String.format（）出错

Question

Below is simple code, I got java.util.IllegalFormatConversionException whenever i == 0 .

java.util.Random r = new java.util.Random();
int i = r.nextInt(2);
String s = String.format(
    String.format("%s", i == 0 ? "%d" : "%f"),
    i == 0 ? r.nextInt() : r.nextFloat());
System.out.println(s);

The stack trace:

Exception in thread "main" java.util.IllegalFormatConversionException: d != java.lang.Float
    at java.util.Formatter$FormatSpecifier.failConversion(Formatter.java:4011)
    at java.util.Formatter$FormatSpecifier.printInteger(Formatter.java:2725)
    at java.util.Formatter$FormatSpecifier.print(Formatter.java:2677)
    at java.util.Formatter.format(Formatter.java:2449)
    at java.util.Formatter.format(Formatter.java:2383)
    at java.lang.String.format(String.java:2781)
    at hb.java.test.App.testCompiler(App.java:17)
    at hb.java.test.App.main(App.java:10)

Could someone please explain if I'm doing wrong? Thank you.

Answer 1

That is a weird one. Looks like the second conditional (i == 0 ? r.nextInt() : r.nextFloat()) is casting both to Float because of the second parameter. Never seen this before.

Here's something that works:

    public static void main(String[] args) {
        java.util.Random r = new java.util.Random();
        int i = r.nextInt(2);
        String s;
        if(i == 0){
            s = String.format("%d", r.nextInt());
        }
        else{
            s = String.format("%f", r.nextFloat());
        }
        System.out.println(s);
    }

Answer 2

i == 0 ? r.nextInt() : r.nextFloat() i == 0 ? r.nextInt() : r.nextFloat() has the type float. ?: operator cannot return both int and float .

Answer 3

How about this:

final String s;
if ( i == 0 )
{
    s = String.format("%d", r.nextInt( ));
}
else
{
    s = String.format("%f", r.nextFloat( ));
}

Answer 4

In String.format the first parameter is the format but in your example above you have the initial %s as the first parameter then %d or %f as the object to substituted for

You need to do something like this:

String s = String.format(i == 0 ? "%d" : "%f", i == 0 ? r.nextInt() : r.nextFloat());