In Vogue Dynamic. Alexander Shopov

Transcription

1 In Vogue Dynamic Alexander Shopov

2 ~]$ whoami By day: Software Engineer at Cisco {,Nov. 28} By night: OSS contributor Coordinator of Bulgarian Gnome TP Git speaks Bulgarian Contacts: Jabber: LinkedIn: SlideShare: GitHub: Web: Just search al_shopov

3 Please Learn and Share License: Creative Commons Attribution 4.0 International CC-BY v4.0

4 Disclaimer My opinions, knowledge and experience! Not my employer's.

5 Menu for Today Numbers Letters Sentences Poetry

6 Numbers

7 Hundred 100

8 Hundred Is a Wonderful Number 100 = ( )²

9 Hundred Is a Wonderful Hectonumber 100 = ( )² = 1³ + 2³ + 3³ + 4³

10 100 Hundred Is a Wonderful Hectonumber = ( )² = 1³ + 2³ + 3³ + 4³ Νικόμαχος was here!

11 100 Hundred Is a Wonderful Hectonumber = ( )² = 1³ + 2³ + 3³ + 4³ Νικόμαχος was here! A Very Bold Comic Sans Relief

12 Triple Hundred Is Even More Magical

13 Triple Hundred by Any Other Base Will Smell as Sweet ₂ 444₈ 292₁₀

14 Our Last Numerological Slide 292

15 The One and Only JSR 292 JSR 292 specified a new bytecode instruction: invokedynamic First and only in all the history of Java platform and technologies. There have been retired instructions jsr, jsr_w cannot appear in class file version 51.0 (JDK 7.0) and above; Together with ret were used for the finally block in Java < 1.5; Mainly used for obfuscation.

16 Letters

17 Bytecode? Who Cares? And It Is Not for Java Well it is also for Java, especially 8.0; And it is also for dynamic languages; And it is also for static languages; And it is also for way too many other things; But yeah, the lecture is about bytecode, so this is last chance to leave (run to the hills)

18 Bytecodes Are the Letters of JVM

19 Bytecode Crash Course in F4 F3 Thread A F2 F1 Thread B F2 F1 Thread C F1 Thread D F3 F2 F1 F0 F0 F0 F0

20 Bytecode Crash Course in JVM (heap) Local variables PC Class code F0 Class Pool of constants Stack

21 Bytecode Crash Course in byte sized, typed instructions; Bytecodes can encode information in themselves, retrieve things from class bytestream, constant pool, local variables array; Perform computations only on stack; Store temporary results in local variables array (non-visible after method call); Store more permanent results in object/class fields (visible after method call); Enter frame by method call; Exit frame by a return from with a possible result (top thing on stack), or by throwing top of stack; JVM can also throw and unroll frames;

22 Bytecode Crash Course in You print the bytecode with the javap command: javap -l -v -p -constants -s -cp CLASSPATH CLASSES

23 For More Info Check my other presentation: Lifting The Veil Reading Java Bytecode During Lunchtime

24 Most Bytecodes Are Very Dull They are lowercase letters they continue or are a part of a single computational sequence: The operate on a single stack; Inside a single frame; They are part of a single method call.

25 Sentences

26 The Uppercase Bytecodes Are the 5 bytecodes that invoke methods (start sentences) in some way. invokestatic (0xb8) invokevirtual (0xb6) invokeinterface (0xb9) invokespecial (0xb7) invokedynamic (0xba)

27 The Punctuations Just for completeness there are only 2 ways to end a sentence (method call): Normal returning by: areturn, dreturn, freturn, ireturn, lreturn, return; Abrupt exception: Either we throw via athrow Or the JVM throws itself

28 Let's Check Simple Sentences package org.kambanaria.standardinvoke; public class Examples { public static int I_STATIC() { int a = Integer.parseInt("7"); return a; } }

