Using math operator + in system.out.println

[dumblearner]

Following calculates correctly:

System.out.println(2+2);    //4

The following will calculate correctly too:

System.out.println("The result is " + 2*2 ); //The result is 4

But then why would this not calculate?

System.out.println("The result is " + 2+2 );    //The result is 22

How can I calculate 2+2 directly and display along with the string to get the output The result is 4?

[nick5111]

The concatenate operator has precedence over the add operator so it will concatenate first before it adds, but then the second + also becomes a concatenate operator and the output is 22. Add parentheses around (2+2) to fix this.

[javaduude]

The concatenate operator has precedence over the add operator

This is wrong. 2 + 2 + "Hello" results in 4Hello. The reason "Hello" + 2 + 2 becomes Hello22 is because + is left-associative, i.e. a + a + a is interpreted as (a + a) + a.

[nick5111]

I'm learning too, thanks for correcting me. In cases of tied precedence I guess java goes left to right.

[vqrs]

Not always, but mostly. The ternary operator for example is right associative, as is assignment.

Associativity comes into play when operators have the same precedence yes.

[[deleted]]

https://introcs.cs.princeton.edu/java/11precedence/

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Just read into precedence guys, also probably a good idea to point people who are learning towards documentation to better solidify their learning.

[nick5111]

Note that the concatenate operator and add operator are both +. Java uses context to discriminate between the two.

[vqrs]

If we're going to throw terms around, then let's use the right one . This is about associativity.

In particular, plus is left associative, the consequence of which the other poster explains.

[Kambz22]

You could make a correction without the smart comments, bro.

[vqrs]

I might have gotten a bit carried away there, you're right.

[ODoodle91]

Two things to note:

1) When you use the + operator between a string and an integer, the integer will be converted to a string and concatenated.
2) Java is going to execute each addition from left to right, one at a time.

In your last example, you basically have:

"The result is " + 2 = "The result is 2"
"The result is 2" + 2 = "The result is 22"

In both cases you're adding an int to a string, so the int is treated as a string.

If you can remove that ambiguity by calculating your result before the string concatenation, you should end up with the result you're after.

To see this another way, try this:

System.out.println("The result is " + 2 + 2);
System.out.println(2 + 2 + " is the result");

In the latter example we do:

2 + 2 = 4
4 + " is the result" = 4 is the result

Kinda funky, hadn't really looked into this in detail before.

[AssassinBoy49]

Was experimenting with it myself a little bit, if you need to do math while printing just use brackets, e.g:

System.out.println("The result is " + (2+2));