为什么不能将值从一个XYSeriesCollection复制到另一个? [英] Why can't I copy a value from one XYSeriesCollection to other?

问题描述

我正在使用JFreeChart在Java swing中创建图像直方图.为了创建它，我遍历所有像素以获得所有颜色.根据大小和位深度，它需要一些时间.

I'm using JFreeChart to create an image histogram in java swing. In order to create it I iterate over all pixels to get all the colors. Depending on the size and bit depth it takes some time.

一旦我拥有所有数据，就将其放入XYSeriesCollection变量中.为了能够稍后显示和隐藏某些系列，我保存了该变量的副本.

Once I have all the data I put it into a XYSeriesCollection variable. To be able to show and hide some series latter I save a copy of that variable.

我的问题是，如果我这样做:

My problem is that if I do it like this:

final XYSeriesCollection data = createHistogram();
final XYSeriesCollection dataCopy = createHistogram();

它可以正常工作，但是效率不高，因为我必须遍历所有像素，这需要一段时间.

It works without any problem, but it is not efficient, as I have to iterate over all pixels and that takes a while.

如果我只是这样复制它:

If I just copy it like this:

final XYSeriesCollection data = createHistogram();
final XYSeriesCollection dataCopy = data;

执行代码时出现此异常:

When I execute the code I get this exception:

Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: Series index out of bounds
at org.jfree.data.xy.XYSeriesCollection.getSeries(XYSeriesCollection.java:263)

我认为这是因为当我从数据中删除系列时，它们如何也从dataCopy中删除，但是那不应该完全不同吗?我只是使用这种方法:

I think that this is because when I delete the series from data some how they also get deleted from dataCopy but shouldn't those be completely different? I just work with this methods:

data.removeAllseries();
data.addSeries(dataCopy.getSeries(index));

例如，如果我创建:

int x = 5;
int y = x;
x=0;
System.out.println(y)

输出仍应为5，与x无关.我在做什么或假设那是错误的?

The output should still be 5 and it doesn't matter what I did with x. What am I doing or assuming that is wrong?

谢谢.

推荐答案

请注意 浅与深副本.您的示例dataCopy = data复制了 浅 .使用数据集的clone()方法制作 深 副本:

Note the difference between shallow versus deep copy. Your example, dataCopy = data, makes a shallow copy. Use the dataset's clone() method to make a deep copy:

XYSeriesCollection dataCopy = (XYSeriesCollection) data.clone();

您可以看到clone()的实现方式

You can see how clone() is implemented here. The fragment below creates a series, clones it, and updates the original to illustrate the effect.

代码:

XYSeriesCollection data = new XYSeriesCollection();
XYSeries series = new XYSeries("Test");
data.addSeries(series);
series.add(1, 42);
System.out.println(data.getSeries(0).getY(0));
XYSeriesCollection dataCopy = (XYSeriesCollection) data.clone();
series.updateByIndex(0, 21.0);
System.out.println(data.getSeries(0).getY(0));
System.out.println(dataCopy.getSeries(0).getY(0));

控制台:

42.0
21.0
42.0

还请考虑此处所示的方法，该方法可能更快.

Also consider the approach shown here, which may be faster.

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