Lambda Expression & Streams - Data Manipulation - Learning-2

Let us see another example of Lambda expressions using the concept of Listing of Directories using Java Files.

Without Lambda Expression

private void listDirectories() {

File[] directories = new File(".").listFiles(new FileFilter() {

@Override

public boolean accept(File pathname) {

return pathname.isDirectory();

}

});

}

Here we create the FileFilter object and override the accept method based on our criteria.

With Lambda Expression

private void listDirectoriesUsingLambda() {

File[] directories = new File(".").listFiles(File::isDirectory);

}

Instead of creating the FileFilter Object simply call the required API. "File::isDirectory" is one of the lambda expression to check if the given file is a directory or not. 

In the method-1, object is passed and verified and in method-2 the functionallity is passed and it acts on each object in the list.

Full code is given below

import java.io.File;

import java.io.FileFilter;

import java.io.IOException;

import java.util.stream.Stream;

public class FileOperations {

public FileOperations() {

}

private void listDirectories() {

File[] directories = new File(".").listFiles(new FileFilter() {

@Override

public boolean accept(File pathname) {

return pathname.isDirectory();

}

});

printFiles(directories);

}

private void listDirectoriesUsingLambda() {

File[] directories = new File(".").listFiles(File::isDirectory);

printFiles(directories);

}

private void printFiles(File[] files) {

Stream<File> fileStream = Stream.of(files);

fileStream.forEach(x-> {

try {

System.out.println(x.getCanonicalPath());

} catch (IOException e) {

e.printStackTrace();

}

});

}

public static void main(String[] args) {

FileOperations fileOperations = new FileOperations();

System.out.println("Listing Directories without lambda expression");

System.out.println("---------------------------------------------");

System.out.println("");

fileOperations.listDirectories();

System.out.println("");

System.out.println("Listing Directories with lambda expression");

System.out.println("---------------------------------------------");

System.out.println("");

fileOperations.listDirectoriesUsingLambda();

}

}