...
import android.hardware.Camera;

public class CameraInternal extends Camera {
}

...
import android.hardware.Camera;

public class CameraInternal extends Camera {

	CameraInternal() {
		super(); // тут ошибка: The constructor Camera() is not visible
	}	

	CameraInternal(int cameraId) 
	{
		super(  cameraId ); // тут ошибка: The constructor Camera(int) is undefined
	}
}

package android.hardware; 
.....

public class Camera { 
....
    Camera(int cameraId) {
        mShutterCallback = null;
        mRawImageCallback = null;
        mJpegCallback = null;
        mPreviewCallback = null;
        mPostviewCallback = null;
        mUsingPreviewAllocation = false;
        mZoomListener = null;

        Looper looper;
        if ((looper = Looper.myLooper()) != null) {
            mEventHandler = new EventHandler(this, looper);
        } else if ((looper = Looper.getMainLooper()) != null) {
            mEventHandler = new EventHandler(this, looper);
        } else {
            mEventHandler = null;
        }

        String packageName = ActivityThread.currentPackageName();

        native_setup(new WeakReference<Camera>(this), cameraId, packageName);
    }

    /**
     * An empty Camera for testing purpose.
     */
    Camera() {
    } 

....

private Camera cam;

private CameraInternal cam; // было бы в исходнике
private a b; // а стало бы после ProGuard если бы не .....

public class CameraInternal extends Camera

public class a extends Camera