Inheritance

// this is pseudo code - isn

// base class references to derived-type objects.
BaseClass thing1 = new Derived1();
BaseClass thing2 = new Derived2();
BaseClass thing3 = new Derived3();

// assume the array elements must be of the same type
baseClassArray : [thing1, thing2, thing3];

for (int i-0; i< baseClassArray.Length; i++) {
    baseClassArray[i].Foo(); // base.Foo() is called.
}

for (int i=0; i< baseClassArray.Length; i++) {
    if (baseClassArray[i] is Derived1) {
        Derived1 thingy1 = (Derived1)baseClassArray[i];
        thingy1.Foo();   // derived Foo() called
    }else if ....
}

Polymorphism

// this is pseudo code - ish

public abstract class AbstractPainter {
   public abstract void Style();
}

public class Dali : AbstractPainter {
    public override Style() {
        console.writeline("floppy clocks lying about");
}

public class Warhol : AbstractPainter {
    public override Style() {
        console.writeline("High contrast soup cans");
    }
}

// cannot instantiate abstract classes
// ie.  new AbstractPainter() is not allowed.

AbstractPainter Salvador = new Dali();
AbstractPainter Andy = new Warhol();

AbstractPainterArray = [Salvador, Andy];

for (int i=0; i< AbstractPainterArray.Length; i++) {
    AbstractPainterArray[i].Style();
}

output:
    "floppy clocks lying about"
    "High contrast soup cans"

Inheritance

// this is pseudo code - isn

// base class references to derived-type objects.
BaseClass thing1 = new Derived1();
BaseClass thing2 = new Derived2();
BaseClass thing3 = new Derived3();

// assume the array elements must be of the same type
baseClassArray : [thing1, thing2, thing3];

for (int i-0; i< baseClassArray.Length; i++) {
    baseClassArray[i].Foo(); // base.Foo() is called.
}

for (int i=0; i< baseClassArray.Length; i++) {
    if (baseClassArray[i] is Derived1) {
        Derived1 thingy1 = (Derived1)baseClassArray[i];
        thingy1.Foo();   // the over-ride Foo() called
    }else if ....
}

Polymorphism

// this is pseudo code - ish

public abstract class AbstractPainter {
   public abstract void Style();
}

public class Dali : AbstractPainter {
    public override Style() {
        console.writeline("floppy clocks lying about");
}

public class Warhol : AbstractPainter {
    public override Style() {
        console.writeline("High contrast soup cans");
    }
}

// cannot instantiate abstract classes
// ie.  new AbstractPainter() is not allowed.

AbstractPainter Salvador = new Dali();
AbstractPainter Andy = new Warhol();

AbstractPainterArray = [Salvador, Andy];

for (int i=0; i< AbstractPainterArray.Length; i++) {
    AbstractPainterArray[i].Style();
}

output:
    "floppy clocks lying about"
    "High contrast soup cans"

###Take Away?###

Inheritance: Same-type references + derived objects, same method call.

polymorphism: Same-type references + derived objects, different method call.

// base class references to derived-type objects.
BaseClass thing1 = new Derived1();
BaseClass thing2 = new Derived2();
BaseClass thing3 = new Derived3();

// assume the array elements must be of the same type
baseClassArray : [thing1, thing2, thing3];

for (int i=0; i< baseClassArray.Length; i++) {
    //language specific way of testing for & casting back to derived type
    // call derived Foo()
}

Inheritance

// this is pseudo code - isn

// base class references to derived-type objects.
BaseClass thing1 = new Derived1();
BaseClass thing2 = new Derived2();
BaseClass thing3 = new Derived3();

// assume the array elements must be of the same type
baseClassArray : [thing1, thing2, thing3];

for (int i-0; i< baseClassArray.Length; i++) {
    baseClassArray[i].Foo(); // base.Foo() is called.
}

for (int i=0; i< baseClassArray.Length; i++) {
    if (baseClassArray[i] is Derived1) {
        Derived1 thingy1 = (Derived1)baseClassArray[i];
        thingy1.Foo();   // derived Foo() called
    }else if ....
}

Polymorphism

// this is pseudo code - ish

public abstract class AbstractPainter {
   public abstract void Style();
}

public class Dali : AbstractPainter {
    public override Style() {
        console.writeline("floppy clocks lying about");
}

public class Warhol : AbstractPainter {
    public override Style() {
        console.writeline("High contrast soup cans");
    }
}

// cannot instantiate abstract classes
// ie.  new AbstractPainter() is not allowed.

AbstractPainter Salvador = new Dali();
AbstractPainter Andy = new Warhol();

AbstractPainterArray = [Salvador, Andy];

for (int i=0; i< AbstractPainterArray.Length; i++) {
    AbstractPainterArray[i].Style();
}

output:
    "floppy clocks lying about"
    "High contrast soup cans"