在Java中使用/练习括号的最佳方法

Question

While working on Sonar static code analyzer I found some confusing (may be only to me) statement by Sonar on using parentheses.

Below are the few code snippets where Sonar says remove useless parentheses:

line>1  String auth = "Basic "+ com.somepackge.someMethod(((String) (parent.proxyUsername+ ":" + parent.proxyPassword)));
line>2  return rawtime.length() > 3 ? (rawtime.substring(0, rawtime.length() - 2) + rawtime.substring(rawtime.length() - 2, rawtime.length()).toLowerCase()) : rawtime;

though I have replaced above lines with below one to keep Sonar calm :) :

Line>3 String auth = "Basic "+ com.somepackge.someMethod((String) (parent.proxyUsername+ ":" + parent.proxyPassword));

Line>4 return  rawtime.length() > 3 ? rawtime.substring(0, rawtime.length() - 2) + rawtime.substring(rawtime.length() - 2, rawtime.length()).toLowerCase() : rawtime;

So the reason for discussing this question is:

1. Actually using braces/parentheses are way to reduce the confusion so why to remove those parentheses.

2. What is best way to use parentheses while writing any complex statement in java.

See the line>1 and Line>4 here I think

(String) (parent.proxyUsername+ ":" + parent.proxyPassword)

this part of code should have the braces to avoid confusions but what Sonar expect is something like:

   (String) parent.proxyUsername+ ":" + parent.proxyPassword

Any suggestion would be a great help. I got some links regarding this question but those were not much helpful.

Answer 1

Line 1 has redundant parentheses, but Line 2 's parentheses add clarity to the ternary statement.

Whether or not the extra parenthesis in 2 are useful is up for debate - but there's no reason not to remove the redundant ones in 1 .

Generally it's best to use extra parenthesis to convey your intent about what the code should do, or to remove ambiguity in the order that things occur.

Answer 2

There is a semantic difference between these two versions:

(String) (parent.proxyUsername+ ":" + parent.proxyPassword)

(String) parent.proxyUsername+ ":" + parent.proxyPassword

In the first, the second set of () already evaluates to a String , implicitly calling parent.proxyUsername.toString() to convert proxyUsername to a String . So the cast is redundant and should be removed IMHO. The second version casts parent.proxyUsername to String , and will throw an exception is it hasn't got runtime type String (only if it is declared a String is the cast redundant).

I agree that line 2 and 4 are complicated to read no matter if they have the redundant braces or not. Rewrite if you want clarity. That said, redundant braces are sometimes good for clarity IMHO, I do use them occasionally.

Answer 3

First snippet

String auth = "Basic "+ someMethod(((String) (parent.proxyUsername+ ":" + parent.proxyPassword)));

You could rewrite it as:

String auth = "Basic "+ someMethod(parent.proxyUsername+ ":" + parent.proxyPassword);

because the string concatenation operator already does a string conversion. Unless you want a ClassCastException thrown when proxyUsername or proxyPassword are not Strings?

Second snippet

return rawtime.length() > 3 ? (rawtime.substring(0, rawtime.length() - 2) + rawtime.substring(rawtime.length() - 2, rawtime.length()).toLowerCase()) : rawtime;

The parenthesis is indeed unnecessary but the statement is quite unreadable. If you want to keep using the ternary operator I would suggest splitting the statement across lines:

return rawtime.length() > 3
       ? rawtime.substring(0, rawtime.length() - 2) + rawtime.substring(rawtime.length() - 2, rawtime.length()).toLowerCase()
       : rawtime;

or you could revert the condition:

return rawtime.length() <= 3 ? rawtime :
       rawtime.substring(0, rawtime.length() - 2) + rawtime.substring(rawtime.length() - 2, rawtime.length()).toLowerCase();

Answer 4

the best way is to put your class that you're casting to in a parentheses then the whole part to be converted in another parentheses, then include this whole code in a container parentheses, your code should look like this eg ((String)(x+y)).

I hope that was helpful, thanks.