Class Diagram and Class Relationships

UML Representation

Link

• An instance of an association
• Exists between two or more objects

public class Member {
    private Book book;
    void issueBook(Book b) {
        this.book = b;
        b.setLender(this);
    }
}
public class Book {
    private Member member;
    void setLender(Book b) {
        member = b;
    }
}

Qualified Association

Using a unique identifier to represent an association

public class League {
    private Map players;
    void addPlayer(String name, Player p) {
        players.put(name, p);
        p.addLeague(nickName, this);
    }
}

public class Player {
    private Map league;
    void addLeague(String nickName, League l) {
        league.put(l, nickName);
        l.addPlayer(nickName, this);
    }
}

Interface

A strict contract that is implemented by classes. Must override the defined methods

Abstract Class

A restricted base class that cannot be directly instantiated and is designed to inherited

• Reduces complexity
• Increases flexibility