BAEL-4220 | A Guide to IllegalAccessError and when it happens (#10798)

* BAEL-4220 | A Guide to IllegalAccessError and when it happens

* BAEL-4220 | A Guide to IllegalAccessError and when it happens | fix tests

* BAEL-4220 | A Guide to IllegalAccessError and when it happens | fix tests

* BAEL-4220 | A Guide to IllegalAccessError and when it happens | BDD test names

core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/illegalaccesserror/Class1.java

@@ -0,0 +1,8 @@
+package com.baeldung.exceptions.illegalaccesserror;
+
+public class Class1 {
+
+    public void bar() {
+        System.out.println("SUCCESS");
+    }
+}

core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/illegalaccesserror/Class2.java

@@ -0,0 +1,10 @@
+package com.baeldung.exceptions.illegalaccesserror;
+
+public class Class2 {
+
+    public void foo() {
+        Class1 c1 = new Class1();
+        c1.bar();
+    }
+}
+    

core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/illegalaccesserror/IllegalAccessErrorExample.java

@@ -0,0 +1,20 @@
+package com.baeldung.exceptions.illegalaccesserror;
+
+public class IllegalAccessErrorExample {
+
+    interface Baeldung {
+        public default void foobar() {
+            System.out.println("This is a default method.");
+        }
+    }
+
+    class Super {
+        private void foobar() {
+            System.out.println("SuperClass method foobar");
+        }
+    }
+
+    class MySubClass extends Super implements Baeldung {
+
+    }
+}

core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/illegalaccesserror/IllegalAccessErrorSolved.java

@@ -0,0 +1,20 @@
+package com.baeldung.exceptions.illegalaccesserror;
+
+public class IllegalAccessErrorSolved {
+
+    interface BaeldungSolved {
+        public default void foobar() {
+            System.out.println("This is a default method.");
+        }
+    }
+
+    class SuperSolved {
+        public void foobar() {
+            System.out.println("SuperClass method foobar");
+        }
+    }
+
+    class MySubClassSolved extends SuperSolved implements BaeldungSolved {
+
+    }
+}

core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/illegalaccesserror/IllegalAccessErrorExampleUnitTest.java

@@ -0,0 +1,21 @@
+package com.baeldung.exceptions.illegalaccesserror;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class IllegalAccessErrorExampleUnitTest {
+
+    @Test()
+    public void givenInterfaceDefaultMethOverriddenPrivateAccess_whenInvoked_thenIllegalAccessError() {
+        Assertions.assertThrows(IllegalAccessError.class, () -> {
+            new IllegalAccessErrorExample().new MySubClass().foobar();
+        });
+    }
+
+    @Test()
+    public void givenClass1Class2_whenSameClassDefintion_thenNoIllegalAccessError() {
+        Assertions.assertDoesNotThrow(() -> {
+            new Class2().foo();
+        });
+    }
+}

core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/illegalaccesserror/IllegalAccessErrorSolvedUnitTest.java

@@ -0,0 +1,14 @@
+package com.baeldung.exceptions.illegalaccesserror;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class IllegalAccessErrorSolvedUnitTest {
+
+    @Test()
+    public void givenInterfaceDefaultMethOverriddenNonPrivateAccess_whenInvoked_thenNoIllegalAccessError() {
+        Assertions.assertDoesNotThrow(() -> {
+            new IllegalAccessErrorSolved().new MySubClassSolved().foobar();
+        });
+    }
+}