How can I access methods of different classes in java using the array of type Object

Question

Here is the code:

public static void main(String args[])
{
    Circle objCircle = new Circle(5);
    Square objSquare = new Square(5);
    Triangle objTriangle = new Triangle(3, 4);
    Sphere objSphere = new Sphere(5);
    Cube objCube = new Cube(5);
    Tetrahedron objTetra = new Tetrahedron(5);
    Object[] Shape = new Object[5];
    Shape[0] = objCircle;
    Shape[1] = objSquare;
    Shape[2] = objTriangle;
    Shape[3] = objSphere;
    Shape[4] = objCube;
    Shape[5] = objTetra;
    for(int i = 0; i<Shape.length; i++)
    {
       //Problem occured in this section of code
        System.out.println(Shape[i].getArea());
    }
}

}

I have six different classes and all of them have getArray() method with definition of their own. I want to print the values that getArray() method returns from different classes using the Shape array.

i have used abstract class. i have 6 classes. casting works if i cast for every class separately. — cnayak
– cnayak, Commented Apr 14, 2015 at 15:49
@Chandan: Well does your abstract class have a getArea() method? If so, just change your array to be an array of that type rather than Object[]. — Jon Skeet
– Jon Skeet, Commented Apr 14, 2015 at 15:49
The first problem I can see is an ArrayIndexOutOfBoundsException. Do not use Object[]. Use Shape[] or List<Shape> where Shape is an interface with a getArea method. — Paul Boddington
– Paul Boddington, Commented Apr 14, 2015 at 15:50
There are several problems with this code: 1. You're initializing the array to size 5 and trying to index 6 elements. This will invariably cause an ArrayIndexOutOfBoundsException. 2. Your array variable has a name starting with a capital letter. This should be reserved for class names, as it can be (and especially in this case is) confusing. 3. You cannot call getArea() like this, because you have declared your array to be of type Object[]. Object doesn't have the method getArea(). — Ray
– Ray, Commented Apr 14, 2015 at 15:53

Rishi Saraf · Accepted Answer · 2015-04-14 15:51:48Z

1

Define interface like below. Implement this interface in class Circle , Square ..

public interface Shape {

    public Double getArea();
}

Then you can different classes getArea as below.

Shape [] shape = new Shape [5];
    shape[0] = objCircle;
    shape[1] = objSquare;
    shape[2] = objTriangle;
    shape[3] = objSphere;
    shape[4] = objCube;
    shape[5] = objTetra;
    for(int i = 0; i<Shape.length; i++)
    {
       //Problem occured in this section of code
        System.out.println(Shape[i].getArea());
    }

answered Apr 14, 2015 at 15:51

Rishi Saraf

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2 Comments

user1869209 Over a year ago

Why use a Double instead of primitive double??

Rishi Saraf Over a year ago

its your choice I used it just for example :)

user4668606 · Accepted Answer · 2015-04-14 15:50:57Z

1

Use an interface or an abstract class and extend all different shapes from it.

public abstract class Shape{
    public abstract SomeType getArray();
}

And use

Shape[] Shapes

instead of Object[].

answered Apr 14, 2015 at 15:50

user4668606

Comments

score 0 · Accepted Answer · 2015-04-14 16:01:25Z

0

First of all you should avoid to use an Object[] What will happened if you do so?

 ...
shape[6] = Integer.parseInt(1);
for(int i = 0; i<shape.length; i++)
{
   //Oups a problem will occured here
    System.out.println(shape[i].getArea());
}

By using a Object[] you are not using the Java type safety. Every instance inherits from Object in Java which means that you can put everything in your Array.

I see that you put a variable with capitalize. It's break the Java convention capitalize is for Class, Enum, Interface. Maybe I am too orthodox :)

You can do the following:

public abstract Shape {
 public abstract double getArea();
}

public Circle extends Shape {
  public abstract double getArea(){
   //implementation here
  }
}

etc...

Depends of your use case. An Interface could be much more appropriate due to inheritance trade-offs in some case.

And use a List of Shape. You will ensure that you have the same type when you will call List.add method. Furthermore you can use a foreach loop

edited Apr 14, 2015 at 16:01

answered Apr 14, 2015 at 15:55

user1869209

1 Comment

cnayak Over a year ago

I used for each loop initially but i got this error: Can only iterate over an array or an instance of java.lang.Iterable.

cnayak · Accepted Answer · 2015-04-14 16:06:38Z

0

Thank you everyone i got it correct and i am posting my answer that i solved with your help

public static void main(String args[])
{

    Circle objCircle = new Circle(5);
    Square objSquare = new Square(5);
    Triangle objTriangle = new Triangle(3, 4);
    Sphere objSphere = new Sphere(5);
    Cube objCube = new Cube(5);
    Tetrahedron objTetra = new Tetrahedron(5);
    Shape[] a = new Shape[6];

    a[0] = objCircle;
    a[1] = objSquare;
    a[2] = objTriangle;
    a[3] = objSphere;
    a[4] = objCube;
    a[5] = objTetra;
    for(int i = 0; i<a.length; i++)
    {
        a[i].getArea();
    }


}

}

answered Apr 14, 2015 at 16:06

cnayak

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