CODEWITHSUNDEEP
javaarraylist
user3127109
user3127109

Reputation: 3763

indexOf for the objects of the ArrayList in java

I have an arrayList where three objects are passed.

List lst = new ArrayList();

Here the instances are added through for loop

Circle c1 = new Circle();
lst.add(c1);

Triangle t1 = new Triangle();
lst.add(t1)

Now how can I use the indexOf method or other way to find out which one is the circle, triangle and calculate the area of both and store it in an arraylist?

Upvotes: 2

Views: 594

Answers (4)

fantarama
fantarama

Reputation: 880

public interface Shape {
    Long area();
}

public class Circle implements Shape {
    public Long area() {
        return 0l; // your code here
    }
}

Same for Triangle class, then calculate area and put in another list...(java 8)

ArrayList<Shape> shapes = new ArrayList<>();
shapes.add(new Circle());
shapes.add(new Triangle());

ArrayList<Long> areas = new ArrayList<>();
areas.addAll(shapes.stream().map(s -> s.area()).collect(Collectors.toList()));

Upvotes: 1

SamTebbs33
SamTebbs33

Reputation: 5657

If you know that you will be inserting the Circle instances before the Triangle instances, then you can use even indexes to retrieve the Circle instances and odd indexes to retrieve the Triangle instances. Otherwise, you can loop through the list, check if each object is an instance of either class (e.g obj instanceof Circle) and then perform your area calculations.

for(Object obj : lst){
    if(obj instanceof Circle){
        Circle circle = (Circle)obj;
        // Perform the area calculations here
    }else if(obj instanceof Triangle){
        Triangle triangle = (Triangle)obj;
        // Perform the area calculations here
    }
}

Upvotes: -1

Metehan Toksoy
Metehan Toksoy

Reputation: 1935

Just call "indexof()" method. It can finds.

Upvotes: 1

Tim Biegeleisen
Tim Biegeleisen

Reputation: 520918

Assuming that the Circle and Triangle classes extend Shape, you could try this:

List<Shape> lst = new ArrayList<Shape>();

Shape c1 = new Circle();
Shape t1 = new Triangle();
lst.add(c1);
lst.add(t1);

for (Shape shape : lst) {
    if (shape instanceof Circle) {
        // handle the circle
    }
    else if (shape instanceof Triangle) {
       // handle the Triangle
    }
}

Upvotes: 2

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