I'm using Java in Android studio to make a tip calculator whose values update as you change the tip percentage using a seek bar. I need the values to reset to 0 when the seek bar is zero and when the bill amount is zero. Basically, when the seekbar and bill amount are zero, so should all the other values. Also, the user should not be able to enter letters, only numbers. Could someone show me how to fix the code?

Here is my code

main activity:

package com.example.tipcalculator; import android.os.Bundle; import android.text.Editable; import android.text.TextWatcher; import android.widget.EditText; import android.widget.SeekBar; import android.widget.TextView; import androidx.appcompat.app.AppCompatActivity; public class MainActivity extends AppCompatActivity { // required components and variables private EditText bill; private TextView tv_tip1, tv_tip2, tv_tip3, tv_tipx, tv_total1, tv_total2, tv_total3, tv_totalx, seekVal; private SeekBar seekBar; private double bill_amount, tip1, tip2, tip3, tipx, total1, total2, total3, totalx, tipxper; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); // default value of seekbar is 18 tipxper = 0; // set up components bill = findViewById(R.id.bill); tv_tip1 = findViewById(R.id.tip1); tv_tip2 = findViewById(R.id.tip2); tv_tip3 = findViewById(R.id.tip3); tv_tipx = findViewById(R.id.tipx); tv_total1 = findViewById(R.id.total1); tv_total2 = findViewById(R.id.total2); tv_total3 = findViewById(R.id.total3); tv_totalx = findViewById(R.id.totalx); seekBar = findViewById(R.id.seekBar); seekVal = findViewById(R.id.seekval); // handle when text is changed bill.addTextChangedListener(new TextWatcher() { @Override public void beforeTextChanged(CharSequence s, int start, int count, int after) { } @Override public void onTextChanged(CharSequence s, int start, int before, int count) { } @Override public void afterTextChanged(Editable s) { // get the bill try { bill_amount = Double.parseDouble(bill.getText().toString()); } catch (Exception ex ){ } // change all the tip and total values updateUI(); } }); seekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() { @Override public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) { tipxper = progress; // change UI on change of seekbar updateSeekUI(); } @Override public void onStartTrackingTouch(SeekBar seekBar) { } @Override public void onStopTrackingTouch(SeekBar seekBar) { } }); } private void updateUI() { // calculate tips tip1 = Math.round(10 * bill_amount) / 100.0; tip2 = Math.round(15 * bill_amount) / 100.0; tip3 = Math.round(20 * bill_amount) / 100.0; tipx = Math.round(tipxper * bill_amount) / 100.0; tv_tip1.setText(tip1+""); tv_tip2.setText(tip2+""); tv_tip3.setText(tip3+""); tv_tipx.setText(tipx+""); // calculate total total1 = bill_amount + tip1; total2 = bill_amount + tip2; total3 = bill_amount + tip3; totalx = bill_amount + tipx; tv_total1.setText(total1+""); tv_total2.setText(total2+""); tv_total3.setText(total3+""); tv_totalx.setText(totalx+""); } private void updateSeekUI() { // update seekval seekVal.setText(tipxper + "%"); // update tip and total tipx = bill_amount * tipxper /100.0; totalx = bill_amount + tipx; tv_tipx.setText(tipx+""); tv_totalx.setText(totalx+""); } } 

activity xml: