spinner

import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity implements AdapterView.OnItemSelectedListener {

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

    Spinner spinner = findViewById(R.id.spinner);
    spinner.setOnItemSelectedListener(this);

    List<String> categories = new ArrayList<>();
    categories.add("Category 1");
    categories.add("Category 2");
    categories.add("Category 3");
    categories.add("Category 4");
    categories.add("Category 5");

    ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_spinner_item, categories);
    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinner.setAdapter(adapter);
}

@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
    String category = parent.getItemAtPosition(position).toString();
    Toast.makeText(getApplicationContext(), "Selected Category: " + category, Toast.LENGTH_SHORT).show();
}

@Override
public void onNothingSelected(AdapterView<?> parent) {
    // Do nothing
}

}
Xmal code:

<?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">

<Spinner
    android:id="@+id/spinner"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:prompt="@string/select_category" />

</LinearLayout>