Java If块具有多个语句

Question

I have a question about IF clause in Java . I have and expression:

if ((someObject != null & connectedToTheInternet) || operate) {
    // some action
}

Is my logic right: if someObject != null equals to true and connectedToTheInternet equals false then we have (someObject != null & connectedToTheInternet) equals false and then we have the following block:

if (false || operate) {
   // some action
}

And if operate equals true then // some action will be triggered?

Answer 1

Just a first note: logical AND operator is "&&" and not just "&" (bitwise AND).

Following, your answer is YES... JVM will run conditions following your thinking.

By the way, I suggest you to read something abot short-circuit of these operators: it can be interesting if you are learning.

For example if you have if (a && (b || c) and a==false , then JVM won't evaluate b or c conditions because false && ... will be always false.

The same in the case of if (a || b || c && d) : if a==true then JVM will ignore the other parts and consider it as true because true || .... true || .... will be always true.

Answer 2

Yes. if-clauses are evaluated from left to right. If no parenthesis are used, && has precedence, even higher precedence has ! (not) - similar to multiplication (AND), addition (OR) and negative numbers (-) in math (eg "A && (B || C) != A && B || C == (A && B) ||C") - I recommend to use parenthesis if you are unsure. This makes it possible to combine != null checks and calls to methods in the same if statement (eg, if (object!=null && object.dosomething()) ).

Btw. there is a difference between & and && ( short-circuit ), when & is used, the second condition gets evaluated even if the first is false already. When && is used, Java doesn't check the second condition if the first one is false as the whole term cannot be true anymore - this is only important when the second condition is not a boolean variable but a method (which gets called or not -> side effects ; this "skipping" is called short-circuit). Same for || and | where the second operator might not get evaluated if the first is already true (in case of || ).

Normally only || and && are used.

Just for completeness: & is also the bitwise AND operator in Java.

Answer 3

if (false || operate) {  
   // some action
}

If operate true then if block executing.