minimal length converter

Main.java

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.Spinner;

import java.util.Locale;

public class Main extends AppCompatActivity implements AdapterView.OnItemSelectedListener, TextWatcher {

    private EditText etTop, etBottom;
    private Spinner spin1, spin2;
    private final String UNITS[] = {"millimeters", "centimeters", "inches", "feet", "yards", "meters"};
    private final double[] VALUES = {1, 10, 25.4, 304.8, 914.3996342410972602, 1000};

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

    @Override
    public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {doConversion();}
    @Override
    public void onNothingSelected(AdapterView<?> adapterView) {}

    private void doConversion() {
        if (!etTop.getText().toString().isEmpty()) etBottom.setText(String.format(Locale.getDefault(), "%.2f", (VALUES[spin1.getSelectedItemPosition()] * Double.parseDouble("0" + etTop.getText().toString())) / (VALUES[spin2.getSelectedItemPosition()])));
        else etBottom.setText("");
    }

    @Override
    public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {doConversion();}
    @Override
    public void afterTextChanged(Editable editable) {}
    @Override
    public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {}

    private void initViews(){
        spin1 = findViewById(R.id.top_spinner);
        spin2 = findViewById(R.id.bottom_spinner);
        etTop = findViewById(R.id.et_top);
        etBottom = findViewById(R.id.et_bottom);
        etTop.addTextChangedListener(this);
    }

    private void initAdapters() {

        ArrayAdapter<String> adapter = new ArrayAdapter<>(this, R.layout.spinner_layout, UNITS);
        adapter.setDropDownViewResource(R.layout.spinner_drop);
        ArrayAdapter<String> adapter2 = new ArrayAdapter<>(this, R.layout.spinner_layout, UNITS);
        adapter2.setDropDownViewResource(R.layout.spinner_drop);
        spin1.setAdapter(adapter);
        spin2.setAdapter(adapter);

        spin1.setOnItemSelectedListener(this);
        spin2.setOnItemSelectedListener(this);
    }
}