Java object name from user input as method call

Question

Been given the task of creating a Wallet class where you can create members and transfer money between them. The user can then pick who gives the money and who receives it. Here is a little of the relevant code:

Wallet adamsWallet = new Wallet("Adam", 403.50);
Wallet bentsWallet = new Wallet("Bent",  873);
Wallet clarksWallet = new Wallet("Clark", 319.50);


object_name_here.transfer(other_object_name_here, 200);

So I want the user for example to enter "adam" in the Scanner, then somehow append "sWallet" to adam and then use that as the object name for the method call.

How can I do that or is there a better way of doing it?

Jesper · Accepted Answer · 2012-12-06 12:31:27Z

7

Use a Map to store the wallets. For example:

Map<String, Wallet> wallets = new HashMap<>();

wallets.put("Adam", new Wallet("Adam", 403.50));
wallets.put("Bent", new Wallet("Bent",  873));
wallets.put("Clark", new Wallet("Clark", 319.50));

You can lookup a wallet by name from the map.

Wallet wallet1 = wallets.get("Adam");
Wallet wallet2 = wallets.get("Clark");

wallet1.transfer(wallet2, 200);

Note that objects do not have names - variables have names. An object is not a variable; a variable is a reference to an object. You can have multiple variables that refer to the same object.

answered Dec 6, 2012 at 12:31

Jesper

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2 Comments

Simon Forsberg Over a year ago

new HashMap<>(); assumes that Java 7 is being used. For older versions of Java, use new HashMap<String, Wallet>();

Duane Over a year ago

Thanks for your answer Jesper, it's very helpful and easy to understand. :)

jlordo · Accepted Answer · 2012-12-06 12:39:23Z

2

You can use a Map.

Map<String, Wallet> wallets = new HashMap<String, Wallet>();
wallets.put("Adam", new Wallet("Adam", 403.50));

However, in this case I recommend removing the "Adam" parameter for the Wallet constructor if possible. Let the wallet itself be independent from who's owning it.

Then you can get a persons wallet like this:

String name = "Adam"; // this string could be read from your Scanner object.
Wallet wallet = wallets.get(name); // You can also use wallets.get("Adam") directly of course.

edited Dec 6, 2012 at 12:39

jlordo

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answered Dec 6, 2012 at 12:30

Simon Forsberg

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Comments

Duncan Jones · Accepted Answer · 2012-12-06 12:42:10Z

Since the owner of the wallet is an entity in your system, I'd personally give them their own class. That allows more complex arrangements, such as multiple wallets being owned by one person, or storing additional metadata about the owner.

Your example would then be:

Map<Person, Wallet> wallets = new HashMap<Person, Wallet>();

wallets.put(new Person("Adam"), new Wallet(403.50));
wallets.put(new Person("Bent"), new Wallet(873));
wallets.put(new Person("Clark"), new Wallet(319.50));

Provided you have a sensible .equals() method defined in your Person class, you can find the wallet again:

Wallet wallet = wallets.get(new Person("Adam"));

I would also consider whether a Person class might contain a Wallet, rather than having a map linking people to wallets. The correct choice would depend upon your overall application goals. It may be more efficient to have a map for lookup purposes, but it might be more logical to store the wallet within the person, especially if a wallet cannot be owned by two people at the same time.

Bhavik Shah · Accepted Answer · 2012-12-06 12:34:36Z

0

You can create an hash map

HashMap<String,Wallet> hm=new HashMap<String,Wallet>();
hm.put("adams",adamsWallet);
...

then

   Wallet temp=hm.get("adams");

would return you the corresponding object

answered Dec 6, 2012 at 12:34

Bhavik Shah

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