Check if an object already exists with a specific property

Question

My program allows football coaches to be assigned to teams.

private String name;
private Team team;

public Coach(String name, Team team){
    this.name = name;
    this.team = team;
}

How do I check if a 'Coach' object with a specific 'Team' already exists. I want to stop two coaches from being assigned to the same Team.

String name = nameField.getText();
Team team = (Team) teamComboBox.getSelectedItem();

// I only want this to run, if the team doesn't already have a coach
Coach coach = new Coach(name, team);

I have spent hours reading similar questions but I haven't been able to get any of the code work. Any help would be appreciated, I'm pulling my hair out.

Answer 1

You'll have to store your coaches in some kind of collection. Given the specific use case you stated, a Map<Team, Coach> seems appropriate:

Map<Team, Coach> coachesByTeam = new HashMap<>();
if (!coachesByTeam.containsKey(team)) {
    Coach coach = new Coach(name, team);
    coachesByTeam.put(team, coach);
}

Answer 2

You need to use Set for this, for example

  Set<Team> teamsWithCoach = new HashSet<Team>();
  ...
  String name = nameField.getText();
  Team team = (Team) teamComboBox.getSelectedItem();

   if( !teamsWithCoach.contains(team) ) {
       Coach coach = new Coach(name, team); 
       teamsWithCoach.add(team);
   }