Question of some stranger:

any one tell me I have number of files in a folder i want make a single file with all contents of number of file without using any loop, because of it is taking too much time please help me.

Ans:

You want to merge all files in some folder? 
It's impossible to do it in *usual* Java without a loop, because you have to iterate over all the files you want to merge. Maybe there is a way to do using some low-level filesystem functions, but even in this way you will have to iterate over the memory blocks representing the files.

Ans:

In Bash, i.e., below java, you can do: 

- cat '~/some-directory/some-file*' > one-file.csv 

or use find for more flexibility: 

- find ~/some-directory/ -name 'some-file*' | xargs cat >one-file.csv

Ans;

This sounds like an interview question asking for the knowledge of FileFilter class. The way you do it without a loop is shown below. If this is a more sophisticated question, then you may want to think about Windows journals which provides quicker access to files. 

public class AggregateFileContent 
{ 
public static void main(String[] args) 
{ 
String parentDirPath = args == null || args.length == 0 ? "/Users/alebedev/Documents/" : args[0]; 
aggregateContent(new File(parentDirPath)); 
} 

public static StringBuffer aggregateContent(final File parentDir) 
{ 
final StringBuffer allContent = new StringBuffer(); 
parentDir.listFiles(new FileFilter() 
{ 
@Override 
public boolean accept(File file) 
{ 
if (!file.isDirectory()) { 
try { 
String content = CharStreams.toString(new InputStreamReader(new FileInputStream(file), "UTF-8")); 
allContent.append(content); 
} 
catch (IOException e) { 
System.err.println("Failed to read file " + file.getParentFile().getAbsolutePath()); 
} 

} 

return true; 
} 
}); 

System.out.println(allContent); 
return allContent; 
} 
}