Formatting using printf and format

问题

In the following program

class ZiggyTest2 {

    public static void main(String[] args){     

        double x = 123.456;
        char c = 65;
        int i = 65;

        System.out.printf("%s",x);
        System.out.printf("%b",x);
        System.out.printf("%c",c);
        System.out.printf("%5.0f",x);
        System.out.printf("%d",i);
    }       
}

The output is

123.456trueA  12365

Can someone please explain how a double value (i.e. 123.456) is converted to a boolean (ie. true)

The reason I ask is because I know java does not allow numbers to be used for boolean values. For example, the following is not allowed in Java

if (5) {
 //do something
}

Thanks

回答1:

for "%b" : If the argument arg is null, then the result is "false". If arg is a boolean or Boolean, then the result is the string returned by String.valueOf(). Otherwise, the result is "true".

reference

回答2:

The API documentation seems to clearly state why.

If the argument arg is null, then the result is "false". If arg is a boolean or Boolean, then the result is the string returned by String.valueOf(). Otherwise, the result is "true".

回答3:

Because the value is of type double and this is how the %b converter works with values of this type.

来源：https://stackoverflow.com/questions/8629995/formatting-using-printf-and-format