funciones - java 8 lambdas pdf
¿Cómo se compilarán las funciones Java lambda? (1)
La VM decide cómo implementar lambda, no un compilador.
Consulte la sección Translation strategy de traducción en Traducción de expresiones lambda .
En lugar de generar bytecode para crear el objeto que implementa la expresión lambda (como llamar a un constructor para una clase interna), describimos una receta para construir el lambda y delegamos la construcción real en el tiempo de ejecución del lenguaje. Esa receta está codificada en las listas de argumentos estáticos y dinámicos de una instrucción invocada dinámica.
for construcción de su ejemplo es la forma más efectiva en términos de simple compilación o rendimiento (pero las diferencias de rendimiento son muy pequeñas, según las pruebas).
Complemento :
Creé y desarmé dos ejemplos:
for (String string: Arrays.asList("hello")) {
System.out.println(string);
}
Código de bytes desensamblado, constantes y otra información:
Classfile LambdaCode.class
Last modified 30.05.2013; size 771 bytes
MD5 checksum 79bf2821b5a14485934e5cebb60c99d6
Compiled from "LambdaCode.java"
public class test.lambda.LambdaCode
SourceFile: "LambdaCode.java"
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #11.#22 // java/lang/Object."<init>":()V
#2 = Class #23 // java/lang/String
#3 = String #24 // hello
#4 = Methodref #25.#26 // java/util/Arrays.asList:([Ljava/lang/Object;)Ljava/util/List;
#5 = InterfaceMethodref #27.#28 // java/util/List.iterator:()Ljava/util/Iterator;
#6 = InterfaceMethodref #29.#30 // java/util/Iterator.hasNext:()Z
#7 = InterfaceMethodref #29.#31 // java/util/Iterator.next:()Ljava/lang/Object;
#8 = Fieldref #32.#33 // java/lang/System.out:Ljava/io/PrintStream;
#9 = Methodref #34.#35 // java/io/PrintStream.println:(Ljava/lang/String;)V
#10 = Class #36 // test/lambda/LambdaCode
#11 = Class #37 // java/lang/Object
#12 = Utf8 <init>
#13 = Utf8 ()V
#14 = Utf8 Code
#15 = Utf8 LineNumberTable
#16 = Utf8 main
#17 = Utf8 ([Ljava/lang/String;)V
#18 = Utf8 StackMapTable
#19 = Class #38 // java/util/Iterator
#20 = Utf8 SourceFile
#21 = Utf8 LambdaCode.java
#22 = NameAndType #12:#13 // "<init>":()V
#23 = Utf8 java/lang/String
#24 = Utf8 hello
#25 = Class #39 // java/util/Arrays
#26 = NameAndType #40:#41 // asList:([Ljava/lang/Object;)Ljava/util/List;
#27 = Class #42 // java/util/List
#28 = NameAndType #43:#44 // iterator:()Ljava/util/Iterator;
#29 = Class #38 // java/util/Iterator
#30 = NameAndType #45:#46 // hasNext:()Z
#31 = NameAndType #47:#48 // next:()Ljava/lang/Object;
#32 = Class #49 // java/lang/System
#33 = NameAndType #50:#51 // out:Ljava/io/PrintStream;
#34 = Class #52 // java/io/PrintStream
#35 = NameAndType #53:#54 // println:(Ljava/lang/String;)V
#36 = Utf8 test/lambda/LambdaCode
#37 = Utf8 java/lang/Object
#38 = Utf8 java/util/Iterator
#39 = Utf8 java/util/Arrays
#40 = Utf8 asList
#41 = Utf8 ([Ljava/lang/Object;)Ljava/util/List;
#42 = Utf8 java/util/List
#43 = Utf8 iterator
#44 = Utf8 ()Ljava/util/Iterator;
#45 = Utf8 hasNext
#46 = Utf8 ()Z
#47 = Utf8 next
#48 = Utf8 ()Ljava/lang/Object;
#49 = Utf8 java/lang/System
#50 = Utf8 out
#51 = Utf8 Ljava/io/PrintStream;
#52 = Utf8 java/io/PrintStream
#53 = Utf8 println
#54 = Utf8 (Ljava/lang/String;)V
{
public test.lambda.LambdaCode();
descriptor: ()V
