Java Testing:

public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        Main.dataTest(7351);
    }

    public static void dataTest(Integer _number) {
        if (_number != null) {
            String _numberArray = _number.toString();
            int _length = 0;
            int _sum = 0;
            int _product = 1;
            int _left = 0;
            int _right = 0;
            int _mayor = 0;
            int _menor = 0;
           
            StringBuilder invert = new StringBuilder();
           
            for (int _i = 0; _i < _numberArray.length(); _i++) {
                int data = Character.getNumericValue(_numberArray.charAt(_i));
                _sum = _sum + data;
                _product = _product * data;
               
                if (_i < 1) {
                    _left = data;
                }
               
                if (_i == _numberArray.length() - 1) {
                    _right = data;
                }

                if(_i < _numberArray.length() - 1){
                    if(Character.getNumericValue(_numberArray.charAt(_i + 1)) > _mayor){
                        _mayor = data;
                    }                   
                }

                if(_i < _numberArray.length() - 1){
                    if(Character.getNumericValue(_numberArray.charAt(_i + 1)) < Character.getNumericValue(_numberArray.charAt(_i))){
                        _menor = Character.getNumericValue(_numberArray.charAt(_i + 1));
                    }                   
                }               
                _length++;
            }
           
            for(int _j = _numberArray.length() -1; _j >=0 ; _j--){
                invert.append(_numberArray.charAt(_j));
            }
           
            System.out.println("Numero: " + _numberArray);           
            System.out.println("Cantidad de digitos: " + _length);// _numberArray.length()           
            System.out.println("Suma de sus digitos: " + _sum);
            System.out.println("Producto de sus digitos: " + _product);
            System.out.println("Digito izquierdo: " + _left);//_numberArray.charAt(0)
            System.out.println("Digito derecho: " + _right);//_numberArray.charAt(_numberArray.length() - 1)
            System.out.println("Digito mayor: " + _mayor);
            System.out.println("Digito menor: " + _menor);
            System.out.println("Número invertido: " + invert);
        }
    }
}