Héritage et polymorphisme

Main.java

public class Main {
	private static class A {
		protected void foo() {
			System.out.println("A");
		}
	}

	private static class B extends A {
		@Override
		protected void foo() {
			System.out.println("B");
		}
	}

	public static void main(final String[] args) {
		final A a = new A();
		a.foo();

		final B b = new B();
		b.foo();

		final A c = b;
		c.foo();
	}
}

Main1.cs

using System;

namespace Foo {
    public class Bar {
        private class A {
            public void Foo() {
                Console.Out.WriteLine("A");
            }
        }

        private class B : A {
            public void Foo() {
                Console.Out.WriteLine("B");
            }
        }

        public static void Main(string[] args) {
            A a = new A();
            a.Foo();

            B b = new B();
            b.Foo();

            A c = b;
            c.Foo();
        }
    }
}

Main2.cs

using System;

namespace Foo {
    public class Bar {
        private class A {
            public void Foo() {
                Console.Out.WriteLine("A");
            }
        }

        private class B : A {
            public new void Foo() {
                Console.Out.WriteLine("B");
            }
        }

        public static void Main(string[] args) {
            A a = new A();
            a.Foo();

            B b = new B();
            b.Foo();

            A c = b;
            c.Foo();
        }
    }
}

Main3.cs

using System;

namespace Foo {
    public class Bar {
        private class A {
            public virtual void Foo() {
                Console.Out.WriteLine("A");
            }
        }

        private class B : A {
            public override void Foo() {
                Console.Out.WriteLine("B");
            }
        }

        public static void Main(string[] args) {
            A a = new A();
            a.Foo();

            B b = new B();
            b.Foo();

            A c = b;
            c.Foo();
        }
    }
}

Main4.cs

using System;

namespace Foo
{
    public class Bar {
        private class A {
            public void Foo() {
                Console.Out.WriteLine("A");
            }
        }

        private class B : A {
            public override void Foo() {
                Console.Out.WriteLine("B");
            }
        }

        public static void Main(string[] args) {
            A a = new A();
            a.Foo();

            B b = new B();
            b.Foo();

            A c = b;
            c.Foo();
        }
    }
}