Comparable Interface in Java Error

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Comparable Interface in Java Error

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I have a problem with understanding the interface Comparable .

The application by console consists of printing the respective objects and comparing which is the most expensive and cheapest product. The problem is that I do not understand how to apply it to my application so that it prints by the method toString() :

Most expensive product:
Cheapest product:

This is the functional code of the application:

Product:

package ar.com.minisuper.sistema;

public abstract class Producto implements Comparable<Producto> {
    protected String nombre;
    protected int precio;

    public Producto(String nombre,  int precio) {
        this.nombre  = nombre;
        this.precio = precio;   
    }

    public String getNombre() {
        return nombre;
    }

    public void setNombre(String nombre) {
        this.nombre = nombre;
    }

    public double getPrecio() {
        return precio;
    }

    public void setPrecio(int precio) {
        this.precio = precio;
    }

    @Override
    public int compareTo(Producto o) {
        return this.getPrecio()>o.getPrecio()?1:this.getPrecio()<o.getPrecio()?-1:0;
    }
}

Drink:

package ar.com.minisuper.sistema;

public class Bebida extends Producto {
    private double unidadVenta;

    public Bebida(String nombre, double unidadVenta, int precio) {
        super(nombre, precio);
        this.unidadVenta = unidadVenta;
    }

    @Override
    public String toString() {
        return "Nombre: " + this.nombre + " /// " + "Litros: " + this.unidadVenta + " /// " + "Precio: $" + this.precio;
    }
}

Shampoo:

package ar.com.minisuper.sistema;

public class Shampoo extends Producto {
    private int unidadVenta;

    public Shampoo( String nombre, int unidadVenta, int precio ) {
        super(nombre, precio);
        this.unidadVenta = unidadVenta;
    }

    @Override
    public String toString() {
        return "Nombre: " + this.nombre + " /// " + "Contenido: " + this.unidadVenta + "ml" + " /// " + "Precio: $" + this.precio;
    }
}

Fruit:

package ar.com.minisuper.sistema;

public class Fruta extends Producto {
    private String unidadVenta;

    public Fruta(String nombre, int precio, String unidadVenta) {
        super(nombre, precio);
        this.unidadVenta = unidadVenta;
    }

    @Override
    public String toString() {
        return "Nombre: " + this.nombre + " /// " + "Precio: $" + this.precio + " /// " + "Unidad de venta: " + this.unidadVenta;
    }
}

And the main:

package ar.com.minisuper.sistema;

public class Main {

    public static void main(String[] args) {
        Bebida colaZero = new Bebida( "Coca-Cola Zero", 1.5, 20 );
        Bebida cola = new Bebida( "Coca-Cola", 1.5, 18 );
        Shampoo shampoo = new Shampoo ( "Shampoo Sedal", 500, 19 );
        Fruta frutilla = new Fruta( "Frutillas ", 64, "kilo" );
        System.out.println(colaZero);
        System.out.println(cola);
        System.out.println(shampoo);
        System.out.println(frutilla);
     }
}

java interface

asked by Matias Isnard 05.05.2018 в 01:33

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1 answer

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score 0 · Accepted Answer

The signature of the method compareTo of the interface Comparable states that it must return:

a negative number, zero, or a positive number if this object is less that, same as, or greater than the specified object.

So your implementation in Producto :

public int compareTo(Producto o) {
    return this.getPrecio() > o.getPrecio() ?
        1 : this.getPrecio() < o.getPrecio() ? -1 : 0;
}

Meets the definition.

Now, to take advantage of this interface to solve the problem of the highest and lowest price of Producto , you could use the methods of class Collections :

Collections.max(Collection col) :

returns the maximum element of the specified collection according to the natural order of its elements.

Collections.min(Collection col) :

returns the minimum element of the specified collection according to the natural order of its elements.

Given the above, you can create a collection with your Producto objects and then check for their maximum and minimum:

public static void main(String[] args) {
    Bebida colaZero = new Bebida( "Coca-Cola Zero", 1.5, 20 );
    Bebida cola = new Bebida( "Coca-Cola", 1.5, 18 );
    Shampoo shampoo = new Shampoo ( "Shampoo Sedal", 500, 19 );
    Fruta frutilla = new Fruta( "Frutillas ", 64, "kilo" );
    List<Producto> list = Arrays.asList(colaZero, cola, shampoo, frutilla);

    System.out.println("Producto con mayor precio: " + Collections.max(list));
    System.out.println("Producto con menor precio: " + Collections.min(list));
}