RFR: 8265418: Clean-up redundant null-checks of Class.getPackageName() [v2]

[Claes Redestad]

On Mon, 26 Apr 2021 11:24:23 GMT, Сергей Цыпанов <github.com+10835776+stsypanov at openjdk.org> wrote:

>> That should be fine, the null check in Objects.equals is benign with these usages.
>
> One more thing I'm thinking about (not to be done in this PR of course) is to move call to `String.intern()` from where it is now in `Class.getPackageName()`
> 
> public String getPackageName() {
>     String pn = this.packageName;
>     if (pn == null) {
>         Class<?> c = this;
>         while (c.isArray()) {
>             c = c.getComponentType();
>         }
>         if (c.isPrimitive()) {
>             pn = "java.lang";
>         } else {
>             String cn = c.getName();
>             int dot = cn.lastIndexOf('.');
>             pn = (dot != -1) ? cn.substring(0, dot).intern() : "";    // <---
>         }
>         this.packageName = pn;
>     }
>     return pn;
> }
> 
> to `packageName` field assignement like
> 
> this.packageName = pn.intern();
> 
> this would add two more Strings (`""` and `"java.lang"`) into string table and allow to avoid `String.equals()` in favour of `==` call when comparing package names. What do you think?

String literals are implicitly interned:

System.out.println("" == new String("")); // false
System.out.println("" == new String("").intern()); // true
System.out.println("java.lang" == new String("java.lang")); // false
System.out.println("java.lang" == new String("java.lang").intern()); // true


So we could already use `==`  instead of `equals` when evaluating the result of `getPackageName`, which might be a good optimization in some places (`ReflectionFactory::isSamePackage` shows up in profiles of some reflection-related benchmarks).

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PR: https://git.openjdk.java.net/jdk/pull/3571