jdk-24/test/langtools/tools/javac/defaultMethods/Neg04.java

/* @test /nodynamiccopyright/
 * @bug 7192246
 * @summary check that default method must have most specific return type
 * @compile/fail/ref=Neg04.out -XDrawDiagnostics Neg04.java
 */

class Neg04 {
    interface IA1 { Integer m(); }
    interface IA2 extends IA1 { default Number m() { return Neg04.m(this); } } //error

    abstract class C implements IA1, IA2 {}

    static int m(IA2 a) { return 0; }
}