Answer:
Note that, you're to replace "at" with shift 2 as the brainly text editor can't Accept the symbol
Explanation:
import java.util.ArrayList;
abstract class Shape {
 private String name;
 public Shape(String name) {
   this.name = name;
 }
 public abstract double getArea();
 public abstract double getPerimeter();
 public String getName() {
   return name;
 }
}
class Circle extends Shape {
 private double radius;
 public Circle(String name, double radius) {
   super(name);
   this.radius = radius;
 }
 "at"Override
 public double getArea() {
   return Math.PI * radius * radius;
 }
 "at"Override
 public double getPerimeter() {
   // TODO Auto-generated method stub
   return 0;
 }
}
class Rectangle extends Shape {
 private double width;
 private double length;
 public Rectangle(String name, double width, double length) {
   super(name);
   this.width = width;
   this.length = length;
 }
 "at"Override
 public double getArea() {
   return width * length;
 }
 "at"Override
 public double getPerimeter() {
   // TODO Auto-generated method stub
   return 0;
 }
}
class Triangle extends Shape {
 private double size1;
 private double size2;
 private double size3;
 public double getSize1() {
   return size1;
 }
 public void setSize1(double aSize1) {
   size1 = aSize1;
 }
 public double getSize2() {
   return size2;
 }
 public void setSize2(double aSize2) {
   size2 = aSize2;
 }
 public double getSize3() {
   return size3;
 }
 public void setSize3(double aSize3) {
   size3 = aSize3;
 }
 public Triangle(String name, double size1, double size2, double size3) {
   super(name);
   this.size1 = size1;
   this.size2 = size2;
   this.size3 = size3;
 }
 public boolean isEquilateral() {
   return (size1 == size2 && size2 == size3);
 }
 "at"Override
 public double getArea() {
   double s, area;
   s = (size1 + size2 + size3) / 2;
   area = Math.sqrt(s * (s - size1) * (s - size2) * (s - size3));
   return area;
 }
 "at"Override
 public double getPerimeter() {
   // TODO Auto-generated method stub
   return 0;
 }
}
public class ShapeClient
{
 public static void main(String[] args) {
   ArrayList<Shape> shapeList = new ArrayList<Shape>();
   Shape s1 = new Circle("circle 1", 10);
   shapeList.add(s1);
   Shape s2 = new Rectangle("rectangle 2", 100, 100);
   shapeList.add(s2);
   Shape s3 = new Triangle("Triangle 3", 11, 12, 10);// these are sides
                             // that need to be
   Triangle t= (Triangle)(s3);                        // compared
   if(t.getSize1()==t.getSize2() && t.getSize2()==t.getSize3()){
     shapeList.add(s3); // this is where i am stuck
   }
   if (!s1.getClass().isInstance(s2)) {
     System.out.println("Actual types of s1 and s2 are different");
   }
 }
}
Console X td> ShapeClient (2) Java Application] CASoft PegaEclip Actual types of s1 and s2 are different
Kindly check the image below to see the output.
