About Question enthuware.ocajp.i.v7.2.868 :

[baptize]

see attached photo, careful when minimum capacity is negative, this is tricky.

Just thought of sharing it with you guys.

[terence_j_coffey]

Working with java data types

StringBuffer
Notes state "If the minimum capacity argument is non positive this method takes
no action and simply returns."
I've tried this and I observe the following

If I enter StringBuffer sba = new StringBuffer(-5); it compiles fine but i get a runtime error.
Exception in thread "main" java.lang.NegativeArraySizeException
at java.lang.AbstractStringBuilder.<init>(Unknown Source)
at java.lang.StringBuilder.<init>(Unknown Source)
at InitClass3.main(InitClass3.java:54)
I'm using java 1.7.0_17
If I create a StringBuilder string with initial capacity of zero, there is no runtime error.
I've just added this in with other code but the error message is clear where the issue is.

[fasty23]

As the question asked "at least 100" (minimum), how "StringBuilder sb = new StringBuilder(100);" is correct?
Doesn't A option specified certain number of characters? or it defined the minimum number of characters and it could be more during coding?

[admin]

Because capacity of 100 satisfies what the question asks i.e. at least 100. I am not sure what is your doubt.

[fasty23]

I just assumed as the question asked "at least 100" (minimum) which means capacity 100 character is minimum and the variable could have more than 100 characters, but "StringBuilder sb = new StringBuilder(100);" has exact capacity not more.
Am I wrong?

[admin]

If you create a StringBuffer with some capacity (or even without specifying capacity), it will always be created with a certain capacity.
Creating a StringBuffer with 100 doesn't mean it can store only 100 characters. It can store more if required. But initial capacity is 100, which satisfies the requirement given in the question.

[kashyapa]

i got little bit confuse with the explanation.

The new capacity is the larger of:
The minimumCapacity argument.
Twice the old capacity, plus 2.

[admin]

Not sure what is confusing about it. You have two numbers. Just pick the larger out of those two.

[Smoljanov Sergej]

i got little bit confuse with the explanation.

The new capacity is the larger of:
The minimumCapacity argument.
Twice the old capacity, plus 2.

Code: Select all

         StringBuilder sb = new StringBuilder();
         System.out.println("new StringBuilder().capacity() = " + sb.capacity());
         //capacity of new StringBuilder() is 16
         sb.ensureCapacity(30); 
         // if current (currentCapacity*2+2)> argumetn of ensureCapacity()
         // result will be (currentCapacity*2+2)
         System.out.println(sb.capacity());
         sb = new StringBuilder();
         sb.ensureCapacity(34); 
         System.out.println(sb.capacity());
         sb = new StringBuilder();
         sb.ensureCapacity(35); 
         System.out.println(sb.capacity());
         // if current (currentCapacity*2+2)< argumetn of ensureCapacity()
         // result will be argumetn of ensureCapacity()

[gparLondon]

Great explanation @Smoljanov Sergej, thank you.

I dint get this,

Observe that the question says "at least 100 characters". In the exam, you may get a question that says "100 characters", in that case, ensureCapacity() may not be a valid option.

Why would ensureCapacity() is not a valid option when question says "100 characters"?

Thanks,
GPAR

[admin]

Because the method may allocate more than 100. Basically, you need to be careful about the wordings used in the question.

[gparLondon]

Thanks for the explanation.