Checking if RadioButtons are not checked in java

I'm learning android making a simple calculator in Java like the one in the image. my calculator

When I try the app, neither of the Radio Buttons are checked, so when I press the 'calculate' button the app shuts down.

I tried making a comprobation and if neither of the buttons are checked the app shows a Toast but the app shuts down anyway.

This is the comprobation code (where btnSumar and btnRestar are the RadioButtons):

if(!btnSumar.isChecked() && !btnRestar.isChecked()) {

       Toast.makeText(MainActivity.this, "Please, select one option", Toast.LENGTH_SHORT).show();
   }

It seems logic to me, but it doesn't work.

Thanks for helping!

this is logcat

2020-09-06 18:51:48.814 10245-10245/com.triopsstudio.seccion01 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.triopsstudio.seccion01, PID: 10245
java.lang.IllegalStateException: Could not execute method for android:onClick
    at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:414)
    at android.view.View.performClick(View.java:7448)
    at android.view.View.performClickInternal(View.java:7425)
    at android.view.View.access$3600(View.java:810)
    at android.view.View$PerformClick.run(View.java:28305)
    at android.os.Handler.handleCallback(Handler.java:938)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:223)
    at android.app.ActivityThread.main(ActivityThread.java:7656)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
 Caused by: java.lang.reflect.InvocationTargetException
    at java.lang.reflect.Method.invoke(Native Method)
    at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:409)
    at android.view.View.performClick(View.java:7448) 
    at android.view.View.performClickInternal(View.java:7425) 
    at android.view.View.access$3600(View.java:810) 
    at android.view.View$PerformClick.run(View.java:28305) 
    at android.os.Handler.handleCallback(Handler.java:938) 
    at android.os.Handler.dispatchMessage(Handler.java:99) 
    at android.os.Looper.loop(Looper.java:223) 
    at android.app.ActivityThread.main(ActivityThread.java:7656) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947) 
 Caused by: java.lang.NumberFormatException: For input string: ""
    at java.lang.Integer.parseInt(Integer.java:627)
    at java.lang.Integer.parseInt(Integer.java:650)
    at com.triopsstudio.seccion01.MainActivity.Calcular(MainActivity.java:53)

You can make one of radiobutton checked by default and it's id from radioGroup

ex:

<RadioGroup
        android:id="@+id/radioSex"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" >

        <RadioButton
            android:id="@+id/radioMale"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/radio_male"
            android:checked="true" />

        <RadioButton
            android:id="@+id/radioFemale"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/radio_female" />

    </RadioGroup>

MainActivity:

//top level declaration..
private RadioGroup radioSexGroup;
private RadioButton radioSexButton;

Inside onCreate(Bundle savedInstanceState)

radioSexGroup = (RadioGroup) findViewById(R.id.radioSex);
  // get selected radio button from radioGroup
	int selectedId = radioSexGroup.getCheckedRadioButtonId();

		// find the radiobutton by returned id
  radioSexButton = (RadioButton) findViewById(selectedId);//this will have selected button id

Use the isChecked() function for every radioButton you have to check.

RadioButton maleRadioButton, femaleRadioButton;

maleRadioButton = (RadioButton) findViewById(R.id.maleRadioButton);
femaleRadioButton = (RadioButton) findViewById(R.id.femaleRadioButton);

Then use the result for your code case consideration to check radiobutton.

if (maleRadioButton.isChecked() || femaleRadioButton.isChecked()) {
     Log.d("QAOD", "Gender is Selected");
} else {
    Toast.makeText(getApplicationContext(), "Please select Gender", Toast.LENGTH_SHORT).show();
    Log.d("QAOD", "Gender is Null");
}

According to your stacktrace you have a NumberFormatException because you have no input yet. You try to parse number from empty string. Integer.parseInt("") leads to Exception ( lines 53 MainActivity class)