Higher-Order Problems (“Objects are Multi-Entry Closures”)

Package Server:

public class A {

…

public void method1(A a) {

… }

}

public class B extends A {

…

public void method1(A a) {

B b = (B)a;

… }

}

Package Client2;

class C {

...

void method4(D d) {

…

d.method3();

…

}

Package Client1;

public class D {

A anA = A( … ) ;

B a_B = B( … ) ;

public void method3() {

... a_b.method1

(… (B)anA … )

...

anA = a_B; }

}

Object d is passed in, call to method3 triggers exception

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