29 Decompile Classfile /Java/StandardInvoke/target/classes/org/kambanaria/standardinvoke/Examples.class Last modified ; size 477 bytes MD5 checksum 2b499f0d33b9e2ed f767bb95 Compiled from "Examples.java" public class org.kambanaria.standardinvoke.examples SourceFile: "Examples.java" minor version: 0 major version: 51 flags: ACC_PUBLIC, ACC_SUPER Constant pool: #1 = ref #5.#19 // java/lang/object."<init>":()v #2 = String #20 // 7 #3 = ref #21.#22 // java/lang/integer.parseint:(ljava/lang/string;)i #4 = Class #23 // org/kambanaria/standardinvoke/examples #5 = Class #24 // java/lang/object #6 = Utf8 <init> #7 = Utf8 ()V #8 = Utf8 Code #9 = Utf8 LineNumberTable #10 = Utf8 LocalVariableTable #11 = Utf8 this #12 = Utf8 Lorg/kambanaria/standardinvoke/Examples; #13 = Utf8 I_STATIC #14 = Utf8 ()I #15 = Utf8 a #16 = Utf8 I #17 = Utf8 SourceFile #18 = Utf8 Examples.java #19 = NameAndType #6:#7 // "<init>":()v #20 = Utf8 7 #21 = Class #25 // java/lang/integer #22 = NameAndType #26:#27 // parseint:(ljava/lang/string;)i #23 = Utf8 org/kambanaria/standardinvoke/examples #24 = Utf8 java/lang/object #25 = Utf8 java/lang/integer #26 = Utf8 parseint #27 = Utf8 (Ljava/lang/String;)I { } public org.kambanaria.standardinvoke.examples(); Signature: ()V flags: ACC_PUBLIC LineNumberTable: line 3: 0 LocalVariableTable: Start Length Slot Name Signature this Lorg/kambanaria/standardinvoke/Examples; Code: stack=1, locals=1, args_size=1 0: aload_0 1: invokespecial #1 // java/lang/object."<init>":()v 4: return LineNumberTable: line 3: 0 LocalVariableTable: Start Length Slot Name Signature this Lorg/kambanaria/standardinvoke/Examples; public static int I_STATIC(); Signature: ()I flags: ACC_PUBLIC, ACC_STATIC LineNumberTable: line 6: 0 line 7: 6 LocalVariableTable: Start Length Slot Name Signature a I Code: stack=1, locals=1, args_size=0 0: ldc #2 // String 7 2: invokestatic #3 // java/lang/integer.parseint:(ljava/lang/string;)i 5: istore_0 6: iload_0 7: ireturn LineNumberTable: line 6: 0 line 7: 6 LocalVariableTable: Start Length Slot Name Signature a I

30 But It Is Actually Simple Classfile /Java/StandardInvoke/target/classes/org/kambanaria/standardinvoke/Examples.class Last modified Stats ; size 477 About bytes Class MD5 checksum 2b499f0d33b9e2ed f767bb95 Compiled from "Examples.java" public class org.kambanaria.standardinvoke.examples SourceFile: "Examples.java" minor version: 0 major version: 51 flags: ACC_PUBLIC, ACC_SUPER Constant pool: #1 = ref #5.#19 // java/lang/object."<init>":()v #2 = String #20 // 7 #3 = ref #21.#22 // java/lang/integer.parseint:(ljava/lang/string;)i #4 = Class #23 // org/kambanaria/standardinvoke/examples #5 = Class #24 // java/lang/object #6 = Utf8 <init> #7 = Utf8 ()V #8 = Utf8 Code #9 = Utf8 LineNumberTable #10 = Utf8 LocalVariableTable #11 = Utf8 this #12 = Utf8 Constant Lorg/kambanaria/standardinvoke/Examples; Pool #13 = Utf8 I_STATIC #14 = Utf8 ()I #15 = Utf8 a #16 = Utf8 I #17 = Utf8 SourceFile #18 = Utf8 Examples.java #19 = NameAndType #6:#7 // "<init>":()v #20 = Utf8 7 #21 = Class #25 // java/lang/integer #22 = NameAndType #26:#27 // parseint:(ljava/lang/string;)i #23 = Utf8 org/kambanaria/standardinvoke/examples #24 = Utf8 java/lang/object #25 = Utf8 java/lang/integer #26 = Utf8 parseint #27 = Utf8 (Ljava/lang/String;)I { } public org.kambanaria.standardinvoke.examples(); Signature: ()V flags: ACC_PUBLIC LineNumberTable: line 3: 0 LocalVariableTable: Start Length Slot Name Signature Default this Lorg/kambanaria/standardinvoke/Examples; Constructor Code: stack=1, locals=1, args_size=1 0: aload_0 1: invokespecial #1 // java/lang/object."<init>":()v 4: return LineNumberTable: line 3: 0 LocalVariableTable: Start Length Slot Name Signature this Lorg/kambanaria/standardinvoke/Examples; public static int I_STATIC(); Signature: ()I flags: ACC_PUBLIC, ACC_STATIC LineNumberTable: line 6: 0 line 7: 6 LocalVariableTable: Start Length Slot Name Signature a I Code: I_STATIC method stack=1, locals=1, args_size=0 0: ldc #2 // String 7 2: invokestatic #3 // java/lang/integer.parseint:(ljava/lang/string;)i 5: istore_0 6: iload_0 7: ireturn LineNumberTable: line 6: 0 line 7: 6 LocalVariableTable: Start Length Slot Name Signature a I

