android - Data is not getting inserted inside the Firebase Database -

i have created database in firebase , rules set are:

{   "rules": {     ".read": true,     ".write": true   } } 

the format of database like:

fieldglass-aeca7    0     age: 23     name:"shikher"    1      age: 24     name:"samarth" 

now want add record age:12 , name: xyz

i have written code in oncreate() function follows:

 protected void oncreate(bundle savedinstancestate) {   ..............  firebasedatabase.getinstance().setpersistenceenabled(true);         databasereference fg=firebasedatabase.getinstance().getreference("fieldglass-aeca7");          user u=new user(12,"shikhermishra");          string key=fg.push().getkey();         fg.child(key).setvalue(u);          try {             thread.sleep(2000);         } catch (interruptedexception e) {             e.printstacktrace();         }          fg.addlistenerforsinglevalueevent(new valueeventlistener() {             @override             public void ondatachange(datasnapshot datasnapshot) {                 log.d("listener", "the data has changed");             }              @override             public void oncancelled(databaseerror databaseerror) {              }         }); 

my user class is:

public class user {  public int age;  public string name;   public user(){  }  public user(int age,string name)  {   this.name=name;   this.age=age;  }  } 

but values not getting inserted database.and there no error reported in log well.i have used functions mentioned in https://firebase.google.com/docs/database/android/read-and-write link of firebase provided. how can insert data database?