Extract Class

Code Smells

• A class is doing the work of several

Technique

• Create a new class
• Place the fields / methods responsible for the related functionality in it

Practice

• Open Player in moving.features package
• Extract “attributes” into a new class

@AllArgsConstructor
@Getter
@Builder
public class Player {
    private final String firstName;
    private final String lastName;
    private final LocalDate birthDate;
    private final int height;
    private final int weight;
    private final int rating;
    private final int pace;
    private final int shooting;
    private final int passing;
    private final int dribbling;
    private final int defending;
    private final int physicality;

    public boolean canDribble(Player otherPlayer) {
        return physicality + dribbling > otherPlayer.physicality + otherPlayer.defending;
    }
}

Shortcuts

• Right Click in the file
• Refactor | Extract Delegate
• Then configure the extraction
• More info here

Benefits

• Maintain adherence to the Single Responsibility Principle

Drawbacks

• Could create a lot of (Inline) classes

Hide Delegate

Code Smells

• Law of Demeter : call chain appears when a client requests an object from another object, then the second object requests another one, and so on.
  • Stuff like : person.getFirstAccount().getLastWithdrawal().getAmount()

    Any changes in these interrelationships will require changes on the client side.

Technique

For each method of the delegate-class called by the client

• Create a method in the `server-class that delegates the call to the delegate-class
• Change the client code so that it calls the methods of the server-class

Practice

• Open ChampionsLeague in moving.features package
• Hide Delegate

@AllArgsConstructor
@Getter
public class ChampionsLeague {
    private final List<Team> teams;

    public String nextStageTable() {
        return teams.stream()
                .map(team -> team.getName() + " - " + team.getLeague().getCountry())
                .collect(Collectors.joining("%n"));
    }
}

Benefits

• Hides delegation from the client
  • Make it easier to make changes to the system

Drawbacks

• Could lead to an excess of Middle Man

Remove Middle Man

Code Smells

• A class has too many methods that delegates to other objects

Technique

• Create a getter for accessing the delegate(s)
• Replace calls to delegating methods in the server-class

Practice

• Remove the Middle Man introduced in the previous exercise (in ChampionsLeague)

Shortcuts

• Open the class in the editor, and position the caret at the name of the delegating field
• On the main or context menu, select Refactor | Remove Middleman in Intellij

• More info here

Drawbacks

• Bound objects together