java编程实现两个大数相加代码示例

public class BigIntAdd {
	private int[] array;
	//声明一个数组 
	//计算大数相加的函数 
	public static String bigAdd(BigIntAdd fisrtNum, BigIntAdd secondNum) {
		String result = "";
		Boolean falg = false;
		//判断数组是否越界的标志 
		int[] arrayOne;
		int[] arrayTwo;
		int[] arrayThree = null;
		//把较长的字符串放到arrayOne数组中，因为要把计算结果放到arrayOne数组中 
		if (fisrtNum.instance().length >= secondNum.instance().length) {
			arrayOne = fisrtNum.instance();
			arrayTwo = secondNum.instance();
		} else {
			arrayOne = secondNum.instance();
			arrayTwo = fisrtNum.instance();
		}
		for (int i = 0; i < arrayTwo.length; i++) {
			if (arrayOne[i] + arrayTwo[i] < 10) {
				//不需要进位时 
				arrayOne[i] = arrayOne[i] + arrayTwo[i];
			} else if (arrayOne[i] + arrayTwo[i] >= 10) {
				//需要进位时 
				arrayOne[i] = arrayOne[i] + arrayTwo[i] - 10;
				if ((i + 1) < arrayOne.length) {
					arrayOne[i + 1] = arrayOne[i + 1] + 1;
					//下一位的值加1
				} else {
					//当arrayOne的长度不够时要把其复制到arrayThree中 
					falg = true;
					arrayThree = new int[arrayOne.length + 1];
					System.arraycopy(arrayOne, 0, arrayThree, 0,arrayOne.length);
					arrayThree[arrayOne.length] = 1;
					//把arrayThree最高位赋值1，等价于进位的1
				}
			}
		}
		//把数组arrayThree中的元素全部的拼接为字符串 
		if (falg) {
			for (int i : arrayThree) {
				result += i;
			}
		} else {
			for (int i : arrayOne) {
				result += i;
			}
		}
		//把结果反转返回 
		return new StringBuffer(result).reverse().toString();
	}
	//初始化数组方法 
	private int[] instance() {
		return array;
	}
	//初始化构造方法 
	public BigIntAdd(String num) {
		StringBuffer sb = new StringBuffer(num);
		String string = sb.reverse().toString();
		//实现字符串反转，便于计算 
		array = new int[string.length()];
		//把字符串转化为数组 
		for (int i = 0; i < string.length(); i++) {
			array[i] = Integer.valueOf(string.substring(i, i + 1));
		}
	}
	public static void main(String [] args){
		String result=BigIntAdd.bigAdd(new BigIntAdd("5211111111"), new BigIntAdd("4099999999"));
		System.out.println(result);
	}
}