In android we always use RadioGroup for RadioButton and get value of the  selected radio button. check below code to know how we do this

RadioGroup radiogroup =  (RadioGroup) findViewById(R.id.groupid);
Button bt = (Button) findViewById(R.id.btnDisplay);

bt.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // get selected radio button from radioGroup
            int selectedId = radiogroup .getCheckedRadioButtonId();

            // find the radio button by returned id
            RadioButton radioButton = (RadioButton) findViewById(selectedId);

           Toast.makeText(MainActivity.this,
                radioButton.getText(), Toast.LENGTH_SHORT).show();
        }
});

You can use above code inside your onCreate method or any other method. In this first i find RadioGroup Id and after when user click on button we find Selected Radio button from group and save its id in a variable and find the selected radio button value.

🙂