import java.util.ArrayList; public class AddTwoPolynomials { private double coeff; private int exp; public AddTwoPolynomials(double coeff, int exp) { this.coeff = coeff; this.exp = exp; } public double getCoeff() { return coeff; } public int getExp() { return exp; } public AddTwoPolynomials add(AddTwoPolynomials p) { this.coeff = this.coeff + p.getCoeff(); this.exp = this.exp + p.getExp(); return this; } @Override public String toString() { return "Coeff: " + coeff + "\tExp: " + exp; } public static void main(String[] args) { ArrayList al = new ArrayList(); al.add(new AddTwoPolynomials(5, 3)); al.add(new AddTwoPolynomials(21.2, 4)); al.add(al.get(0).add(al.get(1))); System.out.println("Sum of polynomials is " + al.get(2)); } } 

I need help understanding what is happening in this code line by line with a detailed explanation.