Java 实现大整数加减乘除

自己用Java实现的大整数加减乘除运算。还有可以改进的地方，有兴趣的童鞋可以加以改进。仅供参考，请勿转载！

package barrytest;

import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

//@author Barry Wang
// all the four method have not considered the negative number yet.
// all the four method are implemented by manual calculate method.
public class BigIntegerOperation {
    public static void main(String[] age){
        String x="6465708680075747657477";
        String y="676894863054305436353";
       
        String a = add(x,y);
        System.out.println("1. x add y result is:"+a);
        String s = subtract(x,y);
        System.out.println("2. x subtract y result is:"+s);
        String m = multiply(x,y);
        System.out.println("3. x multiply y result is:"+m);
        List<String> d= divide(x,y);
        System.out.println("4. y divide x quotient is:"+d.get(0)+" reminder is:"+d.get(1));
    }

    //1. add----the method are implemented by manual calculate method.
    public static String add(String x,String y){  
        if(isNullAndNotNumber(x,y)){
            return null;
        }
       
        if(x.equals("0")){  
            return y;
        }
        if(y.equals("0")){  
            return x;
        }
          
        if(x.length()>y.length()){  
            String tmp=x;
            x=y;
            y=tmp;
        }
          
        x = addZeroToFirst(x,y.length());
        String z = addHelp(x,y);
        return z;
    }
   
    //2. subtract----the method are implemented by manual subtract calculate method.
    public static String subtract(String x, String y){
        if(isNullAndNotNumber(x,y)){
            return null;
        }
       
        if(x.equals("0")){
            return "-"+y;
        }
        if(y.equals("0")){  
            return x;
        }
       
        String sign = "";
       
        if(!isBig(x,y)){
            sign = "-";
            String tmp = x;
            x = y;
            y = tmp;
        }
       
        int len = x.length();
        int diffLen = len - y.length();
        for(int i=0; i<diffLen; i++){
            y = "0"+y;
        }
       
        int[] a = toIntArray(x);
        int[] b = toIntArray(y);
        int[] c = new int[len];
       
        int borrow = 0;
        int result = 0;
        int i = len-1;
        while(i >= 0){
            result = a[i] - b[i] + borrow;
            borrow = 0;
            if(result < 0){
                borrow = -1;
                result += 10;
            }
           
            c[i--] = result;
        }
      
        StringBuffer sb = new StringBuffer(32);
        for(int j=0; j<len; j++){
            if(c[j] == 0 && sb.length() == 0){
                continue;
            } else {
                sb.append(c[j]);
            }
        }
       
        return sign + sb.toString();
    }
   
    //3. multiply----the method are implemented by manual multiply calculate method.
    public static String multiply(String x, String y){
        if(isNullAndNotNumber(x,y)){
            return null;
        }
       
        if(x.equals("0") || y.equals("0")){
            return "0";
        }
       
        int[] a = toIntArray(x);
        int[] b = toIntArray(y);
       
        int[] temp1 = null;
        int[] temp2 = null;
       
        int enter = 0;
        int result = 0;
        int count = 1;
        for(int i=(b.length -1); i>=0; i--){
            temp1 = new int[a.length+(++count)];
            enter = 0;
            for(int j=a.length-1; j>=0; j--){
                result = a[j]*b[i]+enter;
                temp1[j+2] = result;
                enter = result/10;
            }
            temp1[1] = enter;
            temp1[0] = 0;
            temp2 = addIntArray(temp1, temp2);
        }
       
        StringBuffer sb = new StringBuffer(32);
        for(int j=0; j<temp2.length; j++){
            if(temp2[j] == 0 && sb.length() == 0){
                continue;
            } else {
                sb.append(temp2[j]);
            }
        }
       
        return sb.toString();
    }
   
    //4. divide----the method are implemented by manual divide calculate method.
    public static List<String> divide(String x, String y) {
        if(isNullAndNotNumber(x,y)){
            return null;
        }
       
        List<String> returnList = new ArrayList<String>();
        if(y.equals("0") || x.equals("0")){
            returnList.add("0");
            returnList.add("0");
            return returnList;
        }
       
