Why does this function not work properly in an "if" statement

I try to call a function,"removeLineFromFile", to remove a line in a .txt file, given by @Narek, on: Find a line in a file and remove it (the second answer, by vote).

1) If I put it here, it works very well:

Part of the structure is:

public class cs1{
public static void main (String[] args) throws Exception{

         cs1 k = new cs1();
        ***k.removeLineFromFile(file1,args[0]);***   


      Testmain tf3 = new Testmain();

      if(tf4[1].length()!=0){  
               if(!tf4[1].trim().equals(tf5[3].trim())){  
                ...............

2) But if I put it in the if-else condition, it always return: "Could not delete file"

public class cs1{
public static void main (String[] args) throws Exception{


         cs1 k = new cs1();

      Testmain tf3 = new Testmain();

      if(tf4[1].length()!=0){  
               if(!tf4[1].trim().equals(tf5[3].trim())){  
                  ***k.removeLineFromFile(file1,args[0]);*** 
                ...............   

Could anyone tell me why? This is so odd.