java完成一个程序，打印一个树状的目录结构。子目录与父目录之间有两个空格的缩进。

import java.io.File;

/**
*完成一个程序，打印一个树状的目录结构。子目录与父目录之间有两个空格的缩进
*/
public class TreeDir {

public static void main(String[] args) {
String pathname = “C:/Documents and Settings/user/桌面/Lecture notes/”;
File f = new File(pathname);
System.out.println(f.getName());
TreeDir.tree(f,0);
}
private static void tree(File f,int level) {
File[] childs = f.listFiles();
level++;
int j = 0;
String preStr = “”;
while(j < level){
preStr += “——–”;
j++;
}
for (int i = 0; i < childs.length; i++) {
System.out.println(preStr + childs[i].getName());
if (childs[i].isDirectory()) {
tree(childs[i],level);
}
}
}
}