Java OCA OCP Practice Question 1959

Question

What is the output of the following application?

Assume /all-data exists and is accessible within the file system. 

package mypkg; /*ww w  .  java  2 s  .  com*/
import java.nio.file.*; 
import java.util.stream.Stream; 
public class Main { 
   public static Stream<String> readLines(Path p) { 
      try { 
         return Files.lines(p); 
      } catch (Exception e) { 
         throw new RuntimeException(e); 
      } 
   } 
   public static long count(Path p) throws Exception { 
      return Files.list(p) 
         .filter(w -> Files.isRegularFile(w)) 
         .flatMap(s -> readLines(s)) 
         .count(); 
   } 

   public final static void main(String[] day) throws Exception { 
      System.out.print(count(Paths.get("/all-data"))); 
   } 
}
  • A. The number of lines in all files in a directory tree
  • B. The number of lines in all files in a single directory
  • C. The code does not compile.
  • D. The code compiles but prints an exception at runtime.


B.

Note

The program compiles and runs without issue, making Options C and D incorrect.

The program uses Files.list() to iterate over all files within a single directory.

For each file, it then iterates over the lines of the file and counts the sum.

Option B is the correct answer.

If the count() method had used Files.walk() instead of Files.lines(), then the class would still compile and run, and Option A would be the correct answer.

Note that we had to wrap Files.lines() in a try-catch block because using this method directly within a lambda expression without a try-catch block leads to a compilation error.




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