Format

[Balaji Bang]

System.out.format("%1$s ", 1);

Output is 1

I thought it will expect a String parameter and gives Runtime Exception.

But for

System.out.format("%1$d ", "1");

gives error.

[Sagar Rohankar]

Banu Chowdary wrote:

System.out.format("%1$s ", 1);

Output is 1

I thought it will expect a String parameter and gives Runtime Exception.

Have you looked at format() methods signature, it takes var arg type of Object., So 1 is autoboxed in Integer type. No Exception !

Banu Chowdary wrote:
But for

System.out.format("%1$d ", "1");

gives error.

It doesn't give error, because it syntactically correct, but throws RuntimeException , stating "IllegalFormatConversionException: d != java.lang.String" , it means, you passed string and format specifier expect a Integer object or int.

[Punit Singh]

Banu remember Object class has toString() method and Integer class overrides this method.

 System.out.format("%1$s ", 1);  

so it will be converted to

 System.out.format("%1$s ", new Object[] {
            Integer.valueOf(1)
        });   

As format method takes var-args. And Integer.toString() will be used to print String.

System.out.format("%1$d ", "1");

will be converted to

  System.out.format("%1$d ", new Object[] {
            "1"
        });   

It will not run Object class does not have any method to convert String to Integer.