Movatterモバイル変換

Consider the following code:

    public void test(Stream<String> in) {        Set<String> s = SetFactory.newSet();        Stream<Boolean> numbers = in.map(s::contains);    }

Compiled with java 8 B103

public void test(java.util.stream.Stream);    Code:       0: invokestatic  #2                  // Method org/benf/cfr/tests/support/SetFactory.newSet:()Ljava/util/Set;       3: astore_2             4: aload_1              5: aload_2              6: invokedynamic #3,  0              // InvokeDynamic #0:apply:(Ljava/util/Set;)Ljava/util/function/Function;      11: invokeinterface #4,  2            // InterfaceMethod java/util/stream/Stream.map:(Ljava/util/function/Function;)Ljava/util/stream/Stream;      16: astore_3            17: return

Compiled with java 8 B132

public void test(java.util.stream.Stream);    Code:       0: invokestatic  #2                  // Method org/benf/cfr/tests/support/SetFactory.newSet:()Ljava/util/Set;       3: astore_2             4: aload_1              5: aload_2              6: dup                  7: invokevirtual #3                  // Method java/lang/Object.getClass:()Ljava/lang/Class;      10: pop                 11: invokedynamic #4,  0              // InvokeDynamic #0:apply:(Ljava/util/Set;)Ljava/util/function/Function;      16: invokeinterface #5,  2            // InterfaceMethod java/util/stream/Stream.map:(Ljava/util/function/Function;)Ljava/util/stream/Stream;      21: astore_3            22: return

... interesting - B132 adds an explicit call to getClass on the Set s.

I haven't yet found any 'official' description of a reason for this - it seems (internet based wisdom) that it's a null check, though Iimagine that it's there to force any issues with classLoading for s to occur in the explicit original method, as opposed to inside the invokedynamic's builder, thus causing users to get slightly more understandable stack traces in the case of problems.

CFR 0_75 will generate the following.

    public void test(Stream<String> in) {        Set s;        Set set = s = SetFactory.newSet();        set.getClass();        Stream<Boolean> numbers = in.map(set::contains);    }

.... but this is fixed in 0_76

    public void test(Stream<String> in) {        Set s = SetFactory.newSet();        Stream<Boolean> numbers = in.map(s::contains);    }