java和线程: very strange behaviour

Question

        private synchronized Map<Team, StandingRow> calculateStanding() {
          System.out.println("Calculate standing for group " + getName());
          Map<Team, StandingRow> standing = new LinkedHashMap<Team, StandingRow>();

          for (Team team : teams) {
           standing.put(team, new StandingRow(team));
          }

          StandingRow homeTeamRow, awayTeamRow;
          for (Match match : matches.values()) {

           homeTeamRow = standing.get(match.getHomeTeam());
           awayTeamRow = standing.get(match.getAwayTeam());

           System.out.println("Contains key for " + match.getHomeTeam() + ": " + standing.containsKey(match.getHomeTeam()));
           System.out.println("Contains key for " + match.getAwayTeam() + ": " + standing.containsKey(match.getAwayTeam()));
                }
        }

这是我的代码。 matches 包含 6 个元素，但问题是，在两次匹配之后，站立 map 中不再找到任何键。

输出例如

Contains key for Zuid-Afrika: true
Contains key for Mexico: true
Contains key for Uruguay: true
Contains key for Frankrijk: true
Contains key for Zuid-Afrika: false
Contains key for Uruguay: false
Contains key for Frankrijk: false
Contains key for Mexico: false
Contains key for Mexico: false
Contains key for Uruguay: false
Contains key for Frankrijk: false
Contains key for Zuid-Afrika: false

这是在线程环境中，但是该方法是同步的，所以我认为这不会产生问题？我还对该方法进行了一个简单的单元测试，效果很好。

Answer 1

这几乎肯定不是线程问题。我几乎可以肯定问题出在您的团队类(class)中。它可能没有以正确的方式实现hashCode()/equals()。查看这两个方法的 javadoc 并相应地实现它们。