Default method in interface? #13
Comments
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I noticed earlier today when trying to switch from Java 8 to Java 7 in Eclipse that it got in a weird state, where it started moaning about default methods in anonymous So I created an empty project with just one test containing a lambda and 'retrolambda' was able to convert it to Java 7, but the moment I tried to implement This is very limiting, and in our case means we would have to write our own bubble sort implementation, so we could avoid the |
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I found the cause (JDK 8 generates bridge methods to interfaces when overriding a method to refine its return type) and released Retrolambda 1.1.4 which includes a fix for it. Please try it to see if it helps (and whether there are still other issues). I couldn't figure out how to make Gradle use the new Retrolambda version, so I could not test it on your project, but that's probably just because I don't know Gradle. |
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Excellent work! I too was also unable to get the Gradle plug-in to use the latest version of retrolambda, so have raised an issue (evant/gradle-retrolambda#20) to help improve the documentation in this area. Will let you know how this fix works out for me once I'm able to test it. |
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It sounds like you've already seen this for yourself, but our complete build is now passing. Thanks so much for the rapid turn around on this. |
public interface MyInterface {
default String def() {
return "[" + toString() + ", " + "def]";
}
default String join(MyInterface other) {
return def() + other.def();
}
}
class C implements MyInterface{} compiles to:
public class testpackage.MyClass implements testpackage.MyInterface {
public testpackage.MyClass();
Code:
0: aload_0
1: invokespecial luontola#16 // Method java/lang/Object."<init>":()V
4: return
public java.lang.String join(testpackage.MyInterface);
Code:
0: aload_0
1: aload_1
2: invokestatic luontola#46 // Method testpackage/MyInterfacehelper.join:(Ltestpackage/MyInterface;Ltestpackage/MyInterface;)Ljava/lang/String;
5: areturn
public java.lang.String def();
Code:
0: aload_0
1: invokestatic luontola#49 // Method testpackage/MyInterfacehelper.def:(Ltestpackage/MyInterface;)Ljava/lang/String;
4: areturn
}
Where testpackage.MyInterfacehelper is compiled to
public class testpackage.MyInterfacehelper {
private testpackage.MyInterfacehelper();
Code:
0: aload_0
1: invokespecial luontola#9 // Method java/lang/Object."<init>":()V
4: return
public static java.lang.String def(testpackage.MyInterface);
Code:
0: new luontola#13 // class java/lang/StringBuilder
3: dup
4: invokespecial luontola#14 // Method java/lang/StringBuilder."<init>":()V
7: ldc luontola#16 // String [
9: invokevirtual luontola#20 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
12: aload_0
13: invokevirtual luontola#24 // Method java/lang/Object.toString:()Ljava/lang/String;
16: invokevirtual luontola#20 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
19: ldc luontola#26 // String ,
21: invokevirtual luontola#20 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
24: ldc luontola#28 // String def]
26: invokevirtual luontola#20 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
29: invokevirtual luontola#29 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
32: areturn
public static java.lang.String join(testpackage.MyInterface, testpackage.MyInterface);
Code:
0: new luontola#13 // class java/lang/StringBuilder
3: dup
4: invokespecial luontola#14 // Method java/lang/StringBuilder."<init>":()V
7: aload_0
8: invokeinterface luontola#35, 1 // InterfaceMethod testpackage/MyInterface.def:()Ljava/lang/String;
13: invokevirtual luontola#20 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
16: aload_1
17: invokeinterface luontola#35, 1 // InterfaceMethod testpackage/MyInterface.def:()Ljava/lang/String;
22: invokevirtual luontola#20 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
25: invokevirtual luontola#29 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
28: areturn
}
==============
interface StaticTest {
static <T> T staticMethod(T t) {
