Bug 45062 Don't filter output folder and class files
Create a Java project with source folder src and output folder bin. The bin folder will not be shown in the Packages Explorer. Create a Java project with source folder src and output folder output/bin. The output and bin folders are shown in the Packages Explorer. Implictly filtering out bin is confusing and inconsistent. A better way to do this would be to use a name filter for bin or add "Output folder" to the list of available filters.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/packageview/PackageExplorerPart.java
private void initDragAndDrop() {
		initDrag();
		initDrop();
	}
	private void initDrag() {
		int ops= DND.DROP_COPY | DND.DROP_MOVE | DND.DROP_LINK;
		Transfer[] transfers= new Transfer[] {
			LocalSelectionTransfer.getInstance(), 
			ResourceTransfer.getInstance(),
			FileTransfer.getInstance()};
		TransferDragSourceListener[] dragListeners= new TransferDragSourceListener[] {
			new SelectionTransferDragAdapter(fViewer),
			new ResourceTransferDragAdapter(fViewer),
			new FileTransferDragAdapter(fViewer)
		};
		fViewer.addDragSupport(ops, transfers, new JdtViewerDragAdapter(fViewer, dragListeners));
				}
	private void initDrop() {
		int ops= DND.DROP_COPY | DND.DROP_MOVE | DND.DROP_LINK | DND.DROP_DEFAULT;
		Transfer[] transfers= new Transfer[] {
			LocalSelectionTransfer.getInstance(), 
			FileTransfer.getInstance()};
		TransferDropTargetListener[] dropListeners= new TransferDropTargetListener[] {
			new SelectionTransferDropAdapter(fViewer),
			new FileTransferDropAdapter(fViewer)
		};
		fViewer.addDropSupport(ops, transfers, new DelegatingDropAdapter(dropListeners));