CODEWITHSUNDEEP
javaformatting
Muhammad Gelbana
Muhammad Gelbana

Reputation: 4000

How to you use the space and sign flags when formatting an integer?

For this code

public static void main(String[] args) {
    System.out.println(String.format("%+(d", 14));
    System.out.println(String.format("%+(d", -14));
    System.out.println(String.format("% (d", 14));
    System.out.println(String.format("%+ (d", -14));
}

The output is

+14
(14)
 14
[An exception is thrown]

According to this page, as the Flags section describes, I can use the +, (i.e. space) and ( signs\flags to format integers as shown in the code above.

My questions are:

  1. Where is stated how does these flags interact with each other ?
  2. Why does the space flag work fine for the 3rd statement but throws an exception for the 4th ?
  3. For the second statement, why did the ( flag override the effect of the + flag ? Why isn't it the other way around ?

Upvotes: 0

Views: 621

Answers (1)

Andreas
Andreas

Reputation: 159106

The javadoc you referenced explicitly says:

If both the '+' and ' ' flags are given then an IllegalFormatFlagsException will be thrown.

It also lists the following restrictionm, which doesn't apply to your example:

If both the '-' and '0' flags are given then an IllegalFormatFlagsException will be thrown.

If you want to see the effect of the various flags, here is a little test program:

public static void main(String[] args) {
    test("%d");
    test("%+d");
    test("% d");
    test("%(d");
    test("%+ d");
    test("%+(d");
    test("% (d");
    test("%+ (d");
}
private static void test(String fmt) {
    try {
        System.out.printf("%5s: '" + fmt + "'%n", fmt, 14);
        System.out.printf("%5s: '" + fmt + "'%n", fmt, -14);
    } catch (Exception e) {
        System.out.printf("%5s: %s%n", fmt, e);
    }
}

Output

   %d: '14'
   %d: '-14'
  %+d: '+14'
  %+d: '-14'
  % d: ' 14'
  % d: '-14'
  %(d: '14'
  %(d: '(14)'
 %+ d: java.util.IllegalFormatFlagsException: Flags = '+ '
 %+(d: '+14'
 %+(d: '(14)'
 % (d: ' 14'
 % (d: '(14)'
%+ (d: java.util.IllegalFormatFlagsException: Flags = '+ ('

As you can see, it makes sense that '+' and ' ' are mutually exclusive. They both define how the sign of a positive number should be displayed.

Upvotes: 2

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