Is it possible to create an array which contains objects from several classes that don't necess-CodePudding

I currently have 7 different classes in my project, with 5 of those classes being related to each other (4 subclasses and 1 superclass) and the other two being related as well (1 subclass and 1 superclass). My assignment asks me to create an array which holds one object from each of these classes. My question is how can I create an array that can hold objects from unrelated classes? Here is a (much) shorter version of my code for example/clarity purposes:

//First superclass
package Plane;
public class Plane {
    
    
     private String brand;
     private double price; 
     private int horsepower;
    
     
    public Airplane() {
        brand = "example";
        price = 700000; 
        horsepower = 1750;
    }

    public Airplane(String airplaneBrand, double airplanePrice, int airplanePower) {
        this.brand = planeBrand;
        this.price = planePrice;
        this.horsepower = airplanePower;
    }

//Second superclass
package Boat;
public class Boat {

    private double weight;
    private double price;
    
    public Boat() {
        weight = 3475.6;
        price = 700000.99;
    }
    
    public Boat(double boatWeight, double boatPrice) {
        weight = boatWeight;
        price = boatPrice;
    }

The exact wording of the assignment is "Your array must include at least one object from each of the classes." From my understanding, this is what I described above as having one array that can hold objects from both the Plane class and the Boat class. The kicker is that I cannot import any of Java's built-in classes (i.e ArrayList, Hash Maps, etc.) I apologize in advance for any clarity issues as I'm only starting out with programming in general, I'd be happy to edit/add information if needed.

CodePudding user response：

In the code provided class is declared as

public class Plane

but constructors created:

public Airplane(){...}

and

public Airplane(String airplaneBrand, double airplanePrice, int airplanePower) {...}

constructor names should be same as class name.

Solution:

Create a Object[] array and use instanceof operator to find the class of the object :

import java.util.*;
class Airplane {


    private String brand;
    private double price; 
    private int horsepower;


    public Airplane() {
        brand = "example";
        price = 700000; 
        horsepower = 1750;
    }

    public Airplane(String airplaneBrand, double airplanePrice, int airplanePower) {
        this.brand = "AirIndia";
        this.price = airplanePrice;
        this.horsepower = airplanePower;
    }
    public String getBrand(){
        return brand;
    }

}
class Boat {

    private double weight;
    private double price;

    public Boat() {
        weight = 3475.6;
        price = 700000.99;
    }

    public Boat(double boatWeight, double boatPrice) {
        weight = boatWeight;
        price = boatPrice;
    }
    public double getWeight(){
        return weight;
    }
}


public class Test{
    public static void main(String ... $){
        var out = System.out;
        Object [] array = new Object[5];
        array[0] = new Boat();
        array[1] = new Airplane();
        array[2] = new Boat();
        array[3] = new String("Foo loves Bar");
        for(var o : array){
            if(o instanceof Boat b){
                out.println(b.getWeight());
            }
            if(o instanceof Airplane plane){
                out.println(plane.getBrand());
            }
            if(o instanceof String s){
                out.println(s);
            }

        }
    }
}

edit: thanks tgdavies for mentioning the efficient use of instanceof

output:

$ javac Test.java && java Test
3475.6
example
3475.6
Foo loves Bar