get random value android firebase java

I want to get a random from my list by using push() in java.

Here is my code to store my data:

                Firebase publRef = f.child("Language").child("German").child("Message");
                Firebase newPublRef = publRef.push();
                Map<String, Object> publ = new HashMap<String, Object>();
                publ.put("pubMsg", writeMsgField.getText().toString());
                newPublRef.setValue(publ);

This is what it looks like in my firebase database:

Language
   German
      Message
        -Jf6ShYy7niHrqg_x4Tc: "Tomorrow is very windy"
        -Jf9v0xHAxINUUANrORU: "Today is very windy and rainy"

This is how I retrieve my data:

        Firebase f = new Firebase("http://ift.tt/1uvjcTk");             
    f.addValueEventListener(new ValueEventListener() {

        public void onDataChange(DataSnapshot snapshot) {
            disp_msg = (TextView)findViewById(R.id.display_msg);
            //disp_msg.setText(snapshot.getValue().toString());
            Iterable<DataSnapshot> ds = snapshot.getChildren();
            Iterator<DataSnapshot> ids = ds.iterator();
            Map<String, Object> newPost = (Map<String, Object>) ids.next().getValue();
            String msg = newPost.get("pubMsg").toString();
            disp_msg.setText(msg.toString());

        }

I want to retrieve a random value in my database. For example. Get random value it can either be "Tomorrow is very windy" or "Today is very windy and rainy".

Can you guys help me with some information I can use in java, I'm still inexperienced in other languages. Thank you in advance.