CODEWITHSUNDEEP
java
Jhon N
Jhon N

Reputation: 11

Inheritance in Java with array

I have a problem when I use inheritance and define an object of parent class then call the constructor from the child class which has its own properties. When i want to assign values to the child class using sets methods its gives me an error (cannot find symbol) this is my code

    public class Shape {
private final double PI =3.14;
public Shape() {
}
public double getPI() {
    return PI;
} 
}

public class Rectangle extends Shape {
private double length;
private double width;
public Rectangle() {
}  
public double getLength() {
    return length;
}
public void setLength(double length) {
    this.length = length;
}
public double getWidth() {
    return width;
}
public void setWidth(double width) {
    this.width = width;
} 
}
public class Circle extends Shape{
private double radius;
public Circle(double radius) {
    this.radius = radius;
} 
public double getRadius() {
    return radius;
}
public void setRadius(double radius) {
    this.radius = radius;
}

}

public static void main(String[] args) {
    Scanner in=new Scanner(System.in);
    Shape s[] = new Shape[3];
    int type;
    for (int i = 0; i < s.length; i++) {
         System.out.println("Enter the Shape:\n 1.Rectangle \n 2.Circle");
         type = in.nextInt();
         if(type==1){
             s[i] = new Rectangle();
             s[i].setLength(5.5);
         }  
    }
}

Upvotes: 0

Views: 626

Answers (2)

AppleCiderGuy
AppleCiderGuy

Reputation: 1297

you setLength() method is present in your sub class Rectangle while s[i] points to an instance of type Shape which is a super class. thus, it doesn't recognize the instance method due to implicit upcasting. you will have to explicitly downcast you object s[i] from shape to Rectangle. This is how you can do it:

Rectangle r = (Rectangle)s[i];
r.setLength(5.5);

NOTE: Ofcourse the above statements gos after s[i] = new Rectangle();

an ideal way though (as explained by @Stultuske):

Rectangle r = new Rectangle();
r.setLength(5.5);
s[i] = r;

Upvotes: 0

Stultuske
Stultuske

Reputation: 9437

Your problem lies here:

s[i] = new Rectangle();
s[i].setLength(5.5);

Yes. You know that this form is an instance of Rectangle, all the JVM knows is that it's a Shape. If you want to use it as a Rectangle, you have to declare it as one:

Rectangle r = new Rectangle();
r.setLength(5.5);
s[i] = r;

EDIT: The reason for this is, when you declare an instance as a Shape (parent class), the JVM will consider it to be this, even if your code suggests (to a human reader) that a specific type will be used, the JVM will not make any assumptions on which sub class will be instantiated. You are limited to the possibilities of the class you declared it to be.

Since you now again save it as a Shape, in your array, if later on you'll want to get that value, you'll need to cast it.

Rectangle rNew = (Rectangle)s[index]; // of course after checking whether it is in fact a Rectangle

Upvotes: 1

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