method invocation 'toString' may produce 'java.lang.NullPointxception'

Question

package com.tp468.dell.automatedfishpondmonitoringsystem;

import android.os.Bundle;

import android.support.annotation.NonNull;

import android.support.v7.app.AppCompatActivity;

import android.widget.TextView;

import com.google.firebase.database.DataSnapshot;

import com.google.firebase.database.DatabaseError;

import com.google.firebase.database.DatabaseReference;

import com.google.firebase.database.FirebaseDatabase;

import com.google.firebase.database.ValueEventListener;

public class MainActivity extends AppCompatActivity {

    TextView Temperature;

    DatabaseReference dRef;

    String status;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        Temperature = (TextView)findViewById(R.id.textView);

        dRef= FirebaseDatabase.getInstance().getReference();

        dRef.addValueEventListener(new ValueEventListener() {

            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                status=dataSnapshot.child("Temperature").getValue().toString();

                Temperature.setText(status);

            }
            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });
    }
}

You need to check dataSnapshot.child("Temperature").getValue() if this expression returns a null or not.. just put up a null check in if condition before using toString on it. — Manoj Vadehra, Jan 21 '19 at 16:43
It is not an error, it is a warning generated by your IDE, because it was able to infer that there are codepaths where it might be null. — Mark Rotteveel, Jan 21 '19 at 17:52
It will showing another warning as Casting 'findViewById(R.id.textView) to 'TextView' is redundant ..Can anyone help me to resolve this warning ? — Tushar Chaudhari, Jan 23 '19 at 02:03

score 0 · Accepted Answer · answered Jan 21 '19 at 16:46

0

Try this: Use a null check first and then invoke a toString();

Object obj = dataSnapshot.child("Temperature").getValue();
if(obj!=null)
status = obj.toString();
//handle else condition too

answered Jan 21 '19 at 16:46

Manoj Vadehra

836
4
17

score 0 · Answer 2 · answered Jan 21 '19 at 17:49

Simply use the hasChild() method as a check:

@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {            
  if (dataSnapshot.hasChild("Temperature")) {
    status = dataSnapshot.child("Temperature").getValue().toString();
    Temperature.setText(status);  
  }
}

method invocation 'toString' may produce 'java.lang.NullPointxception'

2 Answers2