WeightedDie solution

Complete the WeightedDie inheritance free response before reviewing the solution.

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`WeightedDie` solution

public class WeightedDie extends Die
{
    private int favoredSide;
    private double weight;
    
    public WeightedDie(int sides, int favoredSide, double weight)
    {
        super(sides);
        this.favoredSide = favoredSide;
        this.weight = weight;
    }
    
    public int getFavoredSide()
    {
        return favoredSide;
    }
    
    public int roll()
    {
        if(Math.random() < weight)
            return favoredSide;
        else
            return super.roll();
    }
}

Explanation

As with all problems that request an entire class, this problem should be solved using my Class writing order.

A subclass contains things that are new and things that are different.

Method headers

Subclasses do not inherit constructors, so all constructors are new.
Method getFavoredSide is new (not in Die).
Method roll is different. Method roll behaves differently in WeightedDie than method roll in Die. Method roll in WeightedDie overrides method roll in Die.

Instance variables

Instance variables can only be new. (There is no such thing as an instance variable that is different.) The subclass WeightedDie stores only the instance variables that are not already stored in Die.

WeightedDie must store the favored side and the weight. WeightedDie does not stores the number of sides, since that is already stored in Die.

Code inside methods

Constructor

Every subclass constructor must call a superclass constructor, either explicitly or implicitly. In this case, WeightedDie must explicitly call the Die constructor because there is no Die constructor with no parameters. The call must be the first line of the WeightedDie constructor.

The Die constructor accepts the number of sides. The WeightedDie constructor accepts the number of sides as its first parameter. The call super(sides); passes the number of sides to the Die constructor.

The WeightedDie constructor must also set its own instance variables (favoredSide and weight) .

`getFavoredSide` method

Method getFavoredSide is a simple accessor method that returns the favored side.

`roll` method

Method roll behaves as described in the problem. A random number is used for probability. See Generate random numbers with Math.random() for additional discussion. If the probability check passes, the favored side is returned.

If the probability check fails, the WeightedDie is rolled like a Die. Rolling like a Die is accomplished by calling the superclass roll method and returning the result.

Rewriting the code to roll like a Die is not acceptable. WeightedDie does not have access to the private instance variable sides in Die. WeightedDie should not store its own copy of the number of sides. A subclass should not duplicate state (instance variables) or behavior (methods) of its superclass.

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WeightedDie solution