Java转换错误：意外类型。 必需：变量，找到：值

Question

In Java, I am trying to cast an int into a double and then back an int.

I am getting this error:

unexpected type
          (double)(result) =  Math.pow((double)(operand1),(double)(operand2));
          ^
  required: variable
  found:    value

From this code:

(double)(result) =  Math.pow((double)(operand1),(double)(operand2));
return (int)(result);

What does the error message mean?

Answer 1

You don't need to cast int to double in order to call Math.pow:

package test;

public class CastingTest {
    public static int exponent(int base, int power){
        return ((Double)Math.pow(base,power)).intValue();
    }
    public static void main(String[] arg){
        System.out.println(exponent(5,3));
    }
}

Answer 2

The message just means that you've messed up the syntax. The casting needs to go on the right hand side of the equals, not in front of the variable that you're assigning to.

Answer 3

Let's assume that result is actually a double , then you would simply only need to do...

result = Math.pow((double)(operand1),(double)(operand2));

Now, let's assume that result is actually int , then you simple need to do...

result = (int)Math.pow((double)(operand1),(double)(operand2));

Updated

With feedback from Patricia Shanahan, there is a lot of unnecessary noise in the code. Without further context, it is difficult to comment entirely, but, it is unlikely (and unhelpful) to case operand1 and operand2 explicitly to double . Java is capable of taking care of this by itself.

Math.pow(operand1, operand2);

Answer 4

This code in Java:

double my_double = 5;
(double)(result) = my_double;  

Will throw an compile time error:

The left-hand side of an assignment must be a variable

Casts are not allowed on a variable to the left of the equals sign being assigned to. It doesn't even make sense what the code would mean. Are you trying to remind the compiler that your variable is a double? As if it didn't already know?

Answer 5

you probably intend:

double result =  Math.pow((double)(operand1),(double)(operand2));
return (int)(result);

or equivalently but more simply:

double result =  Math.pow((double)operand1,(double)operand2);
return (int)result;

or even:

return (int)Math.pow((double)operand1,(double)operand2);