title: How to delete whole key data in firebase database?
body: <p>I making an app using Firebase. Structure of my data storage is- </p>
  
  <p><img src="https://i.stack.imgur.com/PDTZo.png" alt="enter image description here"></p>
  
  <p>I am calling subject and description in another activity to show them. I added a button in that activity which delete that particular key(-L6g7ttOxr... highlighted portion) data shown in Image above. I successfully got that key in second activity for particular list item to give database reference.</p>
  
  <pre><code>public void deleteCurrentMemo(){
      AlertDialog.Builder alert = new AlertDialog.Builder(
              DisplayMemo.this);
      alert.setTitle("Delete Memo");
      alert.setMessage("Are you sure you want delete current Memo?");
      Toast.makeText(this,key,Toast.LENGTH_SHORT).show();
      alert.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
          @Override
          public void onClick(DialogInterface dialog, int which) {
              mFirebaseDatabase = FirebaseDatabase.getInstance();
              mMemoDatabaseReference = mFirebaseDatabase.getReference().child("memos").child(key);
              mMemoDatabaseReference.removeValue();
              finish();
          }
      });
      alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
          @Override
          public void onClick(DialogInterface dialog, int which) {
              dialog.dismiss();
          }
      });
      alert.show();
  }
  </code></pre>
  
  <p>Above code is in second activity called on delete Button. Now how can I delete complete key data?</p>