fact

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

private EditText numberEditText;
private Button calculateButton;
private TextView resultTextView;

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

    numberEditText = findViewById(R.id.numberEditText);
    calculateButton = findViewById(R.id.calculateButton);
    resultTextView = findViewById(R.id.resultTextView);

    calculateButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            String input = numberEditText.getText().toString().trim();

            if (!input.isEmpty()) {
                int number = Integer.parseInt(input);
                long factorial = calculateFactorial(number);
                resultTextView.setText("Factorial: " + factorial);
            } else {
                resultTextView.setText("");
            }
        }
    });
}

private long calculateFactorial(int number) {
    if (number == 0 || number == 1) {
        return 1;
    } else {
        long factorial = 1;
        for (int i = 2; i <= number; i++) {
            factorial *= i;
        }
        return factorial;
    }
}

}

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:padding="16dp" tools:context=".MainActivity">

<EditText
    android:id="@+id/numberEditText"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="Enter a number"
    android:inputType="number" />

<Button
    android:id="@+id/calculateButton"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Calculate" />

<TextView
    android:id="@+id/resultTextView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:textSize="18sp"
    android:textStyle="bold"
    android:paddingTop="16dp" />

</LinearLayout>