imagine:
class A {
void foo(){
...
this.bar();
...
}
void bar(){
...
}
}
class B extends A {
//override bar
void bar(){
...
}
}
class C {
void bazz(){
B b = new B();
// which bar would be called?
B.foo();
}
}
As you see in bazz method which bar will be called? the second one the bar in class B will be called. but, what is the problem here? the problem is foo method in class A will not know anything about the override of bar method in class B, Then your invariants may be violated. because foo may expect the only behavior of bar method that is in own class, not something is overridden. This problem is called fragile base-class problem.
