Naming objects different names when creating in a method

Question

I'm trying to create a Person-object inside of a method called on, and then i want to add that person to a list of participants.

public void addPerson(String name, int age){
        //Adding person in a list of participants, capping it at 99 participants
        int i = 0;
        if (i<100) {
            Person participant = new Person(name, age);
            participants.add(participant.getName());  
            this.newest= deltager;
            i++;     
        }
    }

If i want to call on a specific participant after having filled up the list, how would i name the object so that they won't all be called "participant"? Wouldn't the object be overridden every time i add a new person, because the name of it would be the same?

that name is irrelevant. and no, they won't overwrite each other. — Stultuske
– Stultuske, Commented Apr 14, 2022 at 10:20
Objects don't have names, variables have names and the compiler will tell you if you try to declare the same variable name twice in the same scope (barring all sorts of special overriding and shadowing cases). — Kayaman
– Kayaman, Commented Apr 14, 2022 at 10:20
if (participants.size() < 100) {. You might consider returning a boolean, whether added. — Joop Eggen
– Joop Eggen, Commented Apr 14, 2022 at 10:28

stht55 · Accepted Answer · 2022-04-14 10:24:48Z

3

Person participant = new Person(name, age);

inside the function creates a local object. This object is initialized with the arguments from your function namely String name, int age.

However, your condition if (i<100) {...} will always be true. You initialize the local variable int i = 0; and then execute the code in the if-case which will always be the case.

If you where to write a for-loop like this:

for (int i = 0; i < 100; i++){
... }

You would create the same participant (same name and age given in the arguments in the function) 100 times.

answered Apr 14, 2022 at 10:24

stht55

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Comments

Basil Bourque · Accepted Answer · 2022-04-14 16:25:51Z

The Answer by stht55 is correct and important. Objects do not have a name while reference variables do.

Also note that your code is instantiating a Person object and then immediately discarding it after extracting the name. So there is no point to calling new Person in that code.

Loop collection

One solution is to loop the collection, interrogating each contained object for its member field name to see if it is a match.

List< Person > persons = 
    List.of(
        new Person( "Alice" , 42 ) ,
        new Person( "Bob" , 28 )
    )
;
for( Person p : persons ) {
    if( p.getName().equals( "Bob" ) { … we have a match … }
}

`Map`

Perhaps the data structure you want is a Map, a pairing of a key object that leans to value object.

Map < String , Person > map = new HashMap<>() ;

To use it, pass the name as key, and pass a new Person object as value.

map.put( name , new Person( name , age ) ) ;

Retrieval.

Person p = map.get( "Bob" ) ;

Beware of multiple objects coincidentally sharing the same key. In your case, several people might share the name “Bob”, but the map can store only one value per key. One way around this is to use a multimap, where the value paired with the key is a collection of value objects rather than a single. This has been covered many times already on Stack Overflow, so search to learn more.

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