Understanding Polymorphism in Java Programming

1. Polimorphism

2. POLYMORPHISM • What is polymorphism ? • The feature that allows an object of a certain class to be seen also as an object of another • Why do we need it ? • Sometimes it makes programming easier • Example • We are dealing with different kinds of animals in a farm • We want to do the same things with them but they will react differently

3. Dealingwithanimals • Counthowmanylegswehave in total in a list of animals intlegs(Animal[] x) { //x isanarray of Animal objects intnlegs = 0; for(int i = 1; i < x.length; i++) if (x[i].name,equals(“Cat”)) nlegs += 4; elseif (x[i].name.equals(“Cock”)) nlegs+= 2; elseif (. . . • Whathappensifwehave a new type of animal ?

4. ApplyingPolymorphism • Letshaveeach animal defined as a differntclassbutall of themhave a methodcalledlegs() ClassCockextends Animal { . . . publicintlegs() { return 2; } . . . } intlegs(Animal[] x) { int n = 0; for(int i = 1; i < x.length; i++) n += x[i].legs(); return n; }

5. Resources in Java • In java we can haveanobject of class “Pig” and anobject of class “Cock” which can beealsoseen as of class “Animal” (thushavingthesamemthodsbutreactingdiffernt to it) by: • Simple inheritance: Animal declares nlegs(), Pig and Cockoverwriteit • Abstractclass: Animal declares nlegs() as abstract, Pig and Cockoverwriteit • No differencewith 1 whenwritingPig and Cock, • Preventusersfromcreating Animal objects • Interface: instead of writingclass Animal wewrite interface Animal which declares methodnlegs(), Pig and Cockimplementit

6. Letsseethe case of figures withall 3 • Wewillhave a base classGfigure • Fromthisonewewill “derive” Grectangle, Gcircle and Gtriangle • Theyhave a originpoint (x,y) and can be drawnover a Consoleobject • Consoleclasscreatedforthis lectura to easydrawings • Wewant to easilyresize and move figures ontheConsole • Folder figures simple inheritanceimplementsthiswith simple inheritance • Folder figures abstractclassesimplementsthiswithanabstractclass • Folder figures interface implementsthiswithan interface