Java：“试图分配较弱的访问特权错误”（使用1.8编译JDK 1.6 Source）

Question

Using Gradle, we are trying to compile legacy Java code, which was developed for JDK 1.6 with a JDK 1.8 compiler. At some point the compilation process quits with the error

attempting to assign weaker access privileges; was public

(The cause of the error itself is obvious: we have a method in an abstract class, which is declared public , but the implementing class declares it as protected .)

Using JDK 1.6 for compiling, we never had any issues with this. Now for several reasons, we have to compile our code with Java 8, having us run into this issue.

We already tried project setting -PsourceCompatibility=1.6 (also -PtargetCompatibility=1.8 ) when building, without effect.

At the moment, refactoring the whole product code (expecting more and similar errors to follow) is no option, so we are looking for a solution to build the old code with the new JDK.

Any help for this?

Answer 1

The only explanation to the fact that your system used to work with Java 1.6 is that the method access in the superclass has been changed to public without recompiling the subclass. Lowering accessibility in a subclass has been prohibited from the beginning.

Java Language Specification 1.6 provides this explanation on page 344:

if the package points defines the class Point :

 package points; public class Point { public int x, y; protected void print() { System.out.println("(" + x + "," + y + ")"); } } 

used by the Test program:

 class Test extends points.Point { protected void print() { System.out.println("Test"); } public static void main(String[] args) { Test t = new Test(); t.print(); } } 

then these classes compile and Test executes to produce the output:

 Test 

If the method print in class Point is changed to be public , and then only the Point class is recompiled, and then executed with the previously existing binary for Test then no linkage error occurs, even though it is improper, at compile time, for a public method to be overridden by a protected method ( as shown by the fact that the class Test could not be recompiled using this new Point class unless print were changed to be public .) (emphasis added)

If you must re-create the exact behavior with Java 1.8 compiler, change accessibility in the superclass to protected , compile the superclass and subclass, then change accessibility in the superclass back to public , and compile only the superclass. However, at this point I would strongly recommend changing the subclass to provide proper accessibility.