refactor input output stream handling

src/main/java/PasswordManager.java

@@ -7,24 +7,29 @@ import java.util.Scanner;
 public class PasswordManager implements PasswordManagerInterface {
 
     boolean running = true;
+    InputStream inputStream = System.in;
+    OutputStream outputStream = System.out;
 
     public static void main(String[] args) {
         PasswordManager pm = new PasswordManager();
-        InputStream inputStream = System.in;
-        OutputStream outputStream = System.out;
 
         while (pm.running) {
-            pm.showMenu(inputStream, outputStream);
+            pm.showMenu(null, null);
         }
         System.exit(0);
     }
 
     public PasswordManager() {
-        System.out.println("Hello World");
+        try {
+            outputStream.write("Hello World\n".getBytes(StandardCharsets.UTF_8));
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
     }
 
     @Override
     public void listVaults() {
+
     }
 
     @Override
@@ -34,6 +39,13 @@ public class PasswordManager implements PasswordManagerInterface {
 
     @Override
     public void showMenu(InputStream inputStream, OutputStream outputStream) {
+        if (inputStream == null) {
+            inputStream = this.inputStream;
+        }
+        if (outputStream == null) {
+            outputStream = this.outputStream;
+        }
+
         StringBuilder sb = new StringBuilder();
         Scanner scan = new Scanner(inputStream);
         running = true;