Adding object/class to a list with a different type

Question

Basicly, I want to how if it's possible in Java to do following:

public static ArrayList<Script> scripts = new ArrayList<Script>();
scripts.add(new TestScript()); //TestScript extends Script class.

I've tried some different things with type casting, and asking some of my friends. No one seem to have an answer. But I know it would be possible.. maybe? If so, how do I make the above work? If it doesn't, what else can I do to get the same effect?

Have you tried to run your code? Why ask us if it works?

rolfl
– rolfl

2013-11-02 18:49:54 +00:00
Commented Nov 2, 2013 at 18:49 — rolfl
– rolfl, Commented Nov 2, 2013 at 18:49

Juned Ahsan · Accepted Answer · 2013-11-02 18:49:00Z

2

TestScript should be a subclass of Script. A collection of an object can hold the objects of the same class and all of its subclasses.

No casting is required because TestScript is logically a Script as it extends from Script.

answered Nov 2, 2013 at 18:49

Juned Ahsan

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3 Comments

L.Butz Over a year ago

It is already mentioned in the question, that TestScript extends Script. See line #2 of his code snippet.

nanofarad Over a year ago

The question may be calling TestScript methods on the elements.

Kevin Jensen Petersen Over a year ago

Exactly. My TestScript extends Script, which in theory should work, but doesn't. Can it be something to do, that my script above, which is a "ScriptManager" is in a subfolder, but the TestScript is in the root?

Masudul · Accepted Answer · 2013-11-02 18:58:09Z

1

Your declaration should be ArrayList<? super Script>

edited Nov 2, 2013 at 18:58

answered Nov 2, 2013 at 18:49

Masudul

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2 Comments

Josh M Over a year ago

I wouldn't say should.

nanofarad Over a year ago

Masud: No, it won't work. Try it. Adding TestScript instances won't work, since it could be an ArrayList<FooScript> where FooScript extends Script but not TestScript.

nanofarad · Accepted Answer · 2013-11-02 18:50:32Z

0

Yes, this will work. You'll do as follows:

public static ArrayList<Script> scripts = new ArrayList<Script>();
scripts.add(new TestScript()); //TestScript extends Script class.

and to traverse,

for( Script scr : scripts){
    scr.someMethodOfScript(); //no testscript methods available
    if(scr instanceof TestScript){
        TestScript tscr = (TestScript) scr;
        //call TestScript methods on tscr
    }
}

You'll need an instanceof and a cast for any TestScript methods not available in Script.

answered Nov 2, 2013 at 18:50

nanofarad

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