Add a Java solution for Chapter 7.

07_trees/java/Main.java

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+import java.io.File;
+import java.util.ArrayDeque;
+import java.util.Arrays;
+import java.util.Deque;
+import java.util.List;
+
+public class Main {
+    public static void main(String[] args) {
+        // Create a File object for the "pics" directory in the current working directory
+        File file = new File(System.getProperty("user.dir"), "pics");
+
+        // Print all file names using iterative approach
+        printAllNamesFiles(file);
+
+        // Print all file names using recursive approach
+        printAllNamesFilesWithRec(file);
+    }
+
+    /**
+     * Iteratively prints the names of all files in the given directory and its subdirectories.
+     * Uses a stack (Deque) for breadth-first traversal.
+     */
+    public static void printAllNamesFiles(File dir) {
+        // Initialize the stack with all files and directories in the starting directory
+        Deque<File> filesAndDirs = new ArrayDeque<>(List.of(dir.listFiles()));
+
+        // Continue until there are no more files/directories to process
+        while (!filesAndDirs.isEmpty()) {
+            // Get the next file or directory from the stack
+            File someFileOrDir = filesAndDirs.pop();
+
+            if (someFileOrDir.isFile()) {
+                // If it is a file, print its name
+                System.out.println(someFileOrDir.getName());
+            } else if (someFileOrDir.isDirectory()){
+                // If it is a directory, add its contents to the stack
+                filesAndDirs.addAll(Arrays.asList((someFileOrDir.listFiles())));
+            }
+        }
+    }
+
+    /**
+     * Recursively prints the names of all files in the given directory and its subdirectories.
+     * Uses depth-first traversal.
+     */
+    public static void printAllNamesFilesWithRec(File dir) {
+        // Get all files and directories in the current directory
+        File[] filesAndDirs = dir.listFiles();
+
+        // Iterate through each file/directory
+        for (File someFileOrDir : filesAndDirs) {
+            if (someFileOrDir.isFile()) {
+                // If it is a file, print its name
+                System.out.println(someFileOrDir.getName());
+            } else if (someFileOrDir.isDirectory()) {
+                // If it is a directory, recursively process its contents
+                printAllNamesFilesWithRec(someFileOrDir);
+            }
+        }
+    }
+}