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//Checking User Session
auth = FirebaseAuth.getInstance();
        if (auth.getCurrentUser() != null) {
            // User is logged in
        }

// Change Password
FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
 
user.updatePassword(newPassword.getText().toString().trim())
            .addOnCompleteListener(new OnCompleteListener<Void>() {
        @Override
        public void onComplete(@NonNull Task<Void> task) {
            if (task.isSuccessful()) {
                Toast.makeText(MainActivity.this, "Password is updated!", Toast.LENGTH_SHORT).show();
            } else {
                Toast.makeText(MainActivity.this, "Failed to update password!", Toast.LENGTH_SHORT).show();
                progressBar.setVisibility(View.GONE);
            }
        }
    });

// Change Email
FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
 
user.updateEmail(newEmail.getText().toString().trim())
            .addOnCompleteListener(new OnCompleteListener<Void>() {
        @Override
        public void onComplete(@NonNull Task<Void> task) {
            if (task.isSuccessful()) {
                Toast.makeText(MainActivity.this, "Email address is updated.", Toast.LENGTH_LONG).show();
            } else {
                Toast.makeText(MainActivity.this, "Failed to update email!", Toast.LENGTH_LONG).show();
            }
        }
    });
    
// Deleting Account / User
FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
if (user != null) {
        user.delete()
                .addOnCompleteListener(new OnCompleteListener<Void>() {
                    @Override
                    public void onComplete(@NonNull Task<Void> task) {
                        if (task.isSuccessful()) {
                            Toast.makeText(MainActivity.this, "Your profile is deleted:( Create a account now!", Toast.LENGTH_SHORT).show();
                        } else {
                            Toast.makeText(MainActivity.this, "Failed to delete your account!", Toast.LENGTH_SHORT).show();
                        }
                    }
                });
    }

// Sign Out
auth.signOut();
 
// this listener will be called when there is change in firebase user session
FirebaseAuth.AuthStateListener authListener = new FirebaseAuth.AuthStateListener() {
            @Override
            public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
                FirebaseUser user = firebaseAuth.getCurrentUser();
                if (user == null) {
                    // user auth state is changed - user is null
                    // launch login activity
                    startActivity(new Intent(MainActivity.this, LoginActivity.class));
                    finish();
                }
            }
        };