CMSC 131 (Summer 2019) Week 09 Study Questions

Question 1

Define the terms mutable and immutable.

Answer 1

The state of a mutable object may change over time. If an object is immutable, it’s state is set when it is constructed and will never vary after that.

Question 2

Are String objects mutable?

Answer 2

NO

Question 3

Are Integer objects mutable? (If you’re not sure, inspect the online API documentation for the Integer class and find out!)

Answer 3

NO

Question 4

True/False – Aliasing can lead to problems if the object is mutable.

Answer 4

True

Question 5

True/False –Aliasing can lead to problems if the object is immutable.

Answer 5

False

Question 6

Suppose you are passing (or returning) an array of primitives to/from a method. Is it safe to make a reference copy only?

Answer 6

NO

Question 7

Suppose you are passing (or returning) an array of references to immutable objects to/from a method. Is it safe to make a reference copy only? Is it safe to make a shallow copy?

Answer 7

NO, YES

Question 8

Suppose you are passing or returning an array of references to mutable objects to/from a method. Is it safe to make a reference copy only? Is it safe to make a shallow copy?

Answer 8

NO, NO

Question 9

How many ints are created by the statement: int[] a = new int[5];

Answer 9

5 ints are created – all 0.

Question 10

How many Strings are created by the statement: String[] a = new String[5]; (Hint: The answer to this question and the previous question are different!)

Answer 10

None! (Just 5 null references are created – no objects are instantiated).

Question 11

Are the elements of an array of primitives automatically initialized? If so, to what values?

Answer 11

Yes, 0

Question 12

Are the elements of an array of references to objects initialized? If so, to what values?

Answer 12

Yes, null