Untitled

import java.math.BigInteger;
public class HelloWorld{
    static public int compare(BigInteger so1, BigInteger so2){	
		String str1 = so1.toString();
		String str2 = so2.toString();
		int quote = 1;
		if (str1.contains("-") && str2.contains("-")) {
		    quote = -1;
		}
		if (str1.contains("-") && !str2.contains("-"))
		    return -1;
		else if (!str1.contains("-") && str2.contains("-"))
		    return 1;
        // Calculate lengths of both string
        int n1 = str1.length(), n2 = str2.length();
        if(n1 < n2)
            return -1;
        else if(n1 > n2)
            return 1;
        else {
        	for(int i = 0; i < n1; i++) {
                if (str1.charAt(i) < str2.charAt(i))
                    return -1*quote;
                else if (str1.charAt(i) > str2.charAt(i))
                    return 1*quote;
        	}
        }
        return 0;
    }
    static public BigInteger multiply(BigInteger op1, BigInteger op2)
    {
    	String sOp1 = op1.toString();
		String sOp2 = op2.toString();
		String mark = "+";
		// check if negative
		if ((sOp1.charAt(0) == '-' || sOp2.charAt(0) == '-') &&
        (sOp1.charAt(0) != '-' || sOp2.charAt(0) != '-'))
            mark = "-";
 
        if (sOp1.charAt(0) == '-')
            sOp1 = sOp1.substring(1);
       
        if (sOp2.charAt(0) == '-')
            sOp2 = sOp2.substring(1);
        int len1 = sOp1.length();
        int len2 = sOp2.length();
     
        // will keep the result number in vector
        // in reverse order
        int result[] = new int[len1 + len2];
     
        // Below two indexes are used to
        // find positions in result.
        int i_n1 = 0;
        int i_n2 = 0;
         
        // Go from right to left in num1
        for (int i = len1 - 1; i >= 0; i--)
        {
            int carry = 0;
            int n1 = sOp1.charAt(i) - '0';
     
            // To shift position to left after every
            // multipliccharAtion of a digit in num2
            i_n2 = 0;
             
            // Go from right to left in num2            
            for (int j = len2 - 1; j >= 0; j--)
            {
                // Take current digit of second number
                int n2 = sOp2.charAt(j) - '0';
     
                // Multiply with current digit of first number
                // and add result to previously stored result
                // charAt current position.
                int sum = n1 * n2 + result[i_n1 + i_n2] + carry;
     
                // Carry for next itercharAtion
                carry = sum / 10;
     
                // Store result
                result[i_n1 + i_n2] = sum % 10;
     
                i_n2++;
            }
     
            // store carry in next cell
            if (carry > 0)
                result[i_n1 + i_n2] += carry;
     
            // To shift position to left after every
            // multipliccharAtion of a digit in num1.
            i_n1++;
        }
     
        // ignore '0's from the right
        int i = result.length - 1;
        while (i >= 0 && result[i] == 0)
        i--;

     
        // genercharAte the result String
        String str3 = "";
         
        while (i >= 0)
            str3 += (result[i--]);
        // when 1 * 0 = 0
        if (str3.length() == 0)
            return BigInteger.ZERO;
     
        BigInteger ketqua = new BigInteger(mark + str3);
	    return ketqua;
    }
     public static void main(String []args){
        BigInteger b1, b2,result,b3, b4, b5;
        b1 = new BigInteger("-5");
        b2 = new BigInteger("5");
        b3 = new BigInteger("5");
        b4 = new BigInteger("0");
        b5 = new BigInteger("11");
        System.out.println(multiply(b3,b4));
        System.out.println(b3.multiply(b2));

     }
}