If a function is called using Call-by-Reference, then any changes made to the variable inside the function are affected immediately to the caller. And for Call-by-Sharing, it is affected at the end of the function.
Question 1: Does Java uses Call-by-Sharing instead of Call-by-Reference?
Question 2: I think that Call-by-Sharing differs from Call-by-Reference only while multithreading. It is created only to decrease concurrent over-writing of values while it is being used in some other thread; to provide consistency. Am I right?
I would recommend that you don't use "call by sharing" terminology. As this Wikipedia article states:
"However, the term "call by sharing" is not in common use; the terminology is inconsistent across different sources. For example, in the Java community, they say that Java is pass-by-value, whereas in the Ruby community, they say that Ruby is pass-by-reference[citation needed], even though the two languages exhibit the same semantics. Call-by-sharing implies that values in the language are based on objects rather than primitive types."
and
"Although this term has widespread usage in the Python community, identical semantics in other languages such as Java and Visual Basic are often described as call-by-value, where the value is implied to be a reference to the object."
The bottom line is that Java uses "call by sharing" ... but they don't call it that, and you probably shouldn't either if you want Java people to understand you.
I think that Call-by-Sharing differs from Call-by-Reference only while multithreading. It is created only to decrease concurrent over-writing of values while it is being used in some other thread; to provide consistency. Am I right?
No, you are not right.
"Call by sharing" really means "call by value" in the case where the value is an object reference. True "call by references" means you are (in effect) passing the address of a variable, and the called method can update the variable.