这个Java for循环终止条件是什么意思？

Question

I am wondering if anyone here knows what the termination condition in the following for loop is supposed to mean.

for (int i = 0; i < 1 << Level; i++) {
...
}

Answer 1

<< shifts the bits of the first operand n times to the left, where n is the second operand.

Therefore 1 << Level shifts the single 1 bit of the number 1 Level times to the left, which is equivalent to calculating 2 ^ Level.

So i < 1 << Level is equivalent to i < Math.pow(2,Level) .

Answer 2

Simply stated

for (int i = 0; i < 1 << Level; i++) {
...
}

is equal to

for (int i = 0; i < Math.pow(2,Level); i++) {
...
}

So the for loop will run for "Math.pow(2,Level)" times since you are counting from 0 to Math.pow(2,Level)-1.

if Level = 2 then the loop is

for(int i =0;i<4;i++){}

if Level = 3 then the loop is

for(int i =0;i<8;i++){}

if Level = 5 then the loop is

for(int i =0;i<32;i++){}

Answer 3

In addition to the other answers it might help putting parenthesis around the expression if that is unclear

for (int i = 0; i < (1 << Level); i++) {
...
}

Also since Level is a variable it is suggested to have a small letter ie level unless it is a constant, then it should be LEVEL . And I think in general that readability > performance (if it is even a problem?). So Math.pow(2,Level) is much more easy to understand if you are not a low level programmer, looks much more like Java than C.