我究竟做错了什么？(What am I doing wrong? Java IllegalFormatConversionException)

我究竟做错了什么？(What am I doing wrong? Java IllegalFormatConversionException)

我有一些计算圆的属性的代码：

package circleinfo; import java.util.Scanner; public class Circleinfo { public static void main(String[] args) { Scanner input=new Scanner(System.in); int r; System.out.print("Enter the radius of the circle to find circumference, diameter, and area\n"); r = input.nextInt(); System.out.printf("The circumference is %f\n",(2*r*Math.PI)); System.out.printf("The diameter is %f\n",(r*2)); System.out.printf("The area is %f\n",(r*r*Math.PI)); } }

它计算周长，但不是其余。

Enter the radius of the circle to find circumference, diameter, and area

10

The circumference is 62.831853

Exception in thread "main" java.util.IllegalFormatConversionException: f != java.lang.Integer
    at java.util.Formatter$FormatSpecifier.failConversion(Formatter.java:4045)
    at java.util.Formatter$FormatSpecifier.printFloat(Formatter.java:2761)
    at java.util.Formatter$FormatSpecifier.print(Formatter.java:2708)
    at java.util.Formatter.format(Formatter.java:2488)
    at java.io.PrintStream.format(PrintStream.java:970)
    at java.io.PrintStream.printf(PrintStream.java:871)
    at circleinfo.Circleinfo.main(Circleinfo.java:30)
The diameter is Java Result: 1
I have some code for calculating properties of a circle:
 
package circleinfo;

import java.util.Scanner;

public class Circleinfo {

    public static void main(String[] args) {

        Scanner input=new Scanner(System.in);
        int r;

        System.out.print("Enter the radius of the circle to find circumference, diameter, and area\n");

        r = input.nextInt();

        System.out.printf("The circumference is %f\n",(2*r*Math.PI));
        System.out.printf("The diameter is %f\n",(r*2));
        System.out.printf("The area is %f\n",(r*r*Math.PI));

    }
}
 
It calculates circumference, but not the rest. 
 
Enter the radius of the circle to find circumference, diameter, and area

10

The circumference is 62.831853

Exception in thread "main" java.util.IllegalFormatConversionException: f != java.lang.Integer
    at java.util.Formatter$FormatSpecifier.failConversion(Formatter.java:4045)
    at java.util.Formatter$FormatSpecifier.printFloat(Formatter.java:2761)
    at java.util.Formatter$FormatSpecifier.print(Formatter.java:2708)
    at java.util.Formatter.format(Formatter.java:2488)
    at java.io.PrintStream.format(PrintStream.java:970)
    at java.io.PrintStream.printf(PrintStream.java:871)
    at circleinfo.Circleinfo.main(Circleinfo.java:30)
The diameter is Java Result: 1

                
最满意答案
                
                    
                        
 r是一个int ，所以r*2也是一个int ，这意味着在第二个打印语句中不能使用%f 。 改为尝试%d 。 
 
 回想一下， %f是浮点数，而%d是整数。 这在Formatter的文档中进行了概述（请参阅格式字符串语法 ）。 
r is an int, so r*2 is also an int, meaning that in your second print statement %f cannot be used. Try %d there instead.
 
Recall that %f is for floating point numbers while %d is for integers. This is outlined in the documentation of Formatter (see Format String Syntax).