31 But It Is Actually Very Simple Classfile /Java/StandardInvoke/target/classes/org/kambanaria/standardinvoke/Examples.class Last modified Stats ; size 477 About bytes Class MD5 checksum 2b499f0d33b9e2ed f767bb95 Compiled from "Examples.java" public class org.kambanaria.standardinvoke.examples SourceFile: "Examples.java" minor version: 0 major version: 51 flags: ACC_PUBLIC, ACC_SUPER Constant pool: #1 = ref #5.#19 // java/lang/object."<init>":()v #2 = String #20 // 7 #3 = ref #21.#22 // java/lang/integer.parseint:(ljava/lang/string;)i #4 = Class #23 // org/kambanaria/standardinvoke/examples #5 = Class #24 // java/lang/object #6 = Utf8 <init> #7 = Utf8 ()V #8 = Utf8 Code #9 = Utf8 LineNumberTable #10 = Utf8 LocalVariableTable #11 = Utf8 this #12 = Utf8 Constant Lorg/kambanaria/standardinvoke/Examples; Pool #13 = Utf8 I_STATIC #14 = Utf8 ()I #15 = Utf8 a #16 = Utf8 I #17 = Utf8 SourceFile #18 = Utf8 Examples.java #19 = NameAndType #6:#7 // "<init>":()v #20 = Utf8 7 #21 = Class #25 // java/lang/integer #22 = NameAndType #26:#27 // parseint:(ljava/lang/string;)i #23 = Utf8 org/kambanaria/standardinvoke/examples #24 = Utf8 java/lang/object #25 = Utf8 java/lang/integer #26 = Utf8 parseint #27 = Utf8 (Ljava/lang/String;)I { } public org.kambanaria.standardinvoke.examples(); Signature: ()V flags: ACC_PUBLIC LineNumberTable: line 3: 0 LocalVariableTable: Start Length Slot Name Signature Default this Lorg/kambanaria/standardinvoke/Examples; Constructor Code: stack=1, locals=1, args_size=1 0: aload_0 1: invokespecial #1 // java/lang/object."<init>":()v 4: return LineNumberTable: line 3: 0 LocalVariableTable: Start Length Slot Name Signature this Lorg/kambanaria/standardinvoke/Examples; public static int I_STATIC(); Signature: ()I flags: ACC_PUBLIC, I_STATIC ACC_STATIC stats 1 LineNumberTable: line 6: 0 line 7: 6 LocalVariableTable: Start Length Slot Name Signature a I Code: stack=1, locals=1, I_STATIC args_size=0 code 0: ldc #2 // String 7 2: invokestatic #3 // java/lang/integer.parseint:(ljava/lang/string;)i 5: istore_0 6: iload_0 7: ireturn LineNumberTable: line 6: I_STATIC 0 stats 2 line 7: 6 LocalVariableTable: Start Length Slot Name Signature a I

32 The Whole Assembler Code: stack=1, locals=1, args_size=0 0: ldc #2 2: invokestatic #3 5: istore_0 6: iload_0 7: ireturn

33 Physical Layout Code: stack=1, locals=1, args_size=0 0: ldc #2 2: invokestatic #3 5: istore_0 6: iload_0 7: ireturn od -x --endian=big./examples.class b b 1a ac

34 ldc Is 0x12, 1 Byte Reference to Constant Pool Code: stack=1, locals=1, args_size=0 0: ldc #2 2: invokestatic #3 5: istore_0 6: iload_0 7: ireturn od -x --endian=big./examples.class b b 1a #2 in Constant Pool: String 7 ac

35 invokestatic Is 0xb8, 2 Bytes Reference (00<<8+03==03) Code: stack=1, locals=1, args_size=0 0: ldc #2 2: invokestatic #3 5: istore_0 #3 in Constant Pool points: 6: iload_0 7: ireturn java/lang/integer.parseint: (Ljava/lang/String;)I od -x --endian=big./examples.class b b 1a ac

36 istore_0 Is 0x3b, iload_0 Is 0x1a, ireturn Is 0xac Code: stack=1, locals=1, args_size=0 0: ldc #2 2: invokestatic #3 5: istore_0 6: iload_0 7: ireturn od -x --endian=big./examples.class b b 1a ac

