InputFilter

InputFilters can be attached to Editables to constrain the changes that can be made to them. 

EditText edit = (EditText)findViewById(R.id.edit);

InputFilter[] FilterArray = new InputFilter[2];

FilterArray[0] = new InputFilter.LengthFilter(4); //Limit length of the text

FilterArray[1] = new InputFilter.AllCaps();   //capitalize all the lower case letters

edit.setFilters(FilterArray);