mEdtPaymentAuthorCreditExpirationDate.addTextChangedListener(new ExpirationDateFormatWatcher());


package com.donateen.app.view;
import android.text.Editable;
import android.text.TextWatcher;

public class ExpirationDateFormatWatcher implements TextWatcher {
    private int mLength;
    @Override
    public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
        mLength = charSequence.length();
    }

    @Override
    public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
    }

    @Override
    public void afterTextChanged(Editable editable) {
        int currentLength = editable.length();
        boolean ignoreBecauseIsDeleting = false;
        if (mLength > currentLength) {
            ignoreBecauseIsDeleting = true;
        }
        if (ignoreBecauseIsDeleting) {
            return;
        }
        if (editable.length() == 2 && !editable.toString().contains("/")) {

            editable.insert(editable.length(), " / ");
        }
    }
}