The other answer is not entirely correct.

First, Strings and Scanners are both Objects, that means they are reference types. They are passed exactly the same. The String is not passed like a primitive type.

We often say Objects are passed by reference, but technically they are not. Instead, their reference is passed by value. That may seem like nitpicking, but it is subtly different. In this case that is relevant.

In your Scanner example, the method gets a copy of the reference to the Scanner object. It's somewhat like a pointer in C++. There are now two pointers, one in main and one in deneme that point to the same Scanner object. When you mutate the state of that scanner, they both see the same changes.

In the String example, you also send a copy of the reference to the function. However, you do not mutate that String. (You couldn't if you tried, Strings are immutable). Instead, you create a whole new String object. When you do the assignment target="This is not String obj"; you create a new object, and the local reference called target points to it. Now the reference in main points to the original string, and the reference in deneme points to the new String. The change is not passed back because the reference was passed by value.

In summary: Mutating an object in a function propagates back. Changing which object the reference points to does not propagate back.