Java Tutorial: Generics in java | Java Generics [Wildcard in Java Generics] ~ foundjava

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Java Tutorial: Generics in java | Java Generics [Wildcard in Java Generics] 

Shape.java

public abstract class Shape
{
    abstract void draw();
}

class Circle extends Shape
{
    void draw()
    {
        System.out.println("drawing circle");
    }
}

class Rectangle extends Shape
{
    void draw()
    {
        System.out.println("drawing rectangle");
    }
}

GenericDemo.java

import java.util.ArrayList;
import java.util.List;

public class GenericDemo
{

    public static void main(String args[])
    {
        List<Rectangle> recList = new ArrayList<Rectangle>();
        recList.add(new Rectangle());
        recList.add(new Rectangle());
        drawShapes(recList);

        List<Circle> circleList = new ArrayList<Circle>();
        circleList.add(new Circle());
        circleList.add(new Circle());       
        drawShapes(circleList);
    }

    /*
     * This method accepts only the list contains child class of Shape
     */
    public static void drawShapes(List<? extends Shape> shapeList)
    {
        for (Shape shape : shapeList)
        {
            shape.draw();
        }
    }

}

Output

drawing rectangle
drawing rectangle
drawing circle
drawing circle

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