Java 逻辑运算符短路
Which set is short-circuiting, and what exactly does it mean that the complex conditional expression is short-circuiting?
public static void main(String[] args) {
int x, y, z;
x = 10;
y = 20;
z = 30;
// T T
// T F
// F T
// F F
//SET A
boolean a = (x < z) && (x == x);
boolean b = (x < z) && (x == z);
boolean c = (x == z) && (x < z);
boolean d = (x == z) && (x > z);
//SET B
boolean aa = (x < z) & (x == x);
boolean bb = (x < z) & (x == z);
boolean cc = (x == z) & (x < z);
boolean dd = (x == z) & (x > z);
}
解决方案
The &&
and ||
operators "short-circuit", meaning they don't evaluate the right-hand side if it isn't necessary.
The &
and |
operators, when used as logical operators, always evaluate both sides.
There is only one case of short-circuiting for each operator, and they are:
false && ...
- it is not necessary to know what the right-hand side is because the result can only befalse
regardless of the value theretrue || ...
- it is not necessary to know what the right-hand side is because the result can only betrue
regardless of the value there
Let's compare the behaviour in a simple example:
public boolean longerThan(String input, int length) {
return input != null && input.length() > length;
}
public boolean longerThan(String input, int length) {
return input != null & input.length() > length;
}
The 2nd version uses the non-short-circuiting operator &
and will throw a NullPointerException
if input
is null
, but the 1st version will return false
without an exception.
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