Android Studio project has stopped
<p>I clicked on the button number in the emulator, the app has stopped. But when I wrote the first time code and run it. There is no problem at all</p>

<p>Java Code :</p>

<pre><code>EditText e1 = (EditText)findViewById(R.id.editText);
EditText e2 = (EditText)findViewById(R.id.editText2);
TextView t1 = (TextView)findViewById(R.id.textView);
int num1 = Integer.parseInt(e1.getText().toString());
int num2 = Integer.parseInt(e2.getText().toString());
int sum = num1 + num2;
t1.setText(Integer.toString(sum));
</code></pre>