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//******Inheritance (cont.) - September 28th, 2016**********//
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-Liskov Substitution Principle (LSP)
    "Subtypes must be substitutable for their supertypes"
    -That's really a weird way to put it (though fun wordplay!), so instead, consider a method like:
    "public static Date vestDate(Employee e) {
        Date hireDate = employee.getHireDate();
        int vestYear = hireDate.getYear() + 2;
        return new Date (vestYear, hireDate.getMonth(), hireDate.getDay());
    }"
    -We can pass ANY type of employee to this- ANY class that inherits from employee (why different than polymorphism?)

There is a counterexample, though: if we have a 'Square' class that extends
    'Rectangle'; if I have a "setWidth" and "setHeight" methods and call them on a square, the PRECONDITION that we assume is that we can set the width/ height to be different. That doesn't work here.

We can specify an INTERFACE that gives any class that implements it that behavior, e.g.
    "public class Rectangle implements 2dshape", where 2dshape is an interface
    -An interface represent an OOP type, with a set of public method declarations (NOT implementations) that any object of the interface's type can support. E.G:
        ``"public interface 2dshape {
                double area();
            }"
    -You MUST define a class that implements the interface in order to use it; they CANNOT BE INSTANTIATED
    -Can override methods using @Override tag above method to implement methods
    -ALL INTERFACE METHODS ARE PUBLIC; if not given a publicity, it will be
        assumed public; will not compile with a private interface method
    -Cannot have a static interface method either
    -Can implement as many interfaces as we'd like
    -generally, use when class "has a" property, rather than "is a" object
-2 kinds: implementation and 'interface' interfaces
    -Extending a class means inheriting the interface and its implementation from the superclass
    -implementing an interface means getting only the interface itself

-If there are 2 methods with the same name/parameter that are NOT overridden, then the super class will win. Interfaces will clash.