Code written to calculate the product of two arbitrary numbers

package basic;import java.util.Scanner;import java.util.regex.Matcher;import java.util.regex.Pattern;public class Multiple {/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubtry {String[] inputstrarry = getTwoNumberInput();int[] iarray1 = changeToIntArray(inputstrarry[0]);int[] iarray2 = changeToIntArray(inputstrarry[1]);int[] iresult = multiplyTwoIntArray(iarray1, iarray2);StringBuffer sresult = new  StringBuffer();for(int i=iresult.length-1;i>=0;i--){if(i==iresult.length-1&&iresult[i]==0){}else{sresult.append(iresult[i]);}}            System.out.println("The result is: "+sresult.toString());} catch (Exception e) {System.err.println(e.getMessage());}}/* * multiplyTwoIntArray */private static int[] multiplyTwoIntArray(int[] iarray1, int[] iarray2) throws Exception{int[] iarray = null;int length1 = iarray1.length;int length2 = iarray2.length;if (iarray1 != null && length1 > 0 && iarray2 != null && length2 > 0) {iarray = new int[length1 + length2];for (int i = 0; i < length1; i++) {for (int j = 0; j < length2; j++) {int itemp = iarray[i + j] + iarray1[i] * iarray2[j];iarray[i + j] = itemp % 10;iarray[i + j + 1] += itemp / 10;if (iarray[i + j + 1] > 10) {iarray[i + j + 1] %= 10;iarray[i + j + 2]++;}}}}if(iarray==null)throw new Exception("Multiply failed!");return iarray;}/* * changeToIntArray */private static int[] changeToIntArray(String str) throws Exception {int[] iarray = null;if (str != null && str.length() > 0) {iarray = new int[str.length()];for (int i = 0; i < str.length(); i++) {iarray[str.length()-i-1] = Integer.parseInt(String.valueOf(str.charAt(i)));}} else {throw new Exception("Error in Change String to int array!");}return iarray;}/* * getTwoNumberInput */private static String[] getTwoNumberInput() throws Exception {String[] ninput = new String[2];Scanner scan = new Scanner(System.in);System.out.println("Please input two number:");String str1 = scan.next();String str2 = scan.next();if (isValidNumber(str1) && isValidNumber(str2)) {ninput[0] = str1;ninput[1] = str2;} else {throw new Exception("Input is invalid!");}return ninput;}private static boolean isValidNumber(String str) {boolean isvalid = false;Pattern p = Pattern.compile("\\d*");Matcher match = p.matcher(str);isvalid = match.matches();return isvalid;}}

In Java, two integers are multiplied. int and long are limited in size. How can we use biginteger to multiply two integers?