37 Let's Check Another Sentence public static void I_VIRTUAL() throws InterruptedException { "7".wait(3, 7); }

38 As Before Push Arguments Onto Stack, Invoke Name + Signature public static void I_VIRTUAL() Code: 0: ldc #2 // String 7 2: ldc2_w #4 // long 3l 5: bipush 7 7: invokevirtual #6 // java/lang/object.wait:(ji)v 10: return

39 Let's Check the Rest of Old Invoke Instructions public static int I_INTERFACE(){ return "7".compareTo("8"); } public static Object I_SPECIAL(){ return new Integer(5); } // also private methods, super

40 As Before Push Arguments Onto Stack, Invoke Name + Signature I_INTERFACE(); Code: 0: ldc #2 // "7" 2: ldc #7 // "8" 4: invokevirtual #8 // // String.compareTo 7: ireturn I_SPECIAL(); Code: 0: new #9 //class j/l/integer 3: dup 4: iconst_5 5: invokespecial #10 // Integer. //"<init>":(i)v 8: areturn

41 Fundamentally Traditional Invokes: Are scoped Java-ish (class or interface); Have a Java-ish receiver (single or none); And definitely do Java-ish dispatch; Everything else you have to simulate.

42 Now Here Comes Java 8, Functional Interfaces, Lambdas public static void notempty(collection<string> all) { all.removeif(string::isempty); }

43 Which is Syntactic Sugar for an Anonymous Inner Class public static void notemptyold(collection<string> all) { all.removeif(new Predicate<String>() public boolean test(string t) { return t.isempty(); } }); }

44 Which is Syntactic Sugar For An New Object Anonymous Inner Class Per Invocation public static void notemptyold(collection<string> all) { all.removeif(new Predicate<String>() public boolean test(string t) { return t.isempty(); } }); }

45 Which is Syntactic Sugar For An New Object Anonymous Inner Class Per Invocation public static void notemptyold(collection<string> all) { all.removeif(new Predicate<String>() public boolean test(string t) { return t.isempty(); } }); } A Whole New Class

46 Improve by Caching public static void nonemptyoldneat(collection<string> all) { all.removeif(nonemptyp); } private static Predicate<String> nonemptyp = new Predicate<String>() public boolean test(string t) { return t.isempty(); } };

47 Improve by Caching public static void nonemptyoldneat(collection<string> all) { all.removeif(nonemptyp); } private static Predicate<String> nonemptyp = new Predicate<String>() public boolean }; test(string t) { return t.isempty(); } A Whole New Class

48 Let's Disassemble nonempty nonempty Code: 0: aload_0 //Load ref to col on stack 1: invokedynamic #2, 0 // Here's Waldo // Magic! 6: invokeinterface #3, 2 // Collection.removeIf 11: pop // pop boolean from stack 12: return // we are ready }

49 Let's Disassemble nonempty 1: invokedynamic #2, 0 // That is ba when dumped // #2 in constant pool is: InvokeDynamic #0:test:()Ljava/util/function/Predicate; // void -> Predicate, has index 0, OK // Where is String.isEmpty?

50 At the End of the Class Bootstraps: 0: #25 invokestatic j/l/invoke/lambdametafactory.metafactory:( Ljava/lang/invoke/Handles$Lookup; Ljava/lang/String; Ljava/lang/invoke/Type; Ljava/lang/invoke/Type; Ljava/lang/invoke/Handle; Ljava/lang/invoke/Type;) Ljava/lang/invoke/CallSite; arguments: #26 (Ljava/lang/Object;)Z #27 invokevirtual j/l/string.isempty:()z #28 (Ljava/lang/String;)Z

51 At the End of the Class Index 0 Bootstraps: 0: #25 invokestatic j/l/invoke/lambdametafactory.metafactory:( Ljava/lang/invoke/Handles$Lookup; Ljava/lang/String; Ljava/lang/invoke/Type; Ljava/lang/invoke/Type; Ljava/lang/invoke/Handle; Ljava/lang/invoke/Type;) Ljava/lang/invoke/CallSite; arguments: #26 (Ljava/lang/Object;)Z #27 invokevirtual j/l/string.isempty:()z #28 (Ljava/lang/String;)Z

