Does the assignment operator consume memory in Java?

Question

I have some two Strings as below:

"yes", "no".

Now, I would like to compare these Strings in two ways:

1. Directly:
   Example: "yes".equals("no")

2. By assigning the strings to some variable: Example:

   String string1 = "yes";
   String string2 ="no";
   string1.equals(string2);
   

In these two cases, is there any memory or performance difference?

Answer 1

There is a very minor difference (effectively negligible, we're talking micro-optimization here), since the string should be stored in a local variable which takes that extra bit of memory on the stack frame of the corresponding method. Whereas the constants are actually stored in the constant pool and shared. With the likely optimizations of the JVM based on the number of invocations, it won't make a difference.

Note that the bytecode would be the same if the variables were final or effectively final (assigned only once), since in this case they are treated as constants.

Answer 2

Compiling these code snippets will result in the same bytecode. Hence, there is no memory consumption or performance difference.

The assignment operator never consume memory (except the case of autoboxing: Integer number = 42). Local variable declaration may allocate memory in stack (if it necessary), but you should prefer code readability.

Answer 3

Depending on the compiler it might take the space of 2 additional object references on the stack, I guess. These are small enough you usually can ignore them unless you profiled your application and you spotted an issue there (very unlikely).

"yes".equals("no")

In real code there is hardly ever a situation like this, as you would already know if 2 literals are the same or not.