gistfile1.txt

    private static final String PERCENT_PATTERN = "((^[0]$)|(^[1-9]\\d*$))";
    TextWatcher mTextWatcher = new TextWatcher() {
        @Override
        public void beforeTextChanged(CharSequence charSequence, int i, int i2, int i3) {
        }

        @Override
        public void onTextChanged(CharSequence charSequence, int i, int i2, int i3) {
            if (!charSequence.toString().matches(PERCENT_PATTERN)) {
                String userInput = "" + charSequence.toString().replaceAll("[^\\d]", "");
                userInput = userInput.replaceAll("^0+(?!$)","");

                if(userInput.isEmpty()){
                    userInput = "0";
                }

                mTipView.setText(userInput);
                // keeps the cursor always to the right
                Selection.setSelection(mTipView.getText(), userInput.length());
            }
        }

        @Override
        public void afterTextChanged(Editable editable) {
        }
    };