如何在不使用math.pow for java的情况下获得指数

Question

这是我的计划

// ************************************************************
    // PowersOf2.java
    //
    // Print out as many powers of 2 as the user requests
    //
    // ************************************************************

    import java.util.Scanner;

    public class PowersOf2 {

    public static void main(String[] args)

    {
        int numPowersOf2; //How many powers of 2 to compute
        int nextPowerOf2 = 1; //Current power of 2
        int exponent= 1;
        double x;

         //Exponent for current power of 2 -- this
        //also serves as a counter for the loop Scanner

        Scanner scan = new Scanner(System.in);
        System.out.println("How many powers of 2 would you like printed?");
        numPowersOf2 = scan.nextInt();
        System.out.println ("There will be " + numPowersOf2 + " powers of 2 printed");
        //initialize exponent -- the first thing printed is 2 to the what?

    while( exponent <= numPowersOf2)
        {
        double x1 = Math.pow(2, exponent);
        System.out.println("2^" + exponent + " = " + x1);
                exponent++;
        }   
//print out current power of 2
//find next power of 2 -- how do you get this from the last one?
//increment exponent

    }
}

问题是我不允许使用math.pow方法,我需要找到另一种方法来在while循环中获得正确的答案.

Answer 1

2的幂可以简单地由位移算子计算

int exponent = ...
int powerOf2 = 1 << exponent;

即使对于更一般的形式,也不应该通过"乘以n时间" 来计算指数.相反,你可以通过平方来做Exponentiation

Answer 2

如果没有性能限制，您可以执行以下操作：

double x1=1;

for(int i=1;i<=numPowersOf2;i++){
   x1 =* 2
}