What is ArrayList its type in Java?

What is ArrayList its type in Java?

I'd be happy to explain!

ArrayList is a class in the Java programming language that provides resizable-array-based implementations of List and Collection interfaces, which are part of the Java Collections Framework (JCF). It is a widely used and highly efficient data structure that allows you to store multiple elements of the same type in a single variable.

The ArrayList class is defined in the java.util package and has several key features:

Now, let's talk about the type of an ArrayList:

In Java, an ArrayList is a class, not a primitive type like int or boolean. Specifically, it is a subclass of AbstractList and implements the List interface. This means you can use an ArrayList where any other list-type data structure would be accepted (e.g., in a method that takes a List as a parameter).

When declaring an ArrayList variable, you need to specify its type, which indicates the type of elements it will store. For example:

ArrayList myStringList = new ArrayList<>();
ArrayList myIntList = new ArrayList<>();

In these examples, myStringList and myIntList are instances of ArrayList, with the types String and Integer, respectively. This allows you to store only strings or integers in those lists, respectively.

The type parameter (in this case, String and Integer) is used when you create a new instance of the ArrayList using its constructor:

String[] array = {"Hello", "World!"};
ArrayList myStringList = new ArrayList<>(Arrays.asList(array));

In summary, an ArrayList in Java is a class that provides dynamic storage for elements of the same type. You can specify the type of elements it will store when declaring its variable, and it offers efficient methods for inserting, removing, or searching elements.

I hope this explanation helps! Let me know if you have any further questions.

What is polymorphic in Java?

I'm happy to respond in English this time!

In Java, polymorphism refers to the ability of an object to take on multiple forms. The term "polymorphism" comes from the Greek words "poly," meaning many, and "morph," meaning form.

There are several ways that polymorphism can be achieved in Java:

Example:

public class Calculator {
public int calculate(int x) { return x; }
public double calculate(double x) { return x; }
public String calculate(String s) { return s; }
public static void main(String[] args) {
Calculator calculator = new Calculator();
System.out.println(calculator.calculate(5)); // prints 5
System.out.println(calculator.calculate(3.14)); // prints 3.14
System.out.println(calculator.calculate("hello")); // prints hello
}
}

Example:

public class Animal {
public void sound() { System.out.println("The animal makes a sound."); }
}
public class Dog extends Animal {
@Override
public void sound() { System.out.println("The dog barks!"); }
}
public static void main(String[] args) {
Animal myAnimal = new Animal();
myAnimal.sound(); // prints "The animal makes a sound."
myAnimal = new Dog();
myAnimal.sound(); // prints "The dog barks!"
}

Example:

public class Vector2D {
public int x;
public int y;
public Vector2D(int x, int y) { this.x = x; this.y = y; }
@Override
public String toString() { return "(" + x + ", " + y + ")"; }
public static Vector2D add(Vector2D v1, Vector2D v2) {
return new Vector2D(v1.x + v2.x, v1.y + v2.y);
}
}
public class Main {
public static void main(String[] args) {
Vector2D v1 = new Vector2D(2, 3);
Vector2D v2 = new Vector2D(4, 5);
Vector2D sum = Vector2D.add(v1, v2);
System.out.println(sum); // prints (6, 8)
}
}

In each of these cases, the object is taking on multiple forms or behaviors, which is the essence of polymorphism.

I hope this explanation helps!