Java中不兼容的类型

Question

Should I point out that I am a begginer at this?

double averageMonthlyTemp() {
    double[] amt = new double[52];
    int sum = 0;
    int index = 0;

    for (int i = 0; i < temp.length - 1; i = i + 7) {
        //where temp is an existiing
        //previously initialized array 
        //of 365 elements, form 0 to 364
        for (int j = 0; j < 7; j++) {
            sum = sum + temp[i + j];
            if (j % 7 == 6) {
                double average = ((double) sum) / 7;
                amt[index] = average;
                index++;
                sum = (int) 0;
            }
        }
    }
    return amt;
}           

When I try to compile, I get an "incompatible types" error, with the "amt" at return amt marked in red. Does somebody know why?

Answer 1

Your method averageMonthlyTemp is specified to return some value of type double , but your amt variable is actually a double[] . Either make averageMonthlyTmp return an array of double s, or do something like this:

double averageMonthlyTmp(int month) {
...
return tmp[month]; // could be made more efficient by only calculating the temperature for one month
}

A couple of additional notes about the code:

• Because j goes from 0 to 6 inclusive, the if (j % 7 == 6) can be replaced with if (j == 6) . Also, it looks like that code (computing the average) can go directly after the second for loop.
• In your first for loop, the code will be cleaner if you replace i = i + 7 with i += 7 , which will also increase i by 7 each time.
• You don't need to put (int) before the 0 in the line sum = (int) 0; , because Java knows that when you just write 0 , you mean an int .

Answer 2

your method definition for averageMonthlyTemp says that it is supposed to return a double , that is a single value of datatype double but you are returning amt which is a double array, that is why the compiler complains. So you can either change the method definition to return an array or return a single value.

Answer 3

the returned value amt is double[] . But the function returns only a double value (not an array of double ). so try to rename the function as

double [] averagemonthlytemp()
{

}