Which of the following correctly exemplifies a Java expression for copying a variable?

Question

BlackTom AI · Accepted Answer

Let’s break down what each option is doing in terms of Java syntax and variable initialization.
Option A: double numberOfBooks = 10.5; int numberOfStudents; numberOfStudents = numberOfBooks;
- Here, numberOfBooks is a double and numberOfStudents is an int. Assigning a double to an int requires an explicit cast in Java; without a cast, this assignment is a type mismatch error. So this option is invalid as a straightforward copying expression without casting.
Option B: int numberOfBooks; int numberOfStudents; numberOfBooks = numberOfStudents;
- This copies the value from numberOfStudents into numberOfBooks. However, numberOfStudents has not been initialized when this assignment occurs. In Java, local variables must be initialized before they are read; using an uninitialized local variable here makes this code ill-formed and it will not compile. So this option is invalid due to initialization rules, not just syntax.
Option C: int numberOfBooks; int numberOfStudents = 5; numberOfBooks = numberOfStudents;
- This sequence first establishes two ints, initializes numberOfStudents to 5, and then copies that value into numberOfBooks. The assignment numberOfBooks = numberOfStudents is a valid copying expression, and no type mismatch occurs. So this option is valid as a copying expression.
Option D: int numberOfBooks; int numberOfStudents;
- This is only a declaration pair with no assignment or copying taking place. There is no copying happening, so it does not exemplify copying a variable.
In summary, you can see that A is invalid due to a type mismatch without a cast, B is invalid due to using an uninitialized variable, C demonstrates a proper copying assignment with initialized sources, and D does not copy at all. The viable example among these is the scenario shown in option C, where a value from one int variable is assigned to another after proper initialization, illustrating a proper copying operation.

Which of the following correctly exemplifies a Java expression for copying a variable?单项选择题

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