public class Test {
    public static void main (String[] args) {
        Long a = (long) 1;
        Long b = (long) 2;
        Long c =   a   b  ;
        System.out.println(a   " "   b   " "   c);
    }
}

First I thought that there would be 3 objects (a, b, and c) but I wasn't sure if c would be an independent object which isn't dependent to a and b. Also, I'm not sure if other objects exists or not.

CodePudding user response：

Well, it depends on how you calculate it and which objects you include.

• There are three Long variables, which all have a different value eventually (2, 3 and 4 respectively). So those are three objects.

• Then there's a string concatenation expression a " " b " " c, which perhaps creates intermediate String objects.

However, if we look closely, there are many more objects:

• System.out is also an object, as well as args.

• Longs with values -128 to 127 are required to yield the same instance, as mandated by JLS § 5.1.7. This requires for some Long cache. And

  The implementation may cache these, lazily or eagerly

  So there may or may not already be 256 Long instances.

• Then Java Language Specification § 15.18.1. String Concatenation Operator says something about intermediate String objects as well:

  An implementation may choose to perform conversion and concatenation in one step to avoid creating and then discarding an intermediate String object. To increase the performance of repeated string concatenation, a Java compiler may use the StringBuffer class or a similar technique to reduce the number of intermediate String objects that are created by evaluation of an expression.

  ^{(Emphasis mine.)}

So in the end, it really depends on the actual Java implementation used.

I think questions like these are often too theoretical, and almost always answerable with "it depends". I think the exact number of objects doesn't really matter, what matters more is whether you pick the right data structures, and make your code readable.