检查集合中是否存在 java 个对象

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检查，但我想 Java 中有更好的方法 8. 有没有人建议如何以优雅的方式检查它？

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

试试这个 anyMatch 的 Lambda 表达式(Java 8)。

Returns whether any elements of this stream match the provided predicate. May not evaluate the predicate on all elements if not necessary for determining the result. If the stream is empty then false is returned and the predicate is not evaluated.

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

Answer 2

您需要在 UserSelected class 中正确实施 equals 和 hashCode 方法。之后，您可以使用 preparedUserSelected.contains(userSelectedToCheck).

轻松检查是否存在

下面是 equals/hashCode 的示例实现，适用于您的 class：

@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());
}

检查集合中是否存在 java 个对象

Check if java object exists in the Set

java

set

java-8