CODEWITHSUNDEEP
javaprintfstring-formatting
Mahmoud Hanafy
Mahmoud Hanafy

Reputation: 8228

strange printf() behavior in Java

I have the following code fragment

System.out.printf("%b\n", 123);

which prints "true".

Can somebody explain this behavior? shouldn't this throw a IllegalFormatException?

Upvotes: 1

Views: 221

Answers (2)

Brian Roach
Brian Roach

Reputation: 76908

From the JavaDocs:

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".

The argument you're giving it isn't null, boolean, or Boolean, so it falls under "Otherwise" and therefore is true

Upvotes: 2

Voo
Voo

Reputation: 30226

Well since the specification says:

"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". " (src)

The behavior is quite expected isn't it? Why they decided to implement it that way - no idea, I'd agree that it's not intuitive (but well it follows C which also prints just anything if you give it the wrong arguments ;) )

Upvotes: 3

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