final EditText[] editTextArray = new EditText[] {
                    (EditText) findViewById(R.id.num1),
                    (EditText) findViewById(R.id.num2),
                    (EditText) findViewById(R.id.num3),
                    (EditText) findViewById(R.id.num4),
                    (EditText) findViewById(R.id.num5),
                    (EditText) findViewById(R.id.num6),
                    (EditText) findViewById(R.id.num7),
                    (EditText) findViewById(R.id.num8),
                    (EditText) findViewById(R.id.num9),
                    (EditText) findViewById(R.id.num10),
                    (EditText) findViewById(R.id.num11),
                    (EditText) findViewById(R.id.num12),
                    (EditText) findViewById(R.id.num13),
                    (EditText) findViewById(R.id.num14),
                    (EditText) findViewById(R.id.num15),
                    (EditText) findViewById(R.id.num16),
            };

for (EditText anEditTextArray : editTextArray) {
                checkTextInput(anEditTextArray);
            }

private boolean checkTextInput(EditText input) {

    String inputNum = input.getText().toString();

    if (inputNum.isEmpty()){

        // Toast message
        Toast.makeText(MainActivity.this, "The board is missing numbers.", Toast.LENGTH_SHORT).show();
        return true;

    } else {

        Log.i(TAG, "working");
        return false;
    }

} // end checkTextInput