P6-P15: init

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

P7.java

@@ -0,0 +1,25 @@
+import java.io.*;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class P7 {
+    public static void main(String[] args) throws IOException {
+        String filePath = "P7.in";
+
+        List<String> lines = new ArrayList<>();
+
+        try (BufferedReader reader = new BufferedReader(new FileReader(filePath))) {
+            String line;
+            while ((line = reader.readLine()) != null)
+                lines.add(line + '\n');
+        }
+
+        Collections.sort(lines); //sort
+
+        try (BufferedWriter writer = new BufferedWriter(new FileWriter(filePath))) {
+            for (String line: lines)
+                writer.write(line);
+        }
+    }
+}