flags: ACC_PUBLIC
Code:
stack=1, locals=1, args_size=1
0: aload_0
1: invokespecial #1 // Method java/lang/Object."<init>":()V
4: return
LineNumberTable:
line 15: 0
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=4, locals=3, args_size=1
0: iconst_1
1: anewarray #2 // class java/lang/String
4: dup
5: iconst_0
6: ldc #3 // String hello
8: aastore
9: invokestatic #4 // Method java/util/Arrays.asList:([Ljava/lang/Object;)Ljava/util/List;
12: invokeinterface #5, 1 // InterfaceMethod java/util/List.iterator:()Ljava/util/Iterator;
17: astore_1
18: aload_1
19: invokeinterface #6, 1 // InterfaceMethod java/util/Iterator.hasNext:()Z
24: ifeq 47
27: aload_1
28: invokeinterface #7, 1 // InterfaceMethod java/util/Iterator.next:()Ljava/lang/Object;
33: checkcast #2 // class java/lang/String
36: astore_2
37: getstatic #8 // Field java/lang/System.out:Ljava/io/PrintStream;
40: aload_2
41: invokevirtual #9 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
44: goto 18
47: return
LineNumberTable:
line 35: 0
line 36: 37
line 37: 44
line 38: 47
StackMapTable: number_of_entries = 2
frame_type = 252 /* append */
offset_delta = 18
locals = [ class java/util/Iterator ]
frame_type = 250 /* chop */
offset_delta = 28
}
y
Arrays.asList("hello").forEach(p -> {System.out.println(p);});
Código de bytes desensamblado, constantes y otra información:
Classfile LambdaCode.class
Last modified 30.05.2013; size 1262 bytes
MD5 checksum 4804e0a37b73141d5791cc39d51d649c
Compiled from "LambdaCode.java"
public class test.lambda.LambdaCode
SourceFile: "LambdaCode.java"
InnerClasses:
public static final #64= #63 of #70; //Lookup=class java/lang/invoke/MethodHandles$Lookup of class java/lang/invoke/MethodHandles
BootstrapMethods:
0: #27 invokestatic java/lang/invoke/LambdaMetafactory.metaFactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
Method arguments:
#28 invokeinterface java/util/function/Consumer.accept:(Ljava/lang/Object;)V
#29 invokestatic test/lambda/LambdaCode.lambda$0:(Ljava/lang/String;)V
#30 (Ljava/lang/String;)V
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #10.#21 // java/lang/Object."<init>":()V
#2 = Class #22 // java/lang/String
#3 = String #23 // hello
#4 = Methodref #24.#25 // java/util/Arrays.asList:([Ljava/lang/Object;)Ljava/util/List;
#5 = InvokeDynamic #0:#31 // #0:lambda$:()Ljava/util/function/Consumer;
#6 = InterfaceMethodref #32.#33 // java/util/List.forEach:(Ljava/util/function/Consumer;)V
#7 = Fieldref #34.#35 // java/lang/System.out:Ljava/io/PrintStream;
#8 = Methodref #36.#37 // java/io/PrintStream.println:(Ljava/lang/String;)V
#9 = Class #38 // test/lambda/LambdaCode
#10 = Class #39 // java/lang/Object
#11 = Utf8 <init>
#12 = Utf8 ()V
#13 = Utf8 Code
#14 = Utf8 LineNumberTable
#15 = Utf8 main
#16 = Utf8 ([Ljava/lang/String;)V
#17 = Utf8 lambda$0
#18 = Utf8 (Ljava/lang/String;)V
#19 = Utf8 SourceFile
#20 = Utf8 LambdaCode.java
#21 = NameAndType #11:#12 // "<init>":()V
#22 = Utf8 java/lang/String
#23 = Utf8 hello
#24 = Class #40 // java/util/Arrays
#25 = NameAndType #41:#42 // asList:([Ljava/lang/Object;)Ljava/util/List;
#26 = Utf8 BootstrapMethods
#27 = MethodHandle #6:#43 // invokestatic java/lang/invoke/LambdaMetafactory.metaFactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
