Enthuware

The 3rd option given to this question is:

Long.longValue(mStr);

The Exam editor's note on this option is:

longValue is a non-static method in Long class.

My question is what prevents us from using a non- static method
in this context?

It is not clear what are you trying to do. Option 3 will not compile because of the reason given. Please post exact code that you think should work.

Maybe a more precise explanation to the 3rd option could be:
the signature of longValue() method does not take a String as a parameter

public long longValue()
Returns the value of this Long as a long value.
Specified by:
longValue in class Number
Returns:
the numeric value represented by this object after conversion to type long.

Hi All,

I have a question in related to this question when it comes to equality. And I was looking into the static method valueOf of Integer. And while I was experimenting that this returns true.

Integer bl = Integer.valueOf(123);
Integer bl2 = Integer.valueOf(123);
System.out.println( bl == bl2 ); // => false

valueOf method


Isn't this supposed to return since both are returning an instance of Integer ?

Thanks

It does print true. Not sure how are you running it but always use command line.
-Paul.

Hi Paul,

Yes, you are right it does return - true -, The comment is what I expected to get, but printed true. However, upon further investigation and experiment I realised that if the value of int is less than 127 the JVM behaves differently. Where it uses, some sort of Cached data.

For example the following code returns false because is more than 127:

Integer a = Integer.valueOf(129);
Integer b = Integer.valueOf(129);
System.out.println( a == b ); // => false

and this is true:

Integer a = Integer.valueOf(123);
Integer b = Integer.valueOf(123);
System.out.println( a == b );

- Thanks

That is correct. The idea is to not create multiple Integer objects for values between -128 to 127.
See this: http://stackoverflow.com/questions/3131 ... ng-in-java

Could anybody clarify about 3rd option

Long.longValue(mStr);

why it's not correct in this question?

Given:
String mStr = "123";
long m = // 1
Which of the following options when put at //1 will assign 123 to m?

I've tried to compile that code and it's runned without any problem.

Are you sure you tried the correct code because it doesn't compile.
Use command line to test: https://enthuware.com/oca-ocp-java-cert ... cation-ide

Oh, sorry, I confused and wrote in my code "Long.valueOf(mStr)" instead of "Long.longValue(mStr)". Thanks for helping!

Didn't expect that we need to know about longValue() method as well. Is knowing valueOf() and parseLong() only adequate for the exam?

You need to know about all variants that create wrapper objects.

Some explaination could be added to Option B: " Long.parseLong(mStr);".