(Add package statement) Suppose you have Java source files under the directories chapter1, chapter2, . . . , chapter34

/*********************************************************************************
* (Add package statement) Suppose you have Java source files under the           *
* directories chapter1, chapter2, . . . , chapter34. Write a program to insert   *
* the statement package chapteri; as the first line for each Java source file    *
* under the directory chapteri. Suppose chapter1, chapter2, . . . , chapter34    *
* are under the root directory srcRootDirectory. The root directory and chapteri *
* directory may contain other folders and files. Use the following command to    *
* run the program:                                                               *
*                                                                                *
* java Exercise_12_18 srcRootDirectory                                           *
*                                                                                *
*********************************************************************************/
import java.util.*;
import java.io.*;

public class Exercise_12_18 {
	/** Main method */
	public static void main(String[] args) throws Exception {
		// Check command line parameter usage
		if (args.length != 1) {
			System.out.println("Usage java Exercise_12_18 srcRootDirectory");
			System.exit(1);
		}

		// Check if file object is a Directory
		File rootDir = new File(args[0]);
		if (!rootDir.isDirectory()) {
			System.out.println("Directory " + args[0] + " does not exist");
			System.exit(2);
		}

		// Create list of directories
		ArrayList<File> chapters = getDirectories(rootDir);
		
		while (!chapters.isEmpty()) {
			// Create array of chapter files
			ArrayList<File> files = getFiles(chapters);

			insertStatement(files, chapters.get(0));

			chapters.remove(0);
		}
	}

	/** Inserts a string as first line for each file in a list */
	public static void insertStatement(ArrayList<File> list, File dir) 
			throws Exception {
		for (int i = 0; i < list.size(); i++) {
			ArrayList<String> lines = new ArrayList<>();
			lines.add("package " + dir.getName() + ";");
			
			try (
				// Create input file
				Scanner input = new Scanner(list.get(i));
			) {
				while (input.hasNext()) {
					lines.add(input.nextLine());
				}
			}

			try (
				// Create input file
				PrintWriter output = new PrintWriter(list.get(i));
			) {
				for (int j = 0; j < lines.size(); j++) {
					output.println(lines.get(j));
				}
			}
		}
	}

	/** Adds all Java source files in directory to list */
	public static ArrayList<File> getFiles(ArrayList<File> dir) {
		if (!dir.get(0).isDirectory()) {
			System.exit(0);
		}
		ArrayList<File> list = 
				new ArrayList<>(Arrays.asList(dir.get(0).listFiles()));
		

		filterJavaFiles(list);
		return list;
	}

	/** Removes non-Java source files from list */
	public static void filterJavaFiles(ArrayList<File> list) {
		for (int i = 0; i < list.size(); i++) {
			String str = list.get(i).getName();
			boolean isjavaCode = str.substring(str.lastIndexOf('.')).equals(".java");
			if (!isjavaCode)
				list.remove(i);
		}
	}

	/** Generates File objects and adds them to list */
	public static ArrayList<File> getDirectories(File root) {
		ArrayList<File> directories = new ArrayList<>();
		for (int i = 1; i < 34; i++) {
			directories.add(new File(root, "chapter" + i));
		}
		return directories;
	}
}

CreateFiles.java 

import java.util.*;
import java.io.*;

public class CreateFiles {
	/** Main method */
	public static void main(String[] args) throws Exception {
		// Create an ArrayList
		ArrayList<File> directories = new ArrayList<>();

		// Add directories to list
		addDirectories(directories);
		
		// Create files in each directory
		makeFiles(directories);
	}

	/** Creates and adds files to a list */
	public static void makeFiles(ArrayList<File> d) 
		throws FileNotFoundException {
		for (int i = 0; i < d.size(); i++) {
			makeFiles(3, d.get(i), "TestJavafile", ".java");
			makeFiles(2, d.get(i), "TestTextfile", ".txt");
			makeFiles(2, d.get(i), "TestDatfile", ".dat");
		}
	}

	/** Create n File objects in a directory */
	public static void makeFiles(
		int n, File dir, String fileName, String ext) 
		throws FileNotFoundException {
		for (int j = 1; j <= n; j++) {
			File file = new File(dir, fileName + j + ext);
			if(!file.exists()) {
				try (
						// Create output file
						PrintWriter output = new PrintWriter(file);
				) {
					// Write 100 integers created radomly to file
					for (int i = 0; i < 100; i++) {
						output.print(((int)(Math.random() * 500) + 1));
						output.print(" ");
					}
				}
			}
		}
	}

	/** Adds directories to a list */
	public static void addDirectories(ArrayList<File> list) {
		for (int i = 1; i <= 34; i++) {
			// Check if file exists
			File dir = new File("srcRootDirectory/chapter" + i);
			if (!dir.isDirectory()) {
				if (dir.mkdirs())
					list.add(dir);
			}
		}
	}
}