java大数类

主要的整数和浮点数精度不满足要求的时候能够使用java提供的BigInteger类和BigDecimal类。

java.math.BigInteger

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java.math.BigInteger提供的方法：

1. BigInteger add(BigInteger other)
2. BigInteger subtract(BigInteger other)
3. BigInteger multiply(BigInteger other)
4. BigInteger divide(BigIntegr other)
5. int compareto(BigInteger other)
6. BigInteger mod(BigInteger other)

7. static BigInteger valueOf(long x)

   valueOf方法能够将普通的数值转换为大数值：

BigInteger a＝BigInteger.valueOf(100);

输出febonacci数列

输出febonacci数列前100项。大约在93项时会超出long的范围：

public static void  fibonacci(){
        long[] a=new long[100];
        for(int i=0;i<100;i++){
            if(i==0){
                a[0]=0;
                System.out.print(a[i]+"\t");
                continue;
            }else if(i==1){
                a[1]=1;
                System.out.print(a[i]+"\t");
                continue;
            }
            a[i]=a[i-1]+a[i-2];
            System.out.print(a[i]+"\t");
            if((i+1)%5==0){System.out.println("");}
        }
    }

改进：

public static void fibonacci() {
        BigInteger[] a = new BigInteger[200];
        for (int i = 0; i < 200; i++) {
            if (i == 0) {
                a[0] = BigInteger.valueOf(0);
                System.out.print(a[i] + "\t");
                continue;
            } else if (i == 1) {
                a[1] = BigInteger.valueOf(1);
                System.out.print(a[i] + "\t");
                continue;
            }
            a[i] = a[i - 1].add(a[i - 2]);
            System.out.println("第" + i + "项:\t" + a[i] + "\t");
        }
    }