Two conditions in one if statement does the second matter if the first is false?
Okay, so I have this piece of code tested and I found there isn't any exception thrown out.
public static void main(String[] args) {
int[] list = {1,2};
if (list.length>2 && list[3] == 2){
System.out.println(list[1]);
}
}
Does the statement here
if (list.length>2 && list[3] == 2)
mean that if the first condition is false we don't even have to check the second condition?
Or it equals to
if (list.length>2){
if (list[3] == 2){
...
}
}
?
And, what if it is written in C or python or some other languages?
Thanks
It is common for languages (Java and Python are among them) to evaluate the first argument of a logical AND
and finish evaluation of the statement if the first argument is false
. This is because:
From The Order of Evaluation of Logic Operators,
When Java evaluates the expression d = b && c;, it first checks whether b is true. Here b is false, so b && c must be false regardless of whether c is or is not true, so Java doesn't bother checking the value of c.
This is known as short-circuit evaluation, and is also referred to in the Java docs.
It is common to see list.count > 0 && list[0] == "Something"
to check a list element, if it exists.
It is also worth mentioning that if (list.length>2 && list[3] == 2)
is not equal to the second case
if (list.length>2){
if (list[3] == 2){
...
}
}
if there is an else
afterwards. The else
will apply only to the if
statement to which it is attached.
To demonstrate this gotcha:
if (x.kind.equals("Human")) {
if (x.name.equals("Jordan")) {
System.out.println("Hello Jordan!");
}
} else {
System.out.println("You are not a human!");
}
will work as expected, but
if (x.kind.equals("Human") && x.name.equals("Jordan")) {
System.out.println("Hello Jordan!");
} else {
System.out.println("You are not a human!");
}
will also tell any Human who isn't Jordan
they are not human.
Yes. If the first condition is not satisfied then the remainder are not evaluated. This is known as short-circuiting. See here for more details. Note that this isn't particular to Java and lot of other languages will do the same.