We want to realize a Java class PhotoGallery that represents an online photo gallery. Each PhotoGallery has an url (represented by a string), and contains photos, each represented simply as a string that denotes the link to the actual photo. The maximum number of photos a photo gallery may contain is fixed the moment the photo gallery is created. The functionalities of the objects of the class are:

• create: that takes as parameter a string representing an url and a positive integer n and creates a PhotoGallery object with the specified url, with a capacity to contain n photos, and with no photo initially stored;
• getUrl: that returns the url of the PhotoGallery;
• numPhoto: that returns the number of photos present in the PhotoGallery;
• add: that takes a photo (i.e., a string) as parameter, and adds it to the PhotoGallery, if it is not already present; otherwise it does not do anything; if there is no more room to store the photo, the gallery should not be changed, and a message should be printed on standard output;
• remove: that takes a photo (i.e., a string) as parameter, and removes it from the PhotoGallery, if it is present; otherwise it does not do anything;
• present: that takes a photo (i.e., a string) as parameter, and returns true if the photo is present in the PhotoGallery; false otherwise;
• returnAllPhotos: that returns an array containing all the photos (represented as strings) present in the PhotoGallery (note: the returned array should contain only the photos actually present);
• removeAll: that eliminates all photos from the PhotoGallery.

Part 1. Realize the class PhotoGallery.

Solution: representation of the objects, skeleton of the class, solution

Part 2. Realize a client class of the class PhotoGallery containing a static method readFromInput() that takes as parameter a PhotoGallery g, reads from standard input a set of photos (i.e., strings), one per line, stopping when the user inputs the empty string, and adds to g all photos read from input.

Solution

Part 3. Briefly discuss the difference between instance variables and local variables (with respect to initialization, lifetime, scope).