Java 格式化输出

Question

I am not experienced in Java at all and am using a text editor to write code so I can't see what the problem is (I am running from command line) I see the error and know what it is but I have no idea how to fix it

System.out.print(String.format("%7d", Math.pow(n,2).toString()));

I also tried without the .toString() Basically if I print only n it works, but the power function gives me an error probably because of return types, but pow should return a double and the string format %7d is probably also double right?

Answer 1

You are using wrong format specifier.. %d is used for integer.

Math.pow() returns primitive double on which you cannot invoke toString() method.

Try using %7s which is for String , and convert your primitive double value to Wrapper type : -

String.format("%7s", Double.valueOf(Math.pow(n,2)).toString())

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But, you don't need to convert your argument to String , you can directly use double value with %f : -

String.format("%.3f", Math.pow(n,2));

Answer 2

You most likely want to use f instead of d without the toString . If you actually were able to do toString (as Quoi points out, you cannot do from a primitive), it would make it impossible to use Formatter s that expect the used Number object ( Double in your case).

This is the Formatter that String.format uses.

Answer 3

Math#pow(double,double) returns primitive double value you can not call toString method. Use f instead of d, and d is for a decimal integer.

 System.out.format("%7f", Math.pow(n,2));

Better start with Eclipse or any other editor to write code.

Answer 4

problem lies with toString method. You have given format specifier %7d that means integer . You can't print string in place of it.

Answer 5

The Right Format for double is %f not %d so modify your code to:

 System.out.print(String.format("%7f",  Math.pow(n,2)));

see also : link