How to check if a radiobutton is checked in a radiogroup in Android?

If you want to check on just one RadioButton you can use the isChecked function

if(radioButton.isChecked())
{
  // is checked    
}
else
{
  // not checked
}

and if you have a RadioGroup you can use

if (radioGroup.getCheckedRadioButtonId() == -1)
{
  // no radio buttons are checked
}
else
{
  // one of the radio buttons is checked
}

All you need to do is use getCheckedRadioButtonId() and isChecked() method,

if(gender.getCheckedRadioButtonId()==-1)
{
    Toast.makeText(getApplicationContext(), "Please select Gender", Toast.LENGTH_SHORT).show();
}
else
{
    // get selected radio button from radioGroup
    int selectedId = gender.getCheckedRadioButtonId();
    // find the radiobutton by returned id
    selectedRadioButton = (RadioButton)findViewById(selectedId);
    Toast.makeText(getApplicationContext(), selectedRadioButton.getText().toString()+" is selected", Toast.LENGTH_SHORT).show();
}

https://developer.android.com/guide/topics/ui/controls/radiobutton.html

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 if/else case consideration.

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");
}

  rgrp.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(RadioGroup radioGroup, int i) {
            switch(i) {
                case R.id.type_car:
                    num=1;
                    Toast.makeText(getApplicationContext()," Car",Toast.LENGTH_LONG).show();
                    break;
                case R.id.type_bike:
                    num=2;
                    Toast.makeText(getApplicationContext()," Bike",Toast.LENGTH_LONG).show();
                    break;
            }
        }
    });

Try to use the method isChecked();

Like,

selectedRadioButton.isChecked() -> returns boolean.

Refere here for more details on Radio Button