How can I add a name (String) within a predefined array in java?

It is not possible to add an element to an array that is already full. If you have a 3-position arrangement, you can not modify it later. You can replace the name of a position with another name, but do not add more. I can think of two options to solve your problem.

Option 1: Create an arrangement with one more position to save the name of the fruit received by the keyboard in the last one.

import java.util.Scanner;

public class Ejemplo {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        // Arreglo con 1 dimension más para el String solicitado
        String[] frutas = new String[4];
        frutas[0] = "manzana";
        frutas[1] = "naranja";
        frutas[2] = "melon";

        // Variable para guardar el nombre de la fruta ingresada
        String nuevaFruta;

        // Pedir el nombre de una fruta por teclado
        System.out.println("Ingrese el nombre de una fruta: ");
        nuevaFruta = scanner.nextLine();

        // Cerrar Scanner
        scanner.close();

        // Guardar el nombre de la nueva fruta en la última posición del arreglo
        frutas[3] = nuevaFruta;

        // Imprimir arreglo
        for (String nombre : frutas) {
            System.out.println(nombre);
        }
    }
}

Option 2: Use ArrayList , its advantage is that the number of elements it stores, it does so dynamically, that is, it is not necessary to declare its size as it happens with the Arrays .

import java.util.ArrayList;
import java.util.Scanner;

public class Ejemplo {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        // ArrayList de tipo String
        ArrayList<String> frutas = new ArrayList<>();

        // Arregar frutas al ArrayList
        frutas.add("manzana");
        frutas.add("naranja");
        frutas.add("melon");

        // Pedir el nombre de una fruta por teclado
        System.out.println("Ingrese el nombre de una fruta: ");

        // Guardar el nombre de la fruta en el ArrayList
        frutas.add(scanner.nextLine());

        // Cerrar Scanner
        scanner.close();

        // Imprimir arreglo
        for (String nombre : frutas) {
            System.out.println(nombre);
        }
    }
}

I hope I have helped you.

Arrays in java are not resizable, so it is not possible to add one more position to the frutas array, since its definition restricts its size to 3 elements.

If the requirements of your application indicate that the user should be allowed to add elements to the collection indefinitely, I recommend that you use a list-type data structure, for example ArrayList .