How to compare one value in an arraylist of objects to output largest value?

Question

I need to create a method getLargestObject() that finds the object in the array list with the largest area that returns its position and outputs the contents of the object. The current loop I am using doesn't work and I'm not sure how to compare the values of the areas in an arraylist so I can get the largest one.

package csu.cole;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Driver {
    public static void main(String[] args) throws FileNotFoundException {
        Scanner input = new Scanner(new File(
                "C:/Users/Charles/Desktop/GeometricObjectsData.txt"));

        ArrayList<GeometricObject> list = new ArrayList<GeometricObject>();


        while (input.hasNextLine()) {
            String line = input.nextLine();
            String[] tokens = line.split(", ");
            if (tokens[0].equals("CIRCLE")) {
                Circle c = new Circle();
                if (tokens.length == 4) {
                    float radius = Float.parseFloat(tokens[1]);
                    c.setRadius(radius);
                    String color = String.valueOf(tokens[2]);
                    c.setColor(color);
                    Boolean filled = Boolean.valueOf(tokens[3]);
                    c.setFilled(filled);
                    c.getArea();
                    list.add(c);
                    System.out.println(c.toString());
                } else if (tokens.length == 3) {
                    float radius = Float.parseFloat(tokens[1]);
                    c.setRadius(radius);
                    String color = String.valueOf(tokens[2]);
                    c.setColor(color);
                    Boolean filled = false;
                    c.setFilled(filled);
                    c.getArea();
                    list.add(c);
                    System.out.println(c.toString());
                } else if (tokens.length == 1) {
                    String color = "white";
                    c.setColor(color);
                    Boolean filled = false;
                    c.setFilled(filled);
                    c.getArea();
                    list.add(c);
                    System.out.println(c.toString());
                }
            } else if (tokens[0].equals("RECTANGLE")) {
                Rectangle r = new Rectangle();
                if (tokens.length == 5) {
                    float height = Integer.parseInt(tokens[1]);
                    r.setHeight(height);
                    float width = Integer.parseInt(tokens[2]);
                    r.setWidth(width);
                    String color = String.valueOf(tokens[3]);
                    r.setColor(color);
                    Boolean filled = Boolean.valueOf(tokens[4]);
                    r.setFilled(filled);
                    r.getArea();
                    list.add(r);
                    System.out.println(r.toString());
                } else if (tokens.length == 1) {
                    String color = "white";
                    r.setColor(color);
                    Boolean filled = false;
                    r.setFilled(filled);
                    r.getArea();
                    list.add(r);
                    System.out.println(r.toString());
                }
            }
            }

        }
        public int getLargestObject() {
            int max = Integer.MIN_VALUE;
            for (int = 0; i < list.size(); i++){
                if (list.get(i) > max){
                    max = list.get(i);
                }
            }
            return max;
    }
}

Use Collections#sort and pass it a custom Comparator that sorts the GeometricObject objects in reverse order, pull the first element of the list. If you do this on a copy of the original, you could even get it's original start position — MadProgrammer
– MadProgrammer, Commented Oct 15, 2014 at 4:26
@MadProgrammer Or just use Collections#max. O(n) is better than O(n log n), if you ask me. :-D — C. K. Young
– C. K. Young, Commented Oct 15, 2014 at 4:32
@ChrisJester-Young Depends on the result you're after, but since this won't change the original list, sounds like a much better idea ;) — MadProgrammer
– MadProgrammer, Commented Oct 15, 2014 at 4:34
How do I compare just one specific value of the objects in the ArrayList? I just want to get the object with the highest area. The objects have other parameters such as radius/height/width/color/filled as well as area. — ChaCol
– ChaCol, Commented Oct 15, 2014 at 4:43

ADDruid · Accepted Answer · 2014-10-15 05:08:46Z

1

Collections#max is fun, but advanced. Seems like you just need to change your if statement

 if (list.get(i) > max){

to use the area so

 if (list.get(i).getArea() > max){

But you said "returns its position and outputs the contents of the object" so use max to track the location, not the object so

    public int getLargestObjectIndex() {
        int maxIndex = 0;
        for (int = 1; i < list.size(); i++){
            // compare the area of the current index to the max index
            if (list.get(i).getArea() > list.get(maxIndex).getArea()){
                // if this one is bigger, save the location
                maxIndex = i;
            }
        }
        // output the contents of the object
        System.out.println(list.get(maxIndex).toString())
        // return the location
        return maxIndex;
   }

Note that this loop starts at i = 1 because maxIndex starts at 0

answered Oct 15, 2014 at 5:08

ADDruid

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7 Comments

C. K. Young Over a year ago

Heheh, "advanced". This kind of stuff makes me yearn for Ruby: list.max_by(&:area) (or, for more flexibility, list.max { |a, b| a.area <=> b.area }).

Kishan Bheemajiyani Over a year ago

@ChrisJester-Young can u explain it in detail plz

C. K. Young Over a year ago

@Krishna My point is that finding the object in a list with the maximum area is a one-liner in Ruby. It is also a one-liner in Java 8 (though not quite as short as the Ruby), but in older Java versions, it's just a PITA.

Kishan Bheemajiyani Over a year ago

@ChrisJester-Young ya u are saying true that finding object in list with max area will reduce the load of the Program rather comparing each. plz make me correct if i got anything wrong :)

ChaCol Over a year ago

Would I add this in my Driver class or my GeometricObject class, because if I add it to the Driver class it keeps saying illegal modifier, however if I add it to the GeometricObject class it doesn't have access to the ArrayList list.

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