Sealed classes and methods: Difference between revisions

=={{header|Java}}==

Classes and methods can be sealed in Java by using the 'final' keyword.

<syntaxhighlight lang="java">

import java.util.List;

public final class SealedClassesAndMethods {

public static void main(String[] args) {

List<MovieWatcher> movieWatchers = List.of( new ParentMovieWatcher("Donald"),

new ChildMovieWatcher("Lisa"),

new YoungChildMovieWatcher("Fred") );

for ( MovieWatcher movieWatcher : movieWatchers ) {

movieWatcher.watchMovie();

movieWatcher.eatPopcorn();

}

}

}

// Base class for MovieWatcher's

class MovieWatcher {

public MovieWatcher(String aName) {

name = aName;

}

public void watchMovie() {

System.out.println(name + " is watching the movie");

}

public void eatPopcorn() {

System.out.println(name + " is eating popcorn");

}

private final String name;

}

// ParentMovieWatcher cannot be extended because it is 'final'

final class ParentMovieWatcher extends MovieWatcher {

public ParentMovieWatcher(String aName) {

super(aName);

}

}

// ChildMovieWatcher can be extended.

class ChildMovieWatcher extends MovieWatcher {

public ChildMovieWatcher(String aName) {

super(aName);

name = aName;

}

// The method eatPopcorn() cannot be overridden because it is 'final'

public final void eatPopcorn() {

System.out.println(name + " is eating too much popcorn");

}

private String name;

}

class YoungChildMovieWatcher extends ChildMovieWatcher {

public YoungChildMovieWatcher(String aName) {

super(aName);

name = aName;

}

// The method watchMovie() cannot be overridden because it is 'final'

public final void watchMovie() {

System.out.println(name + ", you are too young to watch the movie.");

}

private String name;

}

</syntaxhighlight>

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<pre>

Donald is watching the movie

Donald is eating popcorn

Lisa is watching the movie

Lisa is eating too much popcorn

Fred, you are too young to watch the movie.

Fred is eating too much popcorn

</pre>