Polymorphism

Polymorphism

• instanceof
• equals

Classwork

In a role-playing game there will be various items for players to collect and use. It is up to you whether you are working on items for a fantasy, piracy, crime fighting, or other sort of game.

Part A

Write a class GameItem, representing an object in a role playing game that players may encounter. Every GameItem has a String name, an int value, and a boolean playerHas. (In this case, value could be a negative, indicating that it is worse than useless.)

Add methods pickup(), use(), and putdown(). Each checks playerHas to see if it can act successfully -- we can only pick up things we don't have, and only use or put down things we do have.  Each should print a message like "You have picked up the bag of magic beans" (using the name) if they are successful and a different message explaining failure otherwise.  If pickup is successful, playerHas becomes true, if putdown is successful, playerHas becomes false. 

Also write an equals method for this class. GameItems can only be equal to other GameItems, and only if they have the same name and value (but playerHas doesn't matter).  Don't forget to use .equals and == appropriately.

Part B
Write two classes that inherit from GameItem (things in a  game that someone might pick up and use - be as wacky as you like). To at least one of these, add a new instance variable appropriate to the class.

In each class, override at least one of pickup() and use() and putdown().  Print an appropriate message in each and set playerHas to true or false to reflect if we have picked up / put down the item.  Always check playerHas first to see if it is possible at all, but if there is another instance var, success should rely on that as well. 

For instance, a BagOfGold class might have its use() check the value, and if the value is 0, report that we threw away the empty bag (so playerHas became false), and otherwise use() might report that we spent some gold and decrease the value.

Or a Rock class might have a variable weight, and pickup() might only set playerHas to true if it is light enough -- if it is too heavy, we can't pick it up.

You could also have the other subclass make different choices about picking up/putting down, for instance  a SuperStickyGlueLump might have putdown never set playerHas to false, and print a message saying it is stuck to the player forever.

Add equals methods for each of the other classes, which require for equality that the other object be of the subclass type (not just GameItems).  Check that the equals you are overriding says they're the same (to handle the inherited instance vars) and check any added instance variable as well.

In a separate class, in a main method, create an array of GameItems allItems, which should have at least 5 items.  Make sure you have at least one for each of your classes.  

Also make one extra GameItem questItem outside of the array. Set up questItem so that it is equals to exactly one of the items in the array and has playerHas false.  (Not another pointer to the same object that is in the array, a different object but with instance vars set so that your equals method will return true!) 

Loop through the array and call pickup and use for each item, and then call putdown unless the item is equals to questItem.

At the end, print both the questItem we used to compare and the one equals to the questItem that we found in the array.  (for the first, playerHas should be false, for the second, it should be true)

[EC] Also keep (don't put down) an item if it is the most valuable item we have seen so far.  (It is possible for the questItem to be the most valuable item.)  Also print the final most valuable item at the end.

[EC] Each time we find a new most valuable item, go back and put down the previous most valuable item (but we would never put down the questItem).