Any difference between the two expressions?

Question

int p=4,u=12;

System.out.println(p=u);
System.out.println(p=+u);

I don’t understand the difference between the two expressions?

Answer 1

In the first impression there is only one assignment the p receives the value of u

int p=4,u=12;
System.out.println(p=u);
Resultado: 12

In Second Impression there is an attribute but you make use of the unary operator + on the operand u:

int p=4,u=12;
System.out.println(p=+u); //é o mesmo que p = +(u) OU p = 1(u)
Resultado: 12

With the above values it is difficult to notice the difference, but in the example below note the change:

int p=4,u=-12;
System.out.println(p=-u); //é o mesmo que p = -(u) OU p = -1(u)
Resultado: 12

Here is a short explanation of the unary operator:

a = -b;

In the above example b is the operand over which the operator - acts.

Answer 2

In theory it is quite different. One makes an assignment of a value contained in a variable to another variable. The other operates the value of a variable stating that it wants to apply a positive to it.

In practice it is the same thing. When one uses the operator of "more" unary (which is different from the binary where one makes a sum), it is innocuous.

Do you remember math class? Positive with positive gives positive, positive with negative gives negative, that is, in this case it will always give the very value that it is being applied.

It is certain (I doubt that any compiler works differently) that the language will make the + a null operation and in execution there is no instruction that does anything because of the unary operator, then the performance will be the same.

Some say that languages should not even have this operator since it does not do something useful. Some say that it can give a better semantics to the intended, even if it does not change the result.

The unary operator of negative already influences, since if the value is negative it becomes positive, according to the same math class.

It is not recommended to use something that has side effect like expression. And this code does this. It calculates and assigns a value and already uses it as an argument of the method that will make the impression. This code would be better written as:

int p = 4, u = 12;
p = u;
System.out.println(p);
p = +u;
System.out.println(p);

I put in the Github for future reference.

But it depends on the context. In this example I wouldn’t even need it. In some I see no problem using attribution as an expression.

Nor will I enter into the question having a syntax error and the intention was to do something else.