TextWatcher for expiry date MM/YY automatically adding slash. For Android

ExpiryDateTextWatcher.java

import android.graphics.Canvas;
import android.graphics.Paint;
import android.support.annotation.NonNull;
import android.text.Editable;
import android.text.Spannable;
import android.text.TextWatcher;
import android.text.style.ReplacementSpan;

public class ExpiryDateTextWatcher implements TextWatcher {
    private int maxLength = 5;
    private boolean internalStopFormatFlag;

    public ExpiryDateTextWatcher() {}

    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {
    }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {
    }

    @Override
    public void afterTextChanged(Editable s) {
        if (internalStopFormatFlag) {
            return;
        }
        internalStopFormatFlag = true;
        formatExpiryDate(s, maxLength);
        internalStopFormatFlag = false;
    }

    public static void formatExpiryDate(@NonNull Editable expiryDate, int maxLength) {
        int textLength = expiryDate.length();
        // first remove any previous span
        SlashSpan[] spans = expiryDate.getSpans(0, expiryDate.length(), SlashSpan.class);
        for (int i = 0; i < spans.length; ++i) {
            expiryDate.removeSpan(spans[i]);
        }
        // then truncate to max length
        if (maxLength > 0 && textLength > maxLength - 1) {
            expiryDate.replace(maxLength, textLength, "");
            --textLength;
        }
        // finally add margin spans
        for (int i = 1; i <= ((textLength - 1) / 2); ++i) {
            int end = i * 2 + 1;
            int start = end - 1;
            SlashSpan marginSPan = new SlashSpan();
            expiryDate.setSpan(marginSPan, start, end, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
        }
    }

    public static class SlashSpan extends ReplacementSpan {
        
        public SlashSpan() {}

        @Override
        public int getSize(@NonNull Paint paint, CharSequence text, int start, int end, Paint.FontMetricsInt fm) {
            float[] widths = new float[end - start];
            float[] slashWidth = new float[1];
            paint.getTextWidths(text, start, end, widths);
            paint.getTextWidths("/", slashWidth);
            int sum = (int) slashWidth[0];
            for (int i = 0; i < widths.length; ++i) {
                sum += widths[i];
            }
            return sum;
        }

        @Override
        public void draw(@NonNull Canvas canvas, CharSequence text, int start, int end, float x, int top, int y, int bottom, @NonNull Paint paint) {
            String xtext = "/" + text.subSequence(start, end);
            canvas.drawText(xtext, 0, xtext.length(), x, y, paint);
        }
    }
}

Wants to change date format to
Dd/mm/yyyy
Then what's changes ??

@milaptank Hello Please user below class to format date,

import android.text.Editable;
import android.text.TextWatcher;
import android.util.Log;
import java.util.Calendar;
import java.util.Date;

public class DateMask implements TextWatcher {
private final static String TAG = DateMask.class.getSimpleName();
private String currentString = "";
private String separator = "/";
private DateMaskingCallback dateMaskingCallback;
private static final String INVALID_DATE_MSG = "Enter valid Date";
private static final String INVALID_MONTH_MSG = "Enter valid Month";

public DateMask(DateMaskingCallback dateMaskingCallback, String separator) {
    this.dateMaskingCallback = dateMaskingCallback;
    this.separator = separator;
}

@Override
public void beforeTextChanged(CharSequence charSequence, int start, int before, int count) {

}

@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
    try {
        String dateString = s.toString();
        Log.e(TAG, "date current string "+currentString);
        if (!currentString.equalsIgnoreCase(dateString)) {
            currentString = dateString;
            String errorString = "";
            if (dateString.length() == 2 && before == 0) {
                if (dateString.equalsIgnoreCase("00")) {
                    errorString = INVALID_MONTH_MSG;
                } else if (Integer.parseInt(dateString) < 1 || Integer.parseInt(dateString) > 12) {
                    errorString = INVALID_MONTH_MSG;
                }
            } else if (dateString.length() == 3 && before == 0) {
                String day = dateString.substring(2, dateString.length()-1);
                dateString = dateString.substring(0,2)+separator+day;
            } else if (dateString.length() == 4 && before == 0) {
                String month = dateString.substring(3, 4);
                if (Integer.parseInt(month) > 12) {
                    errorString = INVALID_DATE_MSG;
                }
            } else if (dateString.length() == 6 && before == 0) {
                String yearString = dateString.substring(3,5);
                dateString = dateString.substring(0, 3)+ yearString+separator;
                if (yearString.startsWith("0")) {
                    errorString = "Please start year with > 0";
                }
            } else if (dateString.length() >= 7 && before == 0) {
                Date currentDate = Calendar.getInstance().getTime();
                Date enteredDate = new Date(dateString);
                if (dateString.length() >= 10 && currentDate.getTime() < enteredDate.getTime()) {
                    errorString = "Future dates are not valid in dob";
                }
            }
            Log.e(TAG, "dateString "+dateString +" error String "+errorString);
            if (errorString.isEmpty()) {
               dateMaskingCallback.dateOfBirthValidation(true, dateString, errorString);
            } else {
                dateMaskingCallback.dateOfBirthValidation(false, dateString, errorString);
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

@Override
public void afterTextChanged(Editable editable) {

}

public interface DateMaskingCallback {
    void dateOfBirthValidation(final boolean isValid, final String dateOfBirth, final String error) throws Exception;
}

}

// Usage is like below
public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    
    final EditText dob = findViewById(R.id.etDob);
    dob.addTextChangedListener(new DateMask(new DateMask.DateMaskingCallback() {
        @Override
        public void dateOfBirthValidation(boolean isValid, String dateOfBirth, String error) throws Exception {
            if (isValid) {
                // sets formatted string here
                dob.setText(dateOfBirth);
                dob.setSelection(dateOfBirth.length());
            } else {
                // sets error here
                dob.setError(error);
            }
        [}](url)
    }, "/"));
}

@sumanpula thank you so much I will implement and let you know