ProfileActivity.java

package com.example.pet1;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
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 ProfileActivity extends AppCompatActivity {

    private FirebaseUser user;
    private DatabaseReference reference;

    private String userID;

    private Button logout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_profile);

        logout = (Button) findViewById(R.id.singOut);

        logout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                FirebaseAuth.getInstance().signOut();
                startActivity(new Intent(ProfileActivity.this,MainActivity.class));
            }
        });

        user = FirebaseAuth.getInstance().getCurrentUser();
        reference = FirebaseDatabase.getInstance().getReference("Users");
        userID = user.getUid();
        final TextView greetingTextView = (TextView) findViewById(R.id.merhaba);
        final TextView fullNameTextView = (TextView) findViewById(R.id.fullName);
        final TextView emailTextView = (TextView) findViewById(R.id.emailAddress);
        final TextView ageTextView = (TextView) findViewById(R.id.age);
        final TextView numberTextView = (TextView) findViewById(R.id.number);
        reference.child(userID).addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                User userProfile = snapshot.getValue(User.class);

                if(userProfile != null){
                    String fullname = userProfile.fullname;
                    String email = userProfile.email;
                    String age = userProfile.age;
                    String number = userProfile.number;

                    greetingTextView.setText("Merhaba," + fullname + "!");
                    fullNameTextView.setText(fullname);
                    emailTextView.setText(email);
                    ageTextView.setText(age);
                    numberTextView.setText(number);
                }
            }
            @Override
            public void onCancelled(@NonNull DatabaseError error) {
                Toast.makeText(ProfileActivity.this,"Bir hata oluştu!",Toast.LENGTH_LONG).show();
            }
        });
    }
}