BigInteger测试素数循环WITHOUT isProbablePrime

In an assignment for class we have to make a loop to test for prime with a big integer WITHOUT using isProbablePrime. This is what we have.

在类的赋值中，我们必须创建一个循环来测试素数，并使用一个大整数而不使用isProbablePrime。这就是我们所拥有的。

package src.bigInteger;

import java.math.BigInteger;

public class BigIntegerTester {
    BigInteger bi = new BigInteger();

    public boolean isPrime(BigInteger number) {
        boolean result = true;
        if (number == 2) result = true;
        for (int i = 3; i <= number/2; i += 2) {
            if (number % i == 0) {result = false;}
        }
        return result;
    }
}

How can we get this to work?

我们怎样才能让它发挥作用？

1 个解决方案

#1

1. You cannot compare BigInteger using ==. You should be comparing it against another BigInteger Object using BigInteger.compareTo(BigInteger val). If you want to compare as an int, for example, you can use BigInteger.intValue().
2. 您无法使用==来比较BigInteger。您应该使用BigInteger.compareTo（BigInteger val）将其与另一个BigInteger对象进行比较。例如，如果要比较为int，则可以使用BigInteger.intValue（）。
3. You cannot perform arithmetic operations on the BigInteger Object (number/2). BigInteger has methods that will perform these operations, BigInteger.divide(BigInteger val)
4. 您不能对BigInteger对象（数字/ 2）执行算术运算。 BigInteger有一些方法可以执行这些操作，BigInteger.divide（BigInteger val）
5. Once you have established the number is a Prime, you should either break or return from the for loop.
6. 一旦你确定了数字是一个Prime，你应该从for循环中断或返回。
7. There isn't much point using BigInteger as this algorithm will not scale well. If you were to use a number too large to be held in an int, the computation time would be incredibly long.
8. 使用BigInteger并没有多大意义，因为这种算法不能很好地扩展。如果您使用的数字太大而无法保存在int中，则计算时间将非常长。
9. The second line of the isPrime(...) method, (if (number == 2) result = true;), is redundant.
10. isPrime（...）方法的第二行（if（number == 2）result = true;）是多余的。
11. Your algorithm incorrectly classifies any power of 2, where the power is greater than 1, as prime.
12. 您的算法错误地将功率大于1的2的幂幂归类为素数。
13. 1 is not prime.
14. 1不是素数。

There are many resources available that provide more efficient techniques to calculating whether an integer is a prime; you may want to give some of these a read.

有许多资源可用于提供更有效的技术来计算整数是否为素数;你可能想要给它们一些阅读。