Calculator with single edittext field

Question

I am new to android development and I am trying to develop a calculator with single edit text field. It's not showing any compiler error but it crashes as soon as I press any button. I'm first taking the input for num1 and clearing the edit text field followed by a switch case to detect the operation and collecting the data of the second number.

public class MainActivity extends Activity implements OnClickListener{

    EditText ino;

    Button btnadd;
    Button btnsub;
    Button btnmult;
    Button btndiv;
    Button btneq;

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

        ino=(EditText) findViewById(R.id.ino);

        btnadd=(Button) findViewById(R.id.add);
        btndiv=(Button) findViewById(R.id.div);
        btnsub=(Button) findViewById(R.id.sub);
        btnmult=(Button) findViewById(R.id.mult);
        btneq=(Button) findViewById(R.id.eq);

        btnadd.setOnClickListener((OnClickListener) this);
        btnsub.setOnClickListener(this);
        btnmult.setOnClickListener(this);
        btndiv.setOnClickListener(this);

    }

    @Override
    public void onClick(View v)
    {

        float num1=0,num2=0,res=0;
        String xyz="",ans;
        num1=Float.parseFloat(ino.getText().toString());

        ino.setText(xyz);
        switch(v.getId())
        {
            case R.id.add:

                num2=Float.parseFloat(ino.getText().toString());

                res=num2+num1;

                ans=Float.toString(res);

                break;
            case R.id.div:
                num2=Float.parseFloat(ino.getText().toString());
                ino.setText(xyz);
                res=num1/num2;

                ans=Float.toString(res);
                ino.setText(ans);
                break;
            case R.id.mult:
                num2=Float.parseFloat(ino.getText().toString());
                ino.setText(xyz);
                res=num2*num1;

                ans=Float.toString(res);
                ino.setText(ans);
                break;
            case R.id.sub:
                num2=Float.parseFloat(ino.getText().toString());
                ino.setText(xyz);
                res=num1-num2;

                ans=Float.toString(res);
                ino.setText(ans);
                break;
            case R.id.eq:
                ans=Float.toString(res);
                ino.setText(ans);
                break;
            default: break;
        }



    }
}

Here is the copy of stack trace.

 12-28 00:49:52.646 2125-2125/com.example.rishabh.calculator2
 E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.rishabh.calculator2, PID: 2125
    java.lang.NumberFormatException: Invalid float: ""
        at java.lang.StringToReal.invalidReal(StringToReal.java:63)
        at java.lang.StringToReal.parseFloat(StringToReal.java:308)
        at java.lang.Float.parseFloat(Float.java:306)
        at com.example.rishabh.calculator2.MainActivity.onClick(MainActivity.java:56)
        at android.view.View.performClick(View.java:5198)
        at android.view.View$PerformClick.run(View.java:21147)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:148)
        at android.app.ActivityThread.main(ActivityThread.java:5417)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Please could you add a copy of the stacktrace you get when it crashes to the question. — Jahnold, Dec 27 '15 at 19:09
Well, you should only add check if ino.getText().toString().length > 0 — Evgeniy Strepetov, Dec 27 '15 at 19:44

Midhun MP · Answer 1 · 2015-12-27T19:37:09.760

From your code it is clear that it will throw java.lang.NumberFormatException exception. If the edit text contains invalid string or empty string the parseFloat method will throw a NumberFormatException.

You are setting the edit text value to empty string in the following code (where xyz is initialised to empty string):

ino.setText(xyz);

After that you are trying to parse the edit text data to float and it will throw an exception. You need to catch those exceptions and properly handle it in your code.

try
{
   num1=Float.parseFloat(ino.getText().toString());
}
catch (NumberFormatException e)
{
   num1 = 0.0f;
}

(Similar like this, you need to handle all the parseFloat calls)

score 0 · Answer 2 · answered Dec 27 '15 at 19:37

In your LogCat, I see the following:

java.lang.NumberFormatException: Invalid float: "" at java.lang.StringToReal.invalidReal(StringToReal.java:63)

Many times in your code you are trying to parse a String value and store it as a float, which isn't going to work:

num1=Float.parseFloat(ino.getText().toString());

Instead you should use the following to convert to String to a float:

num1 = Float.valueOf(ino.getText().toString());

score 0 · Accepted Answer · answered Dec 27 '15 at 22:41

Your code contains several problems. The first is that Float.parseFloat() will throw a java.lang.NumberFormatException if the string is empty or contains letters. This should be handled with try/catch.

The second problem is that the variables num1, num2 and res cannot be declared locally, because they will be initialized to 0.0 every time a button is clicked.

For the calculator to work it is necessary to remember the operation that is going to be performed when the user clicks the "equals"-button. The previous clicked button can be stored using an int.

The following code is tested and works.

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

public class MainActivity extends Activity implements OnClickListener {

    EditText ino;

    Button btnadd;
    Button btnsub;
    Button btnmult;
    Button btndiv;
    Button btneq;

    private float num1 = 0;
    private float num2 = 0;
    private float res = 0;

    private int operation = 0;

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

        ino=(EditText) findViewById(R.id.ino);

        btnadd=(Button) findViewById(R.id.add);
        btndiv=(Button) findViewById(R.id.div);
        btnsub=(Button) findViewById(R.id.sub);
        btnmult=(Button) findViewById(R.id.mult);
        btneq=(Button) findViewById(R.id.eq);

        btnadd.setOnClickListener(this);
        btnsub.setOnClickListener(this);
        btnmult.setOnClickListener(this);
        btndiv.setOnClickListener(this);
        btneq.setOnClickListener(this);
    }

    @Override
    public void onClick(View v)
    {
        String s = ino.getText().toString();
        try
        {
            Float.parseFloat(s);
        }
        catch (NumberFormatException e)
        {
            s = "0.0";
        }

        String xyz="",ans;
        ino.setText(xyz);

        switch(v.getId())
        {
            case R.id.eq:
                num1=Float.parseFloat(s);

                switch (operation) {
                    case R.id.add:
                        res = num2 + num1;
                        break;
                    case R.id.sub:
                        res = num2 - num1;
                        break;
                    case R.id.mult:
                        res = num2 * num1;
                        break;
                    case R.id.div:
                        res = num2 / num1;
                        break;
                    default:
                        res = 0;
                        break;
                }
                ans=Float.toString(res);
                ino.setText(ans);
                break;
        }
        num2 = Float.parseFloat(s);
        operation = v.getId();
    }
}

Calculator with single edittext field

3 Answers3