CODEWITHSUNDEEP
java-me
Stephen Solomon
Stephen Solomon

Reputation: 163

How can I find out if there are any objects of a class (memory) being referenced or not in j2me?

I am working on a custom text field for a touch device and this text field is to be used in games. This custom text field is a class and has a variable in which the keypad image is stored which is static variable, if I have to display 2 text field in one page(screen) I’ll have to create 2 objects of the text field class and since the keypad image is stored in a static variable it would be shared by both the objects, now I want to know, if any objects are created of the custom keypad class, are these objects(memory) being referenced by any variable, if not I want to free the image memory and reload it when a new object is created.

Upvotes: 4

Views: 153

Answers (2)

Frank Pavageau
Frank Pavageau

Reputation: 11715

If you have access to WeakReference, you could keep a static WeakReference to the image in your class, and have a non-static (strong) reference in instances of your class:

public class CustomTextField {
    // Only necessary if multiple threads can create UI elements
    private static final Object lock = new Object();
    private static WeakReference<Image> keypadRef;

    private final Image keypad;

    public CustomTextField() {
        this.keypad = loadKeypad();
    }

    private static Image loadKeypad() {
        Image keypad = null;
        // Same comment as above: you don't need the lock if the UI elements are
        // not created in multiple threads.
        synchronized (lock) {
            if (keypadRef != null) {
                keypad = keypadRef.get();
            }
            // Either there was no existing reference, or it referenced a GCed
            // object.
            if (keypad == null) {
                keypad = new Image();
                keypadRef = new WeakReference(keypad);
            }
        }
        return keypad;
    }
}

That makes the keypad image eligible to garbage collection as soon as there are no instances referencing it, otherwise it's kept around and shared between instances.

Upvotes: 2

funkybro
funkybro

Reputation: 8671

IMO for a Java ME app you should have enough understanding of the codebase to know for yourself when memory-hungry objects like images can be freed.

Upvotes: 1

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