刚刚开始用Java，代码难免不够简洁。

import java.math.BigDecimal;

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner cin = new Scanner(System.in);

		while (cin.hasNext()) {

			BigDecimal a = cin.nextBigDecimal();

			BigDecimal b = cin.nextBigDecimal();

			a = a.add(b);

			if (a.compareTo(BigDecimal.valueOf(0.0)) == 0) {

				System.out.println(0);

				continue;

			}

			String out = new String(a.toPlainString());

			int l = out.length();

			boolean flag = false;

			for (int i = 0; i < l; i++)

				if (out.charAt(i) == '.')

					flag = true;

			int q = l - 1;

			while (out.charAt(q) == '0')

				q--;

			if (out.charAt(q) == '.')

				q--;

			if (flag == false && out.charAt(q) != '.')

				q = l-1;

			int p = 0;

			while (out.charAt(p) == '0')

				p++;

			if (out.charAt(p) == '.')

				System.out.print(0);

			for (int i = p; i <= q; i++)

				System.out.print(out.charAt(i));

			System.out.println();

		}

		cin.close();

	}

}