Since when have enum constructors’ default access modifier been private?

How long have enum constructors’ default access modifier been “private”? Since the beginning or did it change in Java 8? If it did, then what was the default access modifier of a constructor declaration with no access modifier? (I’m guessing it is the default(package accessible) like other java classes’ constructors.)

I found some reference documents related to this, but couldn’t find the exact answer. Here’s what I’ve found,

1. Java8 JLS 8.9.2, In an enum declaration, a constructor declaration with no access modifiers is private.
2. Java7 JLS 8.9.2, If an enum type has no constructor declarations, then a private constructor that takes no parameters (to match the implicit empty argument list) is automatically provided.

Answer

From when enum constructor’s default access modifier be “private”?

Always. You can’t make new enums, that’s sort of the point of them. You can’t have a non-private constructor of enums (with javac from openjdk16):

> cat Test.java
public enum Test {
  FOO, BAR;
  public Test() {}
}
> javac Test.java
Test.java:3: error: modifier public not allowed here

Let’s try with java6 (Yes, I have javac6 lying around, and can run it on new javas).

> java -jar javac6.jar -bootclasspath openjdk6-rt.jar Test.java
Test.java:3: error: modifier public not allowed here

So, that error hasn’t changed in 2 decades.

Let’s check the access level in javac6!

> cat Test.java
public enum Test {
    FOO, BAR;
    Test() {}
}
> java -jar javac6.jar -bootclasspath openjdk6-rt.jar Test.java
> javap -c -private Test
.... lots of decompiled bytecode

private Test();
    Code:
       0: aload_0
       1: aload_1
       2: iload_2
       3: invokespecial #18                 // Method java/lang/Enum."<init>":(Ljava/lang/String;I)V
       6: return

... more decompiled bytecode

Thus, private. Always been, Always will be. It’s like asking: “Did circles ever have corners?”.

The answer is: No. Never ever. If ever a circle had a corner, it ceases to be one. An enum with a public constructor isn’t an enum.