File.isDirectory()

[Meena R. Krishnan]

import java.io.*;
public class FileTest2 {
public static void main(String[] args) {
  try{
    System.out.println("Files list");
    File f = new File("C:\\java");
  //  String[] files = f.list();
    File[] files = f.listFiles();
   
    for( int i=0;i<files.length;i++){
    if( files[i].isDirectory()){
    System.out.println("SubDirectory :" + files[i].getName() );
    File f3 = new File(files[i].getName()); ////Line 2
    File[] fArray = f3.listFiles();
    
    for(File ff:fArray){
    System.out.println(ff.getName()); ///Line 1
    }  
    }
    else{
    System.out.println(files[i].getAbsolutePath());  
    }
    }   
  }catch(Exception e){}
}
 
}
 

If I comment Line 1, I get the following output:

Files list
SubDirectory :Enthuware
C:\java\Example2.class
C:\java\Example2.java
C:\java\ExampleProgram.class
C:\java\ExampleProgram.java
C:\java\HelloWorldApp.class
C:\java\HelloWorldApp.java
SubDirectory   :-P	  rojects
SubDirectory :runtime-workspace
SubDirectory :SCJP 5.0
C:\java\Test.class
C:\java\Test.java
SubDirectory :Working

If I uncomment the same line, I get the following. Instead of printing files in the next level of subdirectory it not even printing the parent level.

Files list
SubDirectory :Enthuware

Any thoughts?


If I change Line 2 from (File f3 = new File(files[i].getName()) this to File f3 = files[i]; it works.

But I thought it will work even with the file name.
[ May 26, 2007: Message edited by: M Krishnan ]

[Percy Dadabhoy]

I tried it too....I got the latter result even when that line is commented...Making the change that you mentioned solves the problem...but I can't figure out why....

[Meena R. Krishnan]

>>.I got the latter result even when that line is commented

May be, you don't have any file under that directory. Try creating some files in that directory before trying the listFiles().

[John Stone]

because you are getting exception in your code
and your catch is {}, you have no idea it's there
put there e.printStackTrace() and you'll see error, most likely NullPointerException

[ramesh vardhan]

John said it right.
Nothing can be said until you do not handle the exception!

Possibly null is being returned by the method listFiles.

About the peculiar behavior of enhanced for loop like:
Code 1:
11.String s[]=null;
12.for(String ss : s){
13.System.out.println("Simple Stmt!!");
14.}
Throws a null pointer exception at runtime, at line 12.

Code 2:
11.String s[]=null;
12.for(String ss : s){
13.//System.out.println("Simple Stmt!!");
14.}
No exception thrown at runtime.

Can somebody please help in this regard.

[John Stone]

I get exception in both.
Possibly you are using some JDK with optimization, which ignores the empty for statement.

[ramesh vardhan]

Thanks John.
Yeah, behavior is same when I did not use any IDE.Probably the optimization for an empty for loop is set on my IDE.