13.5.2

Superinterfaces

BINARY COMPATIBILITY

13.5.2   Superinterfaces

Changes to the interface hierarchy cause errors in the same way that changes to

the class hierarchy do, as described in  13.4.4. In particular, changes that result in

any previous superinterface of a class no longer being a superinterface can break

compatibility with pre existing binaries, resulting in a

VerifyError

.

13.5.3   The Interface Members

Adding a member to an interface does not break compatibility with pre existing

binaries.

Deleting a member from an interface may cause linkage errors in pre existing

binaries. If the example program:

interface I { void hello(); }

class Test implements I {

public static void main(String[] args) {

I anI = new Test();

anI.hello();

}

public void hello() { System.out.println("hello"); }

}

is compiled and executed, it produces the output:

hello

Suppose that a new version of interface

I

 is compiled:

interface I { }

If

I

 is recompiled but not

Test

, then running the new binary with the existing

binary for

Test

 will result in a

NoSuchMethodError

. (In some early implementa 

tions of Java this program still executed; the fact that the method

hello

 no longer

exists in interface

I

 was not correctly detected.)

13.5.4   Field Declarations

The considerations for changing field declarations in interfaces are the same as

those for

static final

 fields in classes, as described in  13.4.7 and  13.4.8.

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