52 At the End of the Class Fat Factory Gives CallSite, not Predicate Bootstraps: 0: #25 invokestatic j/l/invoke/lambdametafactory.metafactory:( Ljava/lang/invoke/Handles$Lookup; Ljava/lang/String; Ljava/lang/invoke/Type; Ljava/lang/invoke/Type; Ljava/lang/invoke/Handle; Ljava/lang/invoke/Type;) Ljava/lang/invoke/CallSite; arguments: #26 (Ljava/lang/Object;)Z #27 invokevirtual j/l/string.isempty:()z #28 (Ljava/lang/String;)Z

53 At the End of the Class Bootstraps: 0: #25 invokestatic j/l/invoke/lambdametafactory.metafactory:( Ljava/lang/invoke/Handles$Lookup; Ljava/lang/String; Ljava/lang/invoke/Type; Ljava/lang/invoke/Type; Ljava/lang/invoke/Handle; Ljava/lang/invoke/Type;) Ljava/lang/invoke/CallSite; Here Is the Test arguments: #26 (Ljava/lang/Object;)Z #27 invokevirtual j/l/string.isempty:()z #28 (Ljava/lang/String;)Z

54 Let's Try a More Realistic nonempty public static void nonempty(collection<string> all) { all.removeif(s -> s == null s.trim().isempty()); }

55 The nonempty Stays the Same nonempty Code: 0: aload_0 //Load ref to col on stack 1: invokedynamic #2, 0 // Here's Waldo // Magic! 6: invokeinterface #3, 2 // Collection.removeIf 11: pop // pop boolean from stack 12: return // we are ready }

56 We Get a Private, Static, Synthetic lambda$nonempty$0 lambda$nonempty$0 // (Ljava/lang/String;)Z Code: 0: aload_0 1: ifnull 14 4: aload_0 5: invokevirtual #4 // String.trim 8: invokevirtual #5 // String.isEmpty 11: ifeq 18 14: iconst_1 15: goto 19 18: iconst_0 19: ireturn

57 Which in Java Terms is private static void lambda$nonempty$0(string s) { return s == null s.trim().isempty(); }

58 The Bootstap Glue Becomes Bootstraps: 0: #23 invokestatic j/l/invoke/lambdametafactory.metafactory:( Ljava/lang/invoke/Handles$Lookup; Ljava/lang/String; Ljava/lang/invoke/Type; Ljava/lang/invoke/Type; Ljava/lang/invoke/Handle; Ljava/lang/invoke/Type;) Ljava/lang/invoke/CallSite; arguments: #24 (Ljava/lang/Object;)Z #25 invokestatic org/kambanaria/invokedynamic/ Examples.lambda$nonEmpty$0:(Ljava/lang/String;)Z #26 (Ljava/lang/String;)Z

59 Seems We Are Winning Lambdas get to be called with invokedynamic Which refers some glue code (bootstrap method) Which refers either: Some existing method (String::isEmpty); A new custom method (lambda$nonempty$0). No need to reuse a static instance; No new inner class!

60 Another Win for the Fundamental Theorem of Software Engineering David Wheeler But what is that theorem?

61 The Traditional Invoke Instructions Have a precise Java-ish meaning; They point to some executable code by: Name; Signature. Somewhat eased by boxing/varargs. What they actually point to is a string in the constant pool that gives name + signature. Given that JVM does a predefined resolution.

62 Old Invokes invoke type Name + signature JVM Decision by JVM JVM code code code

63 Invokedynamic We Get to Decide (This Is not the Whole Picture) invoke dynamic Decision by Us Bootstrap CallSite JVM Decision by Us Handle Decision by Us JVM code code code

64 The Fundamental Theorem of Software Engineering All problems in computer science can be solved by another level of indirection, except of course for the problem of too many indirections. David Wheeler

65 Poetry

66 Prose Poetry Using invokedynamic we can tell the JVM that a particular phrase (callsite) points to a particular code has a particular meaning; This can be very dull, repetitive and prosaic; In poetry you can talk about one thing but mean another; And even when things are ambiguous or just not the right types, number or order it works fine; And it is always in vogue; And as rapping has shown it can be fast!

67 How Does Invokedynamic Exactly Work A dynamic call site is every lexical occurrence of invokedynamic; Thus EVERY occurrence can behave differently; The instruction is followed by 4 bytes, only the fist 2 of them are currently used, the rest must be 0; The 1 st 2 bytes point to an index in the constant that contains a call site specifier that leads to a j.l.invoke.handle that serves as a bootstrap method; The bootstrap method is invoked and returns a j.l.invoke.callsite, this is bound permanently to this call site; The CallSite object provides a Handle via gettarget() method which provides the exact behavior. The result of gettarget() CAN change!

