Interfaces

1. What is a Java interface? See S&W page 100 for an example. Note that an interface can have constants as well as methods, so the statement there that an "interface is nothing more than a list of instance methods" is not completely true.
2. Write a Java interface source file UnionFind.java to (as far as possible) express the API on page 219, the union-find API. Also rewrite just the first line of UF.java to assert that class UF implements this interface.
3. What methods/constructors of UF.java, page 221, are not in the interface?
4. Does WeightedQuickUF, page 228, qualify for implementing the interface? Explain why or why not.