Bean.java

public class Bean {
  private String field;

  public String getField() {
    return field;
  }

  public synchronized void setField(String field) {
    this.field = field;
  }

  public boolean equals(Object o) {
    return ((Bean) o).field.equals(field);
  }

  public int hashCode() {
    return field.hashCode();
  }
}