Question

我在JDK 1.7中使用Java Collections时出错：我在这一行中得到了这个例外： proposalStatuses.addAll（getAllSubmittedStatuses（））

java.lang.UnsupportedOperationException
        at java.util.AbstractList.add(Unknown Source)
        at java.util.AbstractList.add(Unknown Source)
        at java.util.AbstractCollection.addAll(Unknown Source)

尝试将一个集合添加到列表中

/**
     * Gets the all submitted statuses.
     *
     * @return the all submitted statuses
     */
    private Collection<ProposalStatus> getAllSubmittedStatuses() {

        return Arrays.asList(
                  ProposalStatus.SAVED_TO_IOS
                , ProposalStatus.SENDED_TO_IOS_IN_PROGRESS
                );
    }

    /**
     * Gets the all received statuses.
     *
     * @return the all received statuses
     */
    private Collection<ProposalStatus> getAllReceivedStatuses() {

        Collection<ProposalStatus> proposalStatuses =

                Arrays.asList(
                  ProposalStatus.RECEIVED_BY_IOS
                , ProposalStatus.SUBMITTED_TO_IOS
                , ProposalStatus.RECEIVED_IOS
                );

        proposalStatuses.addAll(getAllSubmittedStatuses());

        return proposalStatuses;
    }

Answer 1

来自javadoc of Arrays.asList()（强调我的）：

返回由指定数组
支持的固定大小列表

简而言之：您不能从此类列表中.add*()或.remove*()！您将不得不使用另一个可修改的List实现（例如ArrayList）。

Answer 2

为了解释一下，我正在使用你的代码：

private Collection<ProposalStatus> getAllSubmittedStatuses() {

    // This returns a list that cannot be modified, fixed size
    return Arrays.asList(
              ProposalStatus.SAVED_TO_IOS
            , ProposalStatus.SENDED_TO_IOS_IN_PROGRESS
            );
}

/**
 * Gets the all received statuses.
 *
 * @return the all received statuses
 */
private Collection<ProposalStatus> getAllReceivedStatuses() {

    // proposalStatuses will be a fixed-size list so no changing
    Collection<ProposalStatus> proposalStatuses =

            Arrays.asList(
              ProposalStatus.RECEIVED_BY_IOS
            , ProposalStatus.SUBMITTED_TO_IOS
            , ProposalStatus.RECEIVED_IOS
            );

    // This will not be possible, also you cannot remove anything.
    proposalStatuses.addAll(getAllSubmittedStatuses());

    return proposalStatuses;
}

出于您的目的，我会执行以下操作：

return new ArrayList<ProposalStatus>(Arrays.asList(ProposalStatus.SAVED_TO_IOS,ProposalStatus.SENDED_TO_IOS_IN_PROGRESS)

这可以帮助您获取Collection对象。

Answer 3

Arrays.asList()返回一个您无法修改的不可变列表。

更具体地说，没有实现add（），addAll（）和remove（）方法。

带有Collection对象的Java UnsupportedOperationException

3 个答案: