javac编译器为什么找不到javafx.collections，但我正在使用它？

Question

这是我的代码的相关部分

package ReadWriteDisplayTriangles;

import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Polygon;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.collections;

class TrianglePane extends Pane{

    private RecordTable recordTable;

    //other code

    public void setToRecordTable() {
        ObservableList<Node> list = getChildren();
        int size = list.size();
        recordTable.setNewRecordArray(size);
        for(int i = 0; i < size; i++) {
            if(Debug.isDebug5() == true) {System.out.println("Observable list " + i + " is " + list.get(i)); }
        }
    }
}

这是javac -verbose的输出

[search path for class files: C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\resources.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\rt.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\sunrsasign.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\jsse.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\jce.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\charsets.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\jfr.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\classes,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\access-bridge-32.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\cldrdata.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\dnsns.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\jaccess.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\jfxrt.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\localedata.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\nashorn.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\sunec.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\sunjce_provider.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\sunmscapi.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\sunpkcs11.jar,C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\zipfs.jar,.]
[loading ZipFileIndexFileObject[C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\jfxrt.jar(javafx/scene/layout/Pane.class)]]
[loading ZipFileIndexFileObject[C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\jfxrt.jar(javafx/scene/paint/Color.class)]]
[loading ZipFileIndexFileObject[C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\jfxrt.jar(javafx/scene/shape/Polygon.class)]]
[loading ZipFileIndexFileObject[C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\jfxrt.jar(javafx/event/ActionEvent.class)]]
[loading ZipFileIndexFileObject[C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\jfxrt.jar(javafx/event/EventHandler.class)]]
TrianglePane.java:9: error: cannot find symbol
import javafx.collections;
             ^
  symbol:   class collections
  location: package javafx
[loading ZipFileIndexFileObject[C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\jfxrt.jar(javafx/scene/layout/Region.class)]]
[loading ZipFileIndexFileObject[C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\jfxrt.jar(javafx/scene/Parent.class)]]
[loading ZipFileIndexFileObject[C:\Program Files (x86)\Java\jdk1.8.0_241\jre\lib\ext\jfxrt.jar(javafx/scene/Node.class)]]

我有几个问题。

1. TrianglePane扩展窗格。在javafx.scene.layout.Pane的文档中，它作为方法getChildren（）列出，该方法返回一个ObservableList。由于扩展的类具有返回可观察列表的方法，因此为什么必须完全导入javafx.collections？
2. getChildren（）。add（...）在同一代码的其他部分中起作用，因此它必须以某种方式可以访问Observable List，对吗？
3. 为什么javafx.collections无法导入？我可以从javafx导入其他所有内容。
4. 我该怎么做才能修复我的编译器，库，或采取任何措施来利用此可观察列表的引用？

我正在使用jdk1.8.0_241

感谢您的任何投入，我是编码的新手，所以很爆炸。

Answer 1

要导入完整的软件包，您需要使用*：

import javafx.collections.*;

或者，通过其名称导入该类：

import javafx.collections.ObservableList;