SealedClass.java

// Which classes are permitted to extend this Liquid class, must be sealed/non-sealed/final.
public sealed class Liquid permits Water, Honey, Milk {}

// Now, Water can be extended by any class
public non-sealed class Water extends Liquid {}

// Honey is final. So, it can't be extended by anyone.
public final class Honey extends Liquid {}

// Milk is sealed. So, it starts another sealed hierarchy.
// Which class extends Milk, must be sealed/non-sealed/final.
public sealed class Milk extends Liquid permits Yogurt {}

// Yogurt completes sealed hierarchy, making itself final
public final class Yogurt extends Milk {}

// Tea can't extend Liquid class, as it was not permitted. But it can extend Water as this is non-sealed.
public class Tea extends Water {}