Patterns and Regular Expressions

In Java usually validate with some specific characters, we should use Regular Expressions.

Same way in Android, here we use Patterns.

More info about the Patterns: Click here

In android EditText, we can use custom input filter to perform this.

This is for maximum input digits before and after decimal pointer.

CustomInputFilter.Java

public class CustomInputFilter implements InputFilter {
    int maxDigitsBeforeDecimalPoint;
    int maxDigitsAfterDecimalPoint;

    public CustomInputFilter(int maxDigitsBeforeDecimalPoint, int maxDigitsAfterDecimalPoint) {
        this.maxDigitsBeforeDecimalPoint = maxDigitsBeforeDecimalPoint;
        this.maxDigitsAfterDecimalPoint = maxDigitsAfterDecimalPoint;
    }

    @Override
    public CharSequence filter(CharSequence source, int start, int end, Spanned dest, int dstart, int dend) {
        StringBuilder builder = new StringBuilder(dest);
        builder.replace(dstart, dend, source
                .subSequence(start, end).toString());
        if (!builder.toString().matches(
                "[-]?(([0-9]{1})([0-9]{0," + (maxDigitsBeforeDecimalPoint - 1) + "})?)?(\\.[0-9]{0," + maxDigitsAfterDecimalPoint + "})?"

        )) {
            if (source.length() == 0)
                return dest.subSequence(dstart, dend);
            return "";
        }
        return null;
    }
}

Apply in your activity like this,
     editText.setFilters(new InputFilter[]{new CustomInputFilter(10, 2)});

For Validate Ip Address - (([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5]) or Patterns.IP_ADDRESS

For Validate File Name - ^([a-zA-Z0-9-_ ]{2,30})\.(3gp|avi|mp4)+$

For not allow the special characters - \`|\~|\!|\@|\#|\$|\%|\^|\&|\*|\(|\)|\+|\=|\[|\{|\]|\}|\||\\|\'|\<|\,|\.|\>|\?|\/|\""|\;|\:|\s

Validate Email Address = Patterns.EMAIL_ADDRESS;

Validate Phone Number =  Patterns.PHONE;