为什么这两个代码片段不同

Question

I just noticed that when I change the last line in the code fragment from potential =+ rep_pot to potential = potential + rep_pot , I get completely different behaviour. Has anybody got any idea why this is happening?

double potential = euclideanDistance(i, goal);
for (IntPoint h: hits){
    double dist = euclideanDistance(i, h);
    double a = range - dist;
    double rep_pot = (Math.exp(-1/a)) / dist;
    potential =+ rep_pot;
}

Answer 1

There is no =+ operator in Java. See the Java Language Specification for all legal operators.

=+ are two operators: = followed by + .

Answer 2

That is because

potential = potential + rep_pot

is similar to

potential += rep_pot

and

potential =+ rep_pot;

is the same as

potential = rep_pot;

Answer 3

You probably meant += . In your case it is interpreted as x = +x which is x = x

Use += :

potential += rep_pot;

Answer 4

Yes, because these two things are not equivalent.

potential =+ rep_pot;

Here we have potential assigned a value of the expression 'unary plus rep_pot'

The thing you intendet to write looks differently:

potential += rep_pot;

And this is equivalent to

potential = potential + rep_pot;