Java编译器是否删除检查枚举常量的if语句？

Question

Suppose I have the following enum:

public enum BooleanEnum {
   FALSE(false), TRUE(true);
   private BooleanEnum(boolean value) {
       this.value = value;
   }
   private final boolean value;
   public boolean value() {
       return value;
   }
}

Would Java remove the following code from the compiled code?

if (BooleanEnum.FALSE.value()) {
     //would the contents here get removed?
}

I know this would be the case if I were using static final constants, for example in:

static final boolean DEBUG = false;
if (DEBUG) { x=3; }

The Java compiler would remove the if (DEBUG) { x=3; } if (DEBUG) { x=3; } code.

If the enum code above does not get removed, would there be any way to make it so without going back to static constants?

Answer 1

I assume you read already JLS #14.21 .

Would Java remove the following code from the compiled code?
if (BooleanEnum.FALSE.value()) {
//would the contents here get removed?
}

No. Because value() is not a compile time constant value. It could return true or false . See following snippet.

static enum BooleanEnum {
    FALSE(false), TRUE(true);

    private BooleanEnum(boolean value) {
        this.value = value;
    }
    private final boolean value;

    public boolean value() {
        if (System.currentTimeMillis() % 2 == 0) {
            return true;
        } else {
            return false;
        }
    }
}

The compiler does no logical analysis during the compilation. Wheras static final boolean DEBUG = false is clearly constant during the compile time and could be used for conditional compilation purpose.

If the enum code above does not get removed, would there be any way to make it so without going back to static constants?

Using static constants is the only way.

Depending what you want to achieve there could be other solutions. eg using a simple class file which is generated before the compilation based on your conditions.

public class CompileFlag {
    static final boolean DEBUG = false;
}