Java: How many objects are created in the code?

Question

How many objects are created in the following code?

String a, b, c;
a = "1234";
b = a;
c = a + b;

I was been told the answer is 2, because only a and b point to their own data.

c is only created from using a and b. However, isn't the act of declaring a variable considered creating it? Is this question vague? I said 3.

If I do String a;, where's the object? What if I do String a = null;? — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Nov 5, 2014 at 15:40
"However, isn't the act of declaring a variable considered creating it?" Yes, you create the variable, not the object. — m0skit0
– m0skit0, Commented Nov 5, 2014 at 16:09
you can tell your teacher the question is vague, because + operator may create two objects (1- StringBuilder, 2- String) — nafas
– nafas, Commented Nov 5, 2014 at 16:17
Also, the "1234" String might be interned, so you could even ask if it qualifies as "creating" an object ;). — phtrivier
– phtrivier, Commented Nov 5, 2014 at 16:25

Alex · Accepted Answer · 2014-11-05 16:11:27Z

3

a = "abcd" creates a String object, and initializes it with the value "abcd". So that's one object

b = a makes b point to the same spot as a, so then a + b will create a new object, which is then assigned to c. That makes a total of two objects created

answered Nov 5, 2014 at 16:11

Alex

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1 Comment

Sotirios Delimanolis Over a year ago

I do believe this is what the teacher was looking for. Students aren't meant to know at this stage that + can be implemented with StringBuilders or that a String is backed by a char[].

Peng Zhang · Accepted Answer · 2014-11-05 15:54:42Z

0

I think the answer is 2. when b=a, in fact, a has a reference to b. when you debug your program on your eclipse, you will see a and b have a same id. They are one Object actually.

answered Nov 5, 2014 at 15:54

Peng Zhang

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1 Comment

nafas Over a year ago

as @FlorentBayle have already mentioned. a + b creates another object of type StringBuilder

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