        String quotient = "";//quotient
        String remainder = "";//remainder

        if (isBig(x, y) == false) {
            remainder = y;
            quotient = "0";
           
            returnList.add(quotient);
            returnList.add(remainder);
            return returnList;
        }

        int i = y.length();
        remainder = x.substring(0, i);
       
        do {
            for (int j = 9; j >= 1; j--) {
                if ((isBig(remainder, multiply(y, Integer.valueOf(j).toString())) == false) && (isBig(remainder, multiply(y, Integer.valueOf(j - 1).toString())) == true)) {
                    if((j-1) > 0){
                        quotient += (j-1);
                    }
                    remainder = subtract(remainder, multiply(y, Integer.valueOf(j-1).toString()));
                    break;
                }
            }

            int len = remainder.length();
            for (int k = 0; (k < y.length() - len) && (i < x.length()); k++) {
                remainder += x.charAt(i);
                i++;
                if (isBig(remainder, y) == false) {
                    quotient += "0";
                }
            }
            if ((isBig(remainder, y) == false) && (i < x.length())) {
                remainder += x.charAt(i);
                i++;
            }
        } while (i < x.length());

        for (int j = 9; j >= 1; j--) {
            if ((isBig(remainder, multiply(y, Integer.valueOf(j).toString())) == false) && (isBig(remainder, multiply(y, Integer.valueOf(j - 1).toString())) == true)) {
                if((j-1) > 0){
                    quotient += (j-1);
                }
                remainder = subtract(remainder, multiply(y, Integer.valueOf(j-1).toString()));
                break;
            }
        }
       
        returnList.add(quotient);
        returnList.add(remainder);
        return returnList;
    }
   
    private static boolean isNullAndNotNumber(String x, String y){
        if(x==null||y==null){
            return true;
        }
       
        if(!isNumeric(x)||!isNumeric(y)){
            return true;
        }
       
        return false;
    }
   
    //if x > y return true.
    private static boolean isBig(String x, String y){
        return (x.length() > y.length() || (x.length() == y.length() && x.compareTo(y) > 0));
    }
      
    public static String addHelp(String x,String y){  
        String z="";
        int len=x.length();
        int[] a=toIntArray(x);
        int[] b=toIntArray(y);
        int[] c=addIntArray(a, b);
       
        StringBuilder sb=new StringBuilder(32);
        for(int i=0;i<=len;i++){
            sb.append(c[i]);
        }
        if(c[0]==0){//delete the first '0' in result string
            z=sb.substring(1);
        }else{
            z=sb.toString();
        }
        return z;
    }
   
    // {2, 3, 4}+{6, 7} = {3, 0, 1}
    private static int[] addIntArray(int[] a, int b[]){
        if(a == null){
            return b;
        }
       
        if(b == null){
            return a;
        }
       
        if(a.length != b.length){//add "0" before the less length array.
            int[] temp = null;
            if(a.length < b.length){
                temp = a;
                a = b;
                b = temp;
            }
            temp = new int[a.length];
            for(int i=a.length-1, j=b.length-1; i>=0; i--){
                if(j>=0){
                    temp[i] = b[j--];
                }else{
                    temp[i] = 0;
                }
            }
            b = temp;
        }
       
       
        int len = a.length;
        int[] c=new int[len+1];
        int d=0;//to carry. No need to use int[]
        for(int i=0;i<len;i++){
            int tmpSum=a[len-1-i]+b[len-1-i]+d;
            c[len-i]=tmpSum;
            d=tmpSum/10;
        }
        c[0]=d;
       
        return c;
    }
      
 
    //String - toCharArray - toIntArray  
    public static int[] toIntArray(String str){
        int len=str.length();
        int[] result=new int[len];
        for(int i=0;i<len;i++){
            result[i]=str.charAt(i)-'0';
        }
        return result;
    }
      
    //("123",5)-->"00123"  
    public static String addZeroToFirst(String str,int length){  
        StringBuilder sb=new StringBuilder();
        int diff=length-str.length();
        while(diff>0){
            sb.append("0");
            diff--;
        }
        sb.append(str);
        return sb.toString();
    }
   
    public static boolean isNumeric(String str){  
        Pattern p=Pattern.compile("[0-9]*");
        Matcher isNum=p.matcher(str);
        return isNum.matches();
    }
}