流体输送管路的直径可根据流量和流速的大小来选定。

本题是一个Applet，它显示了一个树型结构。单击树结点的时候，就能将其子结点展开，同时下面的文本框可以显示出所单击的结点的路径，比如单击了根结点下B结点下B2结点，则文本框显示为“[TOP，B，B2]”。
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.tree.*;
public class java2 extends JApplet

JTree tree;
JTextField jtf;
public void init()

Container cp=getContentPane();
cp.setLayout(new BorderLayout());
______top=new DefauhMutableTreeNode("TOP");
DefauhMutableTreeNode a=new DefaultMutableTreeNode("A");
DefaultMutableTreeNode a1=new DefaultMutableTreeNode("A1");
a.add(a1);
DefaultMutableTreeNode a2=new DefaultMutableTreeNode("A2");
a.add(a2);
DefaultMutableTreeNode a3=new DefauhMutableTreeNode("A3");
a.add(a3);
DefaultMutableTreeNode b=new DefaultMutableTreeNode("B");
DefaultMutableTreeNode b1=new DefaultMutableTreeNode("B1");
b.add(b1);
DefaultMutableTteeNode b2=new DefaultMutableTreeNode("B2");
b.add(b2);
DefaultMutableTreeNode b3=new DefaultMutableTreeNode("B3");
b.add(b3);
top.add(a);
top.add(b);
tree=new JTree(top);
int v=ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED;
int h=ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED;
JScrollPane jsp=new JScrollPane(tree,v,h);
cp.add(jsp,BorderLayout.CENTER);
jtf=new JTextField(20);
cp.add(jtf,BorderLayout.SOUTH);
tree.addMouseListener(new MouseAdapter()

public void mouseClicked(MouseEvent me)

doMouseClicked(me);

);

void doMouseClicked(MouseEvent me)

______tp=tree.getPathForLocation(me.getX(),me.getY());
if(tp!=null)
jtf.setText(tp.toString());
else
jtf.setText("");