优化：全局字符串与调用枚举类

Question

I have this enum class,

public enum Test {
    A("A"),
    B("B"),
    C("C"),
    D("D");

    private final String test;

    Test(final String test) {
        this.test = test;
    }

    public String getTestCode() {
        return stateCode;
    }
}

In a unit test class, I have declared the following global variable,

private static final String A = "A";

Question:

In the unit test class, multiple tests will use on the value of A.

For efficiency, purely from a optimization perspective (no matter how small the optimization might be), which will be more efficient

• to call the globally declared variable,

• to call the enum class the following way

   Test.A.getTestCode(); 

or does it not make any difference at all?

Answer 1

private static final String A = "A"; is compile-time constant which value will be inlined, so code like

String x = YourClass.A;

will be compiler as

String x = "A";

In case of

String x = Test.A.getTestCode();

you will need to call getTestCode() before receiving "A" .

---

You can check it using javap -c command which will allow us to see compiled version of our class. So for code like

public class Demo {

    private static final String A = "A";

    void test1(){
        String x = Demo.A;
    }

    void test2(){
        String x = "A";
    }

    void test3(){
        String x = Test.A.getTestCode();
    }

}

javap -c Demo shows

  public com.stackoverflow.Demo();
    Code:
       0: aload_0
       1: invokespecial #12                 // Method java/lang/Object."<init>":()V
       4: return

  void test1();
    Code:
       0: ldc           #8                  // String A
       2: astore_1
       3: return

  void test2();
    Code:
       0: ldc           #8                  // String A
       2: astore_1
       3: return

  void test3();
    Code:
       0: getstatic     #22                 // Field Test.A:LTest;
       3: invokevirtual #27                 // Method Test.getTestCode:()Ljava/lang/String;
       6: astore_1
       7: return

which means that methods test1 and test2 are in fact same, while test3 first needs to access A enum, then invoke its getTestCode method.

Answer 2

I'm a fan of enums because they give you more potential for expansion (like a Test.B and Test.C and other helper functions), but for clarity you may wish to maintain a class variable:

Test testA = Test.A;

And then call

testA.getTestCode();

IMO, there isn't much of a difference, though, but if you're only doing this for a single variable it's not really worth it to use an enum. If it's a value that's never changing (it seems like it is), you're probably better off with the final variable as it makes it clear that the value should never change. If you add a JavaDoc line above its declaration you can make that even clearer to anyone who is reading your code.