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Other kinds of compatibility include serial compatibility for Serializable types and migration compatibility. Migration compatibility was a constraint on how generics were added to the platform; libraries and their clients had to be able to be generified independently while preserving the ability of code to be compiled and run.

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In the original version of Lib, a call to foo with an integer argument will resolve to foo(double) and under the rules for method invocation conversion the value of the int argument will be converted to a double through a primitive widening conversion. So given client code

public class Client {
  public static void main(String... args) {
    int i = 42;
    double d = (new Lib()).foo(i);
  }
}

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