort an ArrayList

Another useful class in the java.util package is the Collections class, which include the sort() method for sorting lists
alphabetically or numerically:

Example

Sort an ArrayList of Strings:

import java.util.ArrayList;
import java.util.Collections; // Import the Collections class

public class Main {
public static void main(String[] args) {
ArrayList cars = new ArrayList();
cars.add(“Volvo”);
cars.add(“BMW”);
cars.add(“Ford”);
cars.add(“Mazda”);
Collections.sort(cars); // Sort cars
for (String i : cars) {
System.out.println(i);
}
}
}

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Example

Sort an ArrayList of Integers:

import java.util.ArrayList;
import java.util.Collections; // Import the Collections class

public class Main {
public static void main(String[] args) {
ArrayList myNumbers = new ArrayList();
myNumbers.add(33);
myNumbers.add(15);
myNumbers.add(20);
myNumbers.add(34);
myNumbers.add(8);
myNumbers.add(12);

Collections.sort(myNumbers); // Sort myNumbers

for (int i : myNumbers) {
System.out.println(i);
}
}
}

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