How to parse a double from EditText to TextView? (

Question

I'm realy beginning to learn Java. When I run this code everything works fine till I leave my EditText boxes in the from empty and hit the run button. Then I get:

ERROR/AndroidRuntime(866): FATAL EXCEPTION: main
ERROR/AndroidRuntime(866): java.lang.NumberFormatException: 
ERROR/AndroidRuntime(866):     at org.apache.harmony.luni.util.FloatingPointParser.parseDouble(FloatingPointParser.java:267)

I guess when I try to parse a Double from string it doesn't get any value and creates an error. I was wondering how to avoid this error and give some kind of a value to the variable so it is never empty? Thanks for all the help!

import android.app.Activity;
import android.os.Bundle;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Button;
import android.view.View;
import android.view.View.OnClickListener;

public class Main extends Activity {

    private EditText noKids;
    private EditText noGumballs;
    private TextView noSum;
    private Button b;
    private Button br;
    double etKids = 0;
    double etGumballs = 0;
    private double tvSumIn = 0.00;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        initControls();
    }


    private void initControls() {
        noKids = (EditText) findViewById(R.id.xetKids);
        noGumballs = (EditText) findViewById(R.id.xetGumballs);
        noSum = (TextView) findViewById(R.id.tvSum);


        br = (Button) findViewById(R.id.xbtnReset);
        br.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                reset();
                br.setVisibility(View.INVISIBLE);
            }

            private void reset() {
                noKids.setText("");
                noGumballs.setText("");
                noSum.setText("");

            }

        });

        b = (Button) findViewById(R.id.xbtnCalculate);
        b.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {               
                calculate();
                br.setVisibility(View.VISIBLE);
                }

        private void calculate() {

            etKids = Double.parseDouble(noKids.getText().toString());
            etGumballs = Double.parseDouble(noGumballs.getText().toString());
            tvSumIn = etGumballs / etKids; 
            String thisIsIt = new Double(tvSumIn).toString();

            if(tvSumIn < 2){
                noSum.setText(thisIsIt + " This is it ");
            }else{
                noSum.setText("This is else");
            }

        }

        });



        }
    }

This is my main.xml file and I'm guessing there's nothing special to put into manifest.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <TextView android:id="@+id/textView1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="How many kids have you got?"></TextView>
    <EditText android:layout_width="match_parent" android:layout_height="wrap_content" android:inputType="number" android:id="@+id/xetKids">
        <requestFocus></requestFocus>
    </EditText>
    <TextView android:id="@+id/textView2" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="How many gumballs have you got?"></TextView>
    <EditText android:layout_width="match_parent" android:layout_height="wrap_content" android:inputType="number" android:id="@+id/xetGumballs"></EditText>
    <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Calculate" android:id="@+id/xbtnCalculate"></Button>
    <TextView android:layout_width="match_parent" android:layout_height="wrap_content" android:id="@+id/tvSum"></TextView>
    <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/xbtnReset" android:text="Reset" android:onClick="selfDestruct" android:visibility="invisible"></Button>
</LinearLayout>

Answer 1

Another improvement:

String thisIsIt = new Double(tvSumIn).toString();

if(tvSumIn < 2){
    noSum.setText(thisIsIt + " This is it ");
}else{
    noSum.setText("This is else");
}

could be:

if(tvSumIn < 2){
    noSum.setText(tvSumIn + " This is it ");
}else{
    noSum.setText("This is else");
}

Then you don't have to create a useless String

Answer 2

Two things you can do: First, only allow numeric data in your EditText field. Actually, I see you already did that. I usually use android:numeric - this is the first I've seen of android:inputType. Thanks for that. =)

Second, ensure that you have text in your EditText with a simple check.

if(noKids.getText().length() > 0)
{
    etKids = Double.parseDouble(noKids.getText().toString());
}

Answer 3

private void calculate() {
         try{
            etKids = Double.parseDouble(noKids.getText().toString());
            etGumballs = Double.parseDouble(noGumballs.getText().toString());
            tvSumIn = etGumballs / etKids; 
          }catch(exception e)
          {
            e.printStackTrace():
          }    
        String thisIsIt = new Double(tvSumIn).toString();

            if(tvSumIn < 2){
                noSum.setText(thisIsIt + " This is it ");
            }else{
                noSum.setText("This is else");
            }

        }