68 Invokedynamic JVM JVM code invoke dynamic code code

69 Invokedynamic JVM JVM code invoke dynamic Handle Bootstrap code code

70 Invokedynamic JVM JVM code invoke dynamic Handle Bootstrap code CallSite code

71 Invokedynamic JVM JVM code invoke dynamic Handle Bootstrap code CallSite code

72 Invokedynamic JVM JVM code invoke dynamic CallSite code code

73 Invokedynamic JVM Handle JVM code invoke dynamic CallSite Handle code Handle code

74 Invokedynamic JVM Handle JVM code invoke dynamic CallSite Handle code Handle code

75 Invokedynamic JVM Handle JVM code invoke dynamic CallSite Handle code Handle code

76 Handles vs. Reflection Reflections allows you to look at yourself and discover things, they are closer to Java language constructs; Hadles assume you know what you are looking for no exploration, but they are closer to the way JVM functions they are fast. Using them is like shaving in the dark you have to know where the razor is, how much foam to squeeze, what you are shaving but you can do it fast since your hands know their way they have memory of their own.

77 But Wait Types Must Match! You cannot pass some number of arguments to a method that expects another number Except varargs You cannot pass different types of arguments Except boxing/unboxing You cannot reorder; You cannot group; You cannot aggregate.

78 You Cannot Put a Square Peg In a Round Whole

79 But You Actually Can

80 Reshape the Peg to Be No Longer Square But Round and It Fits

81 Handles Know Types JVM JVM code invoke dynamic CallSite Handle code Handle code

82 But You Can Convert/Reshape/ Rechisel the JVM Way JVM Handle JVM code invoke dynamic CallSite Handle code Handle Handle code

83 java.lang.invoke In a Nutshell CallSite (Constant/Mutable/Volatile) produces Handle Type represents types Handle reference to method, (static) field, array member access; Handles combining or producing handles; Handles.Lookup get a Handle referring to actual method, filed, array member; HandleProxies proxies interface-handle; SwitchPoint fast, one-way if-then-else for handles;

84 Example Curry public class Computer { public static int sum (int a, int b){ return a + b; } }

85 Example Curry Computer.sum(2, 7); // => 9 // What we can see Handles.Lookup lookup = Handles.lookup(); Type sumtype = Type.methodType( // result, 1 arg,, 2 arg int.class, int.class, int.class); Handle sumhandle = lookup.findstatic( Computer.class, "sum", sumtype); sumhandle.invoke(2, 7); // => 9 Handle add2handle = Handles. insertarguments(sumhandle, 0, 2); add2handle.invokewitharguments(7); // => 9

86 Example Switch Receiver and Arg "tom".concat("cat"); // => "tomcat" "cat".concat("tom"); // => "cattom"

87 Example Switch Receiver and Argument Type cattype = Type.methodType( // result, argument String.class, String.class); Handle cathandle = lookup.findvirtual( String.class, "concat",cattype); cathandle.invoke("tom", "cat"); // "tomcat" Type tactype = Type.methodType( // result, receiver, argument String.class, String.class, String.class); Handle tachandle = Handles. permutearguments(cathandle, tactype, 1, 0); tachandle.invoke("tom", "cat"); // "cattom"

88 Rhymes And Allusions Rhymes get from repetition of sounds and you get to make Handles from other Hadles all the way turtles go; You can adapt and convert types thus you can use a MethotHandle with one type for something else with a different type. You can write one stanza but use it for many contexts; JVM actually understands this algebra of handles and types and can optimize it.

89 If You Are Not So Much Into Poetry

90 Shameless Plug for Geertjan & NetBeans

91 Shameless Plug for Geertjan & NetBeans

92 Shameless Plug for Geertjan & NetBeans

93 Shameless Plug for Geertjan & NetBeans

94 Further Resources Nutter, Ch. (headius JRuby guy) Invokedynamic: Changing the JVM Forever Invokedynamic in 45 minutes Indy Deep Dive Worthington, J.: Using invokedynamic to teach the JVM a new language Rose, J.: Bytecodes meet combinators: invokedynamic on the JVM Ponge, J: Demystifying invokedynamic, Java Magazine 2013, January-February: Part 1, May-June: Part 2 Forax, R.: jsr292-cookbook

95 Images rosipaw: 146/365 square peg into a round hole CC BY-NC-SA 2.0 Eric: Lego Porn CC BY-NC-SA 2.0