大数相乘（java）

mport java.util.Scanner;

02 

03public classMultiply

04{

05    publicString mul(String str1,String str2)

06    {

07        StringBuffer bstr=newStringBuffer();

08        inti=0,j=0;

09        for(i=0;i<str1.length()+str2.length();i++)

10        {

11            bstr.append('0');

12        }

13        intk=bstr.length()-1,add=0,temp=0;

14        for(j=str2.length()-1;j>=0;j--)

15        {

16            if(str2.charAt(j)!='0')

17            {

18                for(i=str1.length()-1;i>=0;i--)

19                {

20                    k=i+j+1;

21                    temp=(str2.charAt(j)-'0')*(str1.charAt(i)-'0')+(bstr.charAt(k)-'0');

22                    bstr.setCharAt(k--, (char)('0'+temp%10));

23                    add=temp/10;

24                    while(add!=0)

25                    {

26                        temp=add+bstr.charAt(k)-'0';

27                        bstr.setCharAt(k--, (char)('0'+temp%10));

28                        add=temp/10;

29                    }

30                }

31            }

32        }

33        returnbstr.substring(firstNotZeroIndex(bstr));

34    }

35     

36    privateint firstNotZeroIndex(StringBuffer str)

37    {

38        for(inti=0;i<str.length();i++)

39            if(str.charAt(i)!='0')

40                returni;

41        returnstr.length()-1;

42    }

43     

44    publicstatic void main(String[] args)

45    {

46        Multiply mul=newMultiply();

47        Scanner cin=newScanner(System.in);

48        System.out.print("请输入第一个整数：");

49        String str1=cin.next();

50        System.out.print("请输入第二个整数：");

51        String str2=cin.next();

52        System.out.print("结果是：");

53        System.out.println(mul.mul(str1, str2));

54    }

55}