return t;
}
}
compiles to
public class testpackage.StaticTesthelper {
private testpackage.StaticTesthelper();
Code:
0: aload_0
1: invokespecial luontola#9 // Method java/lang/Object."<init>":()V
4: return
public static <T> T staticMethod$static(T);
Code:
0: aload_0
1: areturn
}
========
Brigde methods are generated properly in example:
public interface BridgeParent<T> {
T get();
}
public interface StringBridges extends BridgeParent<String> {
@OverRide
default String get() {
return "default method";
}
default String concrete() {
return "concrete";
}
}
public class testpackage.StringBridgeshelper
SourceFile: "testpackage/StringBridges.java"
minor version: 0
major version: 50
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
luontola#1 = Utf8 testpackage/StringBridgeshelper
luontola#2 = Class luontola#1 // testpackage/StringBridgeshelper
luontola#3 = Utf8 java/lang/Object
luontola#4 = Class luontola#3 // java/lang/Object
luontola#5 = Utf8 testpackage/StringBridges.java
luontola#6 = Utf8 <init>
luontola#7 = Utf8 ()V
luontola#8 = NameAndType luontola#6:luontola#7 // "<init>":()V
luontola#9 = Methodref luontola#4.luontola#8 // java/lang/Object."<init>":()V
luontola#10 = Utf8 get
luontola#11 = Utf8 (Ltestpackage/StringBridges;)Ljava/lang/String;
luontola#12 = Utf8 default method
luontola#13 = String luontola#12 // default method
luontola#14 = Utf8 concrete
luontola#15 = String luontola#14 // concrete
luontola#16 = Utf8 (Ltestpackage/StringBridges;)Ljava/lang/Object;
luontola#17 = Utf8 testpackage/StringBridges
luontola#18 = Class luontola#17 // testpackage/StringBridges
luontola#19 = Utf8 ()Ljava/lang/String;
luontola#20 = NameAndType luontola#10:luontola#19 // get:()Ljava/lang/String;
luontola#21 = InterfaceMethodref luontola#18.luontola#20 // testpackage/StringBridges.get:()Ljava/lang/String;
luontola#22 = Utf8 Code
luontola#23 = Utf8 LineNumberTable
luontola#24 = Utf8 SourceFile
{
private testpackage.StringBridgeshelper();
descriptor: ()V
flags: ACC_PRIVATE
Code:
stack=1, locals=1, args_size=1
0: aload_0
1: invokespecial luontola#9 // Method java/lang/Object."<init>":()V
4: return
public static java.lang.String get(testpackage.StringBridges);
descriptor: (Ltestpackage/StringBridges;)Ljava/lang/String;
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=1, args_size=1
0: ldc luontola#13 // String default method
2: areturn
LineNumberTable:
line 9: 0
public static java.lang.String concrete(testpackage.StringBridges);
descriptor: (Ltestpackage/StringBridges;)Ljava/lang/String;
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=1, args_size=1
0: ldc luontola#15 // String concrete
2: areturn
LineNumberTable:
line 13: 0
public static java.lang.Object get(testpackage.StringBridges);
descriptor: (Ltestpackage/StringBridges;)Ljava/lang/Object;
flags: ACC_PUBLIC, ACC_STATIC, ACC_BRIDGE, ACC_SYNTHETIC
Code:
stack=1, locals=1, args_size=1
0: aload_0
1: invokeinterface luontola#21, 1 // InterfaceMethod testpackage/StringBridges.get:()Ljava/lang/String;
6: areturn
LineNumberTable:
line 6: 0
}
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i have an error please help me |
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@zzubiplain, this doesn't sound like a retrolambda issue. It sounds like you are trying to compile code containing lambdas with JDK 7, whereas you need to compile with JDK 8. Once compiled however, you can then use retrolambda to convert the bytecode so that it can be run on JRE 7, provided that you didn't make use of any other Java 8 features apart from lambdas. |
Our build fails now that I've started making use of retrolambda (via the gradle plug-in), for a project that was a pure Java 7 code base, with one class (
NodeCommander) converted to make use of Lambdas. The bit that sticks out to me as looking strange is this:Since I'm not making any use of default methods in this, or any other interface. You can see the code for yourself here:
This problem happens both when I configure the
JAVA_7andJAVA_8environment variables on my machine, and when I don't and it uses some built-in compiler. Here's the tail of the build failure log:Any help or pointers for further investigation would be much appreciated.
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