CODEWITHSUNDEEP
javapolymorphism
Ciara
Ciara

Reputation: 197

Calling a subclass in Java polymorphism

I have a superclass Shape.Java that accepts color of a certain shape, and several subclasses that computes the area of different polygons. I created a main class, printing out different choices of polygons that the user wants to compute.

public static void choices() {
    System.out.println("What do you want to compute?");
    System.out.println("a. Rectangle");
    System.out.println("b. Triangle");
    System.out.println("c. Trapezoid");
}

I used a switch case for this.

case 'a': {
    System.out.print("Enter width: ");
    double width = input.nextDouble();
    System.out.print("\nEnter height: ");
    double height = input.nextDouble();
        .....
}

Problem is, how am I gonna call my subclass Rectangle(that extends the superclass Shape) that contains the methods that will display the input of the user and compute the area? Is this correct?

Shape rec = new Rectangle();

If it is, when I compile it I get an error 'cannot find symbol constructor Rectangle...'

Please help.

Upvotes: 4

Views: 171

Answers (1)

hvgotcodes
hvgotcodes

Reputation: 120198

You are doing it correctly. Your undefined symbol is probably the result of a bad or non-existent import; Perhaps Rectangle is not compiling, or perhaps you do not have a public no-arg constructor on Rectangle.

Because of dynamic dispatch, when you do

Shape rec = new Rectangle();

The interpreter, at runtime, will look at rec, and invoke the method on Rectangle, if you are invoking a method that was defined on Shape and then overwritten on Rectangle.

Upvotes: 3

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