Java是否优化了2的幂除以移位?

No, the Java compiler doesn't do that, because it can't be sure on what the sign of (end - start) will be. Why does this matter? Bit shifts on negative integers yield a different result than an ordinary division. Here you can see a demo: this simple test:

System.out.println((-10) >> 1);  // prints -5
System.out.println((-11) >> 1);  // prints -6
System.out.println((-11) / 2);   // prints -5

另外请注意，我使用 >> 而不是 >>>.>>> 是无符号位移，而 >> 是有符号的.

Also note that I used >> instead of >>>. A >>> is an unsigned bitshift, while >> is signed.

System.out.println((-10) >>> 1); // prints 2147483643

@Mystical:我写了一个基准测试，表明编译器/JVM 没有进行优化:https://ideone.com/aKDShA

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