#28 = MethodHandle #9:#44 // invokeinterface java/util/function/Consumer.accept:(Ljava/lang/Object;)V
#29 = MethodHandle #6:#45 // invokestatic test/lambda/LambdaCode.lambda$0:(Ljava/lang/String;)V
#30 = MethodType #18 // (Ljava/lang/String;)V
#31 = NameAndType #46:#47 // lambda$:()Ljava/util/function/Consumer;
#32 = Class #48 // java/util/List
#33 = NameAndType #49:#50 // forEach:(Ljava/util/function/Consumer;)V
#34 = Class #51 // java/lang/System
#35 = NameAndType #52:#53 // out:Ljava/io/PrintStream;
#36 = Class #54 // java/io/PrintStream
#37 = NameAndType #55:#18 // println:(Ljava/lang/String;)V
#38 = Utf8 test/lambda/LambdaCode
#39 = Utf8 java/lang/Object
#40 = Utf8 java/util/Arrays
#41 = Utf8 asList
#42 = Utf8 ([Ljava/lang/Object;)Ljava/util/List;
#43 = Methodref #56.#57 // java/lang/invoke/LambdaMetafactory.metaFactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
#44 = InterfaceMethodref #58.#59 // java/util/function/Consumer.accept:(Ljava/lang/Object;)V
#45 = Methodref #9.#60 // test/lambda/LambdaCode.lambda$0:(Ljava/lang/String;)V
#46 = Utf8 lambda$
#47 = Utf8 ()Ljava/util/function/Consumer;
#48 = Utf8 java/util/List
#49 = Utf8 forEach
#50 = Utf8 (Ljava/util/function/Consumer;)V
#51 = Utf8 java/lang/System
#52 = Utf8 out
#53 = Utf8 Ljava/io/PrintStream;
#54 = Utf8 java/io/PrintStream
#55 = Utf8 println
#56 = Class #61 // java/lang/invoke/LambdaMetafactory
#57 = NameAndType #62:#66 // metaFactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
#58 = Class #67 // java/util/function/Consumer
#59 = NameAndType #68:#69 // accept:(Ljava/lang/Object;)V
#60 = NameAndType #17:#18 // lambda$0:(Ljava/lang/String;)V
#61 = Utf8 java/lang/invoke/LambdaMetafactory
#62 = Utf8 metaFactory
#63 = Class #71 // java/lang/invoke/MethodHandles$Lookup
#64 = Utf8 Lookup
#65 = Utf8 InnerClasses
#66 = Utf8 (Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
#67 = Utf8 java/util/function/Consumer
#68 = Utf8 accept
#69 = Utf8 (Ljava/lang/Object;)V
#70 = Class #72 // java/lang/invoke/MethodHandles
#71 = Utf8 java/lang/invoke/MethodHandles$Lookup
#72 = Utf8 java/lang/invoke/MethodHandles
{
public test.lambda.LambdaCode();
descriptor: ()V
flags: ACC_PUBLIC
Code:
stack=1, locals=1, args_size=1
0: aload_0
1: invokespecial #1 // Method java/lang/Object."<init>":()V
4: return
LineNumberTable:
line 15: 0
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=4, locals=1, args_size=1
0: iconst_1
1: anewarray #2 // class java/lang/String
4: dup
5: iconst_0
6: ldc #3 // String hello
8: aastore
9: invokestatic #4 // Method java/util/Arrays.asList:([Ljava/lang/Object;)Ljava/util/List;
12: invokedynamic #5, 0 // InvokeDynamic #0:lambda$:()Ljava/util/function/Consumer;
17: invokeinterface #6, 2 // InterfaceMethod java/util/List.forEach:(Ljava/util/function/Consumer;)V
22: return
LineNumberTable:
line 28: 0
line 38: 22
}
El archivo de clase generado por el compilador es más complicado y más grande (771b frente a 1262b) para el ejemplo de Lambda.
Loop.times(5, () -> {
System.out.println("looping");
});
¿A cuál de estos sería efectivamente compilar?
for(int i = 0; i < 5; i++)
System.out.println("looping");
o algo así como
new CallableInterfaceImpl(){
public void call(){
for(int i = 0; i < 5; i++)
System.out.println("looping");
}
}.call();
¿Reemplazaría (tipo de línea) o crearía una clase anónima?