Consider the following code:

class Test {
    class Inner {}

    void test() {
        new Test.Inner(); // compiles successfully
        this.new Test.Inner(); // error
    }
}

javac reports:
Test.java:6: error: '(' expected
        this.new Test.Inner();
                     ^
1 error

However, per JLS 15.9, such code should be accepted. (Relative to JLS7, JLS8 expanded the grammar of class instance creation expressions. See http://mail.openjdk.java.net/pipermail/compiler-dev/2019-January/012923.html for details.)