MainActivity

package com.example.student.first_machlakot;

import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;

public class MainActivity extends AppCompatActivity {

    private FirebaseAuth mAuth;
    Button btn;
    EditText etMail, etPass;
    String email, password;

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

        etMail = findViewById(R.id.etMail);
        etPass = findViewById(R.id.etPass);
        btn = findViewById(R.id.btn);

        mAuth = FirebaseAuth.getInstance();

    }

    public void click(View view) {
        email = etMail.getText().toString();
        password = etPass.getText().toString();

        mAuth.createUserWithEmailAndPassword(email, password)
                .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        if (task.isSuccessful()) {
                            // Sign in success, update UI with the signed-in user's information
                            Log.d("TAGsucce", "createUserWithEmail:success");
                            FirebaseUser user = mAuth.getCurrentUser();

                        } else {
                            // If sign in fails, display a message to the user.
                            Log.w("failed", "createUserWithEmail:failure", task.getException());
                            Toast.makeText(MainActivity.this, "Authentication failed.",
                                    Toast.LENGTH_SHORT).show();
                        }


                    }
                });
    }
}