不兼容的类型：在Java中使用Math.sqrt和Math.pow从Double到Int的可能松散转换

Question

I am getting the following error and i do not know why :(

Incompatible types: possible loosy conversion from double to int

It is showing on the 109th line of the code. That code uses Math.sqrt and Math.pow.

The code:

        total[b] = Math.sqrt( Math.pow( 2, ( x[b+1][b+1] - x[b][b+1] ) )  +  Math.pow( 2, ( x[b+2][b+2] - x[b][b+2] ) ) );

Please spare me if it is a simple error. I started Java just yesterday, and i am trying to get a hang of it. I am also a fairly new member of Stack Overflow :)

Here is my code:

import java.util.Scanner;

public class twoDArray4 {

public static void main(String args[])
{
    int rows;
    int columns = 3;



    Scanner scan = new Scanner(System.in);

    System.out.print("Please enter the number of cities: ");
    rows = scan.nextInt();

    double x[][] = new double [rows][columns];

    String name[] = new String[rows];

    // --- Inputting ---


    // 1st City Column Starting from 1

    for (int k = 0; k < rows; k++)
    {
        x[k][0] = (k + 1);
    }



    for (int i = 0; i < rows; i++)
    {
        System.out.println(" ");

        // Storing City Name

        System.out.print("Enter City Name: ");
        String names = scan.next();
        name[i] = names;

        // Storing Coordinates

        System.out.println("Enter coordinates for " + name[i] + " by (x [enter] y): ");

        for (int j = 1; j < columns; j++)
        {
            x[i][j] = scan.nextInt();
        }

    }

    // --- Printing --- 


    // Prints Out: cityName (x, y)


    System.out.println(" ");

    for (int i = 0; i < rows; i++)
    {
        System.out.print(" ");

        System.out.print(name[i] + " is on (");

        for (int j = 1; j < columns; j++)
        {
            if ( j > 1) 
            {
               System.out.print(", ");
            }

            System.out.print(x[i][j]);
        }

        System.out.print(")");

        System.out.println(" ");
    }


    // Prints Out Distance


    System.out.println(" ");
    System.out.println(" ");

    // Factorial Of Rows

    int z;
    int num = 1;  

    for(z = 1;z <= rows; z++)
    {    
        num = num * z;    
    }     

    int total[] = new int[num];

    // Prints Shortest Distance

    for (int b = 0; b < num; b++)
    {
        System.out.print("The shortest distance from " + name[b]);
        System.out.println(" to " + name[b+1] + " is ");     

        total[b] = Math.sqrt( Math.pow( 2, ( x[b+1][b+1] - x[b][b+1] ) )  +  Math.pow( 2, ( x[b+2][b+2] - x[b][b+2] ) ) );

    }

}

}

Answer 1

Try this instead:

total[b] = (int) (Math.sqrt( Math.pow( 2, ( x[b+1][b+1] - x[b][b+1] ) )  +  Math.pow( 2, ( x[b+2][b+2] - x[b][b+2] ) ) ) );

An integer is not as precise as a double value and you will lose precision, as stated in the error. Therefore java requires an explicit cast.

This, of course, will not solve the the loss of precision. There are cases where this is acceptable. If loss of precision is acceptable is a decision that must be made on a case to case basis by the developer. If precision must not be lost then there is no other way than assigning variables to other variables that have the same or better precision. In this case the array int[] total would have to be declared as double[] total instead.

double[] total = new double[num];

for (int b = 0; b < num; b++) {
    total[b] = Math.sqrt( Math.pow( 2, ( x[b+1][b+1] - x[b][b+1] ) )  +  Math.pow( 2, ( x[b+2][b+2] - x[b][b+2] ) ) );
}