检查Set中是否存在Java对象

Question

我有一个Set ，我将检查是否仍然存在具有相同属性的Object 。 我的第一种方法是遍历列表并进行检查，但是我想Java 8中有更好的方法。有人建议如何以一种优雅的方式检查它吗？

final Set<UserSelected> preparedUserSelected = new HashSet<>();

    UserSelected userSelected1 = new UserSelected();
    userSelected1.setInstitutionId("1");
    userSelected1.setUserId("1");
    userSelected1.setChatMessageFilter(ChatMessageFilterEnum.TYP2);

    UserSelected userSelected2 = new UserSelected();
    userSelected2.setInstitutionId("2");
    userSelected2.setUserId("2");
    userSelected2.setChatMessageFilter(ChatMessageFilterEnum.TYP1);

    UserSelected userSelected3 = new UserSelected();
    userSelected3.setInstitutionId("3");
    userSelected3.setUserId("3");
    userSelected3.setChatMessageFilter(ChatMessageFilterEnum.TYP2);

    preparedUserSelected.add(userSelected1);
    preparedUserSelected.add(userSelected2);
    preparedUserSelected.add(userSelected3);

    UserSelected userSelectedToCheck = new UserSelected();
    userSelectedToCheck.setInstitutionId("2");
    userSelectedToCheck.setUserId("2");
    userSelectedToCheck.setChatMessageFilter(ChatMessageFilterEnum.TYP1);

    boolean contains = false;
    for (final UserSelected userSelected : preparedUserSelected) {
        if (userSelectedToCheck.getInstitutionId().equals(userSelected.getInstitutionId())
            && userSelectedToCheck.getUserId().equals(userSelected.getUserId())
            && userSelectedToCheck.getChatMessageFilter() == userSelected.getChatMessageFilter())
            contains = true;
    }

    System.out.println("contains: " + contains);

Answer 1

您需要在UserSelected类中正确实现equals和hashCode方法。 之后，您可以使用preparedUserSelected.contains(userSelectedToCheck)轻松检查其是否存在。

这是您的类的equals/hashCode的示例实现：

@Override
public int hashCode() {
    return Objects.hash(getUserId(), getInstitutionId(), getChatMessageFilter());
}

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null || getClass() != obj.getClass())
        return false;
    UserSelected other = (UserSelected) obj;
    return Objects.equals(getChatMessageFilter(), other.getChatMessageFilter()) &&
            Objects.equals(getInstitutionId(), other.getInstitutionId()) &&
            Objects.equals(getChatMessageFilter(), other.getChatMessageFilter());
}

Answer 2

试试这个Lambda Expression（Java 8）的任何匹配项。

返回此流的任何元素是否与提供的谓词匹配。 如果不需要确定结果，则可能不会对所有元素都评估谓词。 如果流为空，则返回false，并且不对谓词求值。

boolean isExist = preparedUserSelected.stream()
            .anyMatch(userSelected -> userSelected.getInstitutionId().equalsuserSelected.getInstitutionId());