如何在Android中的EditText中阻止字符？

import android.text.InputFilter;
import android.text.Spanned;

public class BlockCharacterInputFilter implements InputFilter {

    private String blockedCharacter;

    public BlockCharacterInputFilter(String blockedCharacter) {
        this.blockedCharacter = blockedCharacter;
    }

    @Override
    public CharSequence filter(CharSequence source, int start, int end, Spanned dest, int dstart, int dend) {
        for (int i = start; i < end; i++) {
            if (source.charAt(i) == blockedCharacter.charAt(0)) {
                return "";
            }
        }
        return null;
    }
}

EditText editText = findViewById(R.id.edit_text);
InputFilter[] filters = new InputFilter[1];
filters[0] = new BlockCharacterInputFilter("0123456789"); // 阻止数字输入
editText.setFilters(filters);