I have some closed component which is working over some XML object. I need to expose this object outside of this component, but I don't want to allow changes on it outside of my component. How can I complete this?
Ensure your object has a copy constructor that allows you to make a deeply-cloned copy of your class.
Then call this when you return the object, eg
SomeClass instance = // ....
public SomeClass getInstance() {
return new SomeClass(instance);
}
This won't make the returned object immutable. But it doesn't need to be - you just don't want the external code making changes to your copy of the data.
Well, here is the access level's advocate ;-)
If you just wish to prevent the caller from making changes, it doesn't mean that it has to be immutable [in your package] - it just means that it shouldn't have a [public] way to mutate it :) I'm actually a growing fan of returning a limiting public interface .
For instance:
// Option A with a "limiting public interface"
public interface Awesome {
public String getText();
}
class MyAwesome implements Awesome {
public String getText() {
// ..
}
// Option B is to make setText non-public
public void setText() {
// ..
}
}
Then your code can return Awesome
which doesn't [directly] provide a way mutate the object.
I think you need to create another class which is immutable, taking your object as a parameter (maybe in constructor). Then you should only expose the instance of your new class.
Here's some tips to make an object immutable: Immutable class?
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