如何比较两个数组列表，这些数组列表包含属于同一超类但属于各种子类的对象的实例。

Question

So far I came up with that.

public static boolean challenge(ArrayList<Thing> required, ArrayList<Thing> owned){

    boolean result=false;

    for(int i=0; i<=required.size(); i++)
    {
        for(int j=0; j<=owned.size(); j++)
        {
            ///compare each required to all owned
            ///if (required.get(i) instanceof owned.get(j))
            {   result=true;
            }

            /// else
            {
                result=false;
                break;
            }
        }   
    }

    return result;
}

it gives me compile error in the if statement. " ')' expected "

I am a bit lost. Any help would be appreciated.

Answer 1

You may want to use required.get(i).getClass() == owned.get(j).getClass() instead.

Also consider using 'for each' eg

for(Thing r : required) {
    for (Thing o : owned) {
      if (r.getClass() ...
        ...
    }
}

Answer 2

As Alex Nevidomsky said, instanceof should be used with the type on the right part. Should be if (required.get(i) instanceof owned.get(j).getClass()) maybe this link will be helpful also