CODEWITHSUNDEEP
javaobjectarraylist
Kaspazza
Kaspazza

Reputation: 323

Java creating instance of ArrayList from other class

The situation looks like this:

First class:

class Something {
    List<Object> names;
    public Something(){
       this.names = new ArrayList<Object>();    
    }
}

Second class I tried do something like that and it is not working:

class Main {
    public static void main(String[] args){
        Something names = new Something();
        ...
        for(Object name: names){
           ...
        }
    }
}

And it says that I can't iterate through "names" why? What am I doing wrong?

Upvotes: 2

Views: 2353

Answers (4)

Andy Turner
Andy Turner

Reputation: 140319

The other answers give fine solutions. But what if you do want to use just something in the enhanced for loop?

You have to make the class implement Iterable:

class Something implements Iterable<Object> {

And implement the iterator() method:

@Override public Iterator<Object> iterator() {
  return names.iterator(); // for example.
}

Now you can write:

for (Object object : something) { ... }

and it will be acceptable to the compiler.

But you should only do this if Something is-a Iterable of Objects, i.e. that it is intrinsically modelling something which should be iterated (e.g. it is "like a List"). Otherwise, if it merely has-a Iterable of Objects, stick to the other proposed solutions.

Upvotes: 2

pahan
pahan

Reputation: 567

Your Something class is not a List. But it contains a List.

class Something {
    List<Object> names;

    public List<Object> getNames(){
       this.names = new ArrayList<Object>();    
    }

    public void setNames( List<Object> list ){
       this.names = list;    
    }
}

class Main {
    public static void main(String[] args){
        Something somethingObj= new Something();
       List<Object> newNames = new ArrayList<>();
       newNames.add( new Object() );
       somethingObj.setNames( newNames ); 

        for(Object name: somethingObj.getNames()){
           ...
        }
    }
}

Upvotes: 1

Tim Biegeleisen
Tim Biegeleisen

Reputation: 521053

You probably intend to iterate over the list inside your Something class:

public static void main(String[] args){
    Something something = new Something();
    // then assign something.names to something
    ...
    for (Object name: something.getNames()) {
        // do something
    }
}

So, you probably want to expose a getter and setter for the names list in your class:

class Something {
    List<Object> names;

    public Something() {
        this.names = new ArrayList<Object>();    
    }

    public List<Object> getNames() {
        return names;
    }

    public void setNames(List<Object> names) {
        this.names = names;
    }
}

Upvotes: 2

Steven Spungin
Steven Spungin

Reputation: 29081

Try not to call your Something instance names. names is a member of the Something class instance. You are trying to iterate your Something class, and not names array inside it.

class Main {
    public static void main(String[] args){
        Something something = new Something();
        ...
        for(Object name: something.names){
           do smth;
        }
    }
}

Upvotes: 1

Related Questions