JAVA比较何时会得出布尔值？ 在运行时还是在编译时？

Question

In Java, When do the comparisons evaluate to boolean values? Is it at run-time or it is at compile-time? For instance, Imagine this:

int x = 6; 
if (x > 7) { doSth(); }

After the compilation will it be represented as "x > 7" in the bytecode or it will be represented as a boolean value "false"?

Answer 1

It depends on the compiler.

Some compilers will try to be clever, and where possible, evaluate expressions at compile time. Such compilers will recognise that, at the time of the if statement, x can only be 6 , and thus x < 7 will always be false. They may even remove the block that is guarded by this if statement.

However, there is no obligation for compilers to do this. A simplistic compiler may not perform any such operations, and the entire code will make its way into the bytecode despite there being no chance of it ever being executed.