我在尝试交换可观察列表中的元素时遇到异常？ [英] I get an exception when trying to swap elements in an observable list?

问题描述

我有以下代码，看起来很简单直接：

I have the following code, which seems very simple and straight-forward:

public static void main(String[] args) {
    Series<String, Number> series = new Series<String, Number>();
    ObservableList<Data<String, Number>> list = series.getData();

    list.add(new Data<String,Number>("1", new Double(1)));
    list.add(new Data<String,Number>("2", new Double(2)));
    list.add(new Data<String,Number>("3", new Double(3)));
    list.add(new Data<String,Number>("4", new Double(4)));
    int size = list.size();
    for (int i = 0; i < size-1; i++) {
        list.set(i, list.get(i+1));
    }
    list.remove(size-1);
}

问题是我在设置行时遇到空指针异常名单。这段代码不应该做它应该做的事情吗？我检查列表的大小，然后返回4.我唯一能想到的是我在这里遗漏了一些东西，不知道如何在指定的索引处正确设置元素？

The problem is that I get a null pointer exception at the line of setting the list. Shouldn't this code do what it's supposed to do? I check the size of the list and that returns 4. The only thing I can think of is that I'm missing something here and don't know how to properly set an element at the specified index?

你能帮助我吗？

编辑：
Stacktrace：

EDIT: Stacktrace:

Exception in thread "main" java.lang.NullPointerException
    at javafx.scene.chart.XYChart$Series$1.onChanged(Unknown Source)
    at com.sun.javafx.collections.ListListenerHelper$SingleChange.fireValueChangedEvent(Unknown Source)
    at com.sun.javafx.collections.ListListenerHelper.fireValueChangedEvent(Unknown Source)
    at javafx.collections.ObservableListBase.fireChange(Unknown Source)
    at javafx.collections.ListChangeBuilder.commit(Unknown Source)
    at javafx.collections.ListChangeBuilder.endChange(Unknown Source)
    at javafx.collections.ObservableListBase.endChange(Unknown Source)
    at javafx.collections.ModifiableObservableListBase.set(Unknown Source)
    at mypackage.Controller.main(Controller.java:657)

推荐答案

这个问题（特别是堆栈跟踪）看起来像是类似于 https://javafx-jira.kenai.com/browse/RT-35831 。我的机器上有8u20并测试了Stuart评论中给出的代码，也看不到异常。

This issue (in particular the stacktrace) looks like it resembles https://javafx-jira.kenai.com/browse/RT-35831 which has been fixed in JavaFX 8u20. I have 8u20 on my machine and tested the code given in Stuart's comment, and cannot see the exception either.

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