Java大数应用

1.大数加法

import java.math.BigInteger;
import java.util.Scanner;


public class Main {
    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);//大数的输入，定义一个输入器
        BigInteger a = null, b = null, c = null;//开始要赋值成空
        a = BigInteger.valueOf(100);
        b = BigInteger.valueOf(99);
        int T;
        T = cin.nextInt();//读入T;
//        while(cin.hasNextBigInteger())//判断是否读到文件结尾相当于while(~scanf())
        for(int cas = 1; cas <= T; cas++)
        {
            a = cin.nextBigInteger();
            b = cin.nextBigInteger();
            
//            BigInteger zero = BigInteger.valueOf(0);//大数判断是不是等于0
//            if(a.equals(BigInteger.valueOf(0))){System.out.println("haha");}
//            if(a.equals(zero)) {System.out.println("hehe");}
            c = a.add(b);
            if(cas > 1) System.out.println();//大数的换行输出
            System.out.println("Case " + cas + ":");//大数的输出是用+号连接
            System.out.println(a + " + " + b + " = "+c);
        }
        cin.close();//关闭读入器
    }

}

2.大实数

import java.math.BigDecimal;
import java.util.Scanner;


public class Main {
    public static void main(String[] args) {
    Scanner s = new Scanner(System.in);
    while(s.hasNext()){
        BigDecimal b = s.nextBigDecimal();
        BigDecimal ans = BigDecimal.valueOf(1);
        int n = s.nextInt();
        while(n-- > 0)
            ans = ans.multiply(b);
        String string = ans.stripTrailingZeros().toPlainString().toString();
        if(string.startsWith("0."))
            string = string.substring(1);
        System.out.println(string);
    }
        s.close();
    }
}