实现大位整数的加/减/乘法的java工具类

package bignumber;import java.util.*;public class BigNumUtil {public static void main(String[] args){String s1 = "1243243253";String s2 = "12656432473";System.out.println(subtraction(s1,s2));}/** * 计算两个大数相乘的方法 * @param String s1 * @param String s2 * @return String */public static String multiply(String s1,String s2){int[] bignum1 = change(s1); int[] bignum2 = change(s2); int[] demp = new int[s1.length()+s2.length()-1];for(int i=0;i<=bignum1.length-1;i++){for(int j=0;j<=bignum2.length-1;j++){demp[i+j] += bignum1[i]*bignum2[j];}}for(int i=0;i<demp.length;i++){int j = demp[i];if(j>=10){demp[i] = j%10; demp[i+1] += j/10;}}StringBuffer show = new StringBuffer("");for(int i=demp.length-1;i>=0;i--){show.append(demp[i]);}while(show.charAt(0) == '0'){show.deleteCharAt(0);}return show.toString();}/** * 计算两个大数相加的方法 * @param String s1 * @param String s2 * @return String */public static String plus(String s1,String s2){int[] bignum1 = change(s1); int[] bignum2 = change(s2); int maxLen = Math.max(s1.length(), s2.length());boolean isMax; //判定s1是否为位数较大的那个if(maxLen==s1.length()){isMax = true;}else{isMax = false;}int minLen = Math.min(s1.length(), s2.length());int[] demp = new int[maxLen+1];for(int i=0;i<=maxLen-1;i++){if(i<minLen){demp[i] += bignum1[i]+bignum2[i];}else{if(isMax){demp[i] = bignum1[i];}else{demp[i] = bignum2[i];}}}for(int i=0;i<demp.length;i++){int j = demp[i];if(j>=10){demp[i] = j%10; demp[i+1] += j/10;}}StringBuffer show = new StringBuffer("");for(int i=demp.length-1;i>=0;i--){show.append(demp[i]);}while(show.charAt(0) == '0'){show.deleteCharAt(0);}return show.toString();}/** * 计算两个大数相减的方法 * @param String s1 * @param String s2 * @return String */public static String subtraction(String s1,String s2){int[] bignum1 = change(s1); int[] bignum2 = change(s2); int maxLen = Math.max(s1.length(), s2.length());int minLen = Math.min(s1.length(), s2.length());int[] demp = new int[maxLen];boolean isPositive = true; //判定s1是否为较大的那个if(maxLen==s1.length() && maxLen!=s2.length()){isPositive = true;}else if(maxLen==s2.length() && maxLen != s1.length()){isPositive = false;}else{int i = maxLen-1;while(i>=0){if(bignum1[i]>bignum2[i]){isPositive = true;break;}else if(bignum1[i]<bignum2[i]){isPositive = false;break;}else{i--;continue;}}}StringBuffer show;if(isPositive){ //若结果数为负，计算结果前加'-'号show = new StringBuffer("");}else{show = new StringBuffer("-");}if(isPositive){//使用递归，若结果为正，正常计算；若为负，掉转顺序计算for(int i=0;i<=maxLen-1;i++){if(i<minLen){demp[i] += bignum1[i]-bignum2[i];}else{if(isPositive){demp[i] = bignum1[i];}else{demp[i] = bignum2[i];}}}for(int i=0;i<demp.length;i++){int j = demp[i];if(j<0){demp[i] = j+10; demp[i+1] -= 1;}}for(int i=demp.length-1;i>=0;i--){show.append(demp[i]);}while(show.charAt(0) == '0'){show.deleteCharAt(0);}return show.toString();}else{return "-"+subtraction(s2,s1);}}/** * 将字符串反转,并转为int数组. * @param String s * @return int[] */public static int[] change(String s){int[] result = new int[s.length()];for(int i=0;i<s.length();i++){result[i] = s.charAt(s.length() - i - 1)-'0';}return result;}}

 

BigNumUtil.java

乘法：multiply(String s1,String s2)

加法：plus(String s1,String s2)

减法：subtraction(String s1,String s2)