Jack, translated lambda expression, doesn't take a more efficient approach when minSdkVersion is set to 24

Question

I am currently looking at the bytecode that the compiler jackgenerates for lambda expressions.

As an example, take the following simple Java class:

public class ForEach {
    public static void main (String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("hello");
        list.forEach(s -> System.out.println(s));
    }
}

When using JDK 1.8, javacit generates the following bytecode:

public class ForEach
  minor version: 0
  major version: 52
  flags: ACC_PUBLIC, ACC_SUPER
{

// .. redacted

  public static void main(java.lang.String[]);
    descriptor: ([Ljava/lang/String;)V
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=2, locals=2, args_size=1
         0: new           #2                  // class java/util/ArrayList
         3: dup
         4: invokespecial #3                  // Method java/util/ArrayList."<init>":()V
         7: astore_1
         8: aload_1
         9: ldc           #4                  // String hello
        11: invokevirtual #5                  // Method java/util/ArrayList.add:(Ljava/lang/Object;)Z
        14: pop
        15: aload_1
        16: invokedynamic #6,  0              // InvokeDynamic #0:accept:()Ljava/util/function/Consumer;
        21: invokevirtual #7                  // Method java/util/ArrayList.forEach:(Ljava/util/function/Consumer;)V
        24: return

  private static void lambda$main$0(java.lang.String);
    descriptor: (Ljava/lang/String;)V
    flags: ACC_PRIVATE, ACC_STATIC, ACC_SYNTHETIC
    Code:
      stack=2, locals=1, args_size=1
         0: getstatic     #8                  // Field java/lang/System.out:Ljava/io/PrintStream;
         3: aload_0
         4: invokevirtual #9                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
         7: return
      LineNumberTable:
        line 7: 0
}
BootstrapMethods:
  0: #27 invokestatic java/lang/invoke/LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
    Method arguments:
      #28 (Ljava/lang/Object;)V
      #29 invokestatic ForEach.lambda$main$0:(Ljava/lang/String;)V
      #30 (Ljava/lang/String;)V

As for the documentation , translating a lambda expression into bytecode, performed by generating invokedynamic call siteon line 16, and by converting the body of the lambda expression to a static method.

Now let's talk about jack. Typically, when compiling a lambda with minSdkVersionless than 24, the compiler jackgenerates an anonymous class - for backward compatibility with previous versions based on 1.6 / 1.7.

, minSdkVersion ​​ 24?
, lambda- ( Java ) jack Android:

public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ArrayList<String> list = new ArrayList<>();
        list.add("hello");
        list.forEach(s -> System.out.println(s));
    }
}

, jack / (- JVM invokedynamic call site -), Android 7.0 1.8.
, invokedynamic Dalvik, ART, , . lambda Android - .

- :

Class #48            -
  Class descriptor  : 'Linfo/osom/java8demo/MainActivity;'

// .. redacted

  Virtual methods   -
    #0              : (in Linfo/osom/java8demo/MainActivity;)
      name          : 'onCreate'
      type          : '(Landroid/os/Bundle;)V'
      access        : 0x0004 (PROTECTED)
[0014a0] info.osom.java8demo.MainActivity.onCreate:(Landroid/os/Bundle;)V
0000: invoke-super {v2, v3}, Landroid/app/Activity;.onCreate:(Landroid/os/Bundle;)V // method@0001
0003: const/high16 v0, #int 2130903040 // #7f03
0005: invoke-virtual {v2, v0}, Linfo/osom/java8demo/MainActivity;.setContentView:(I)V // method@0020
0008: new-instance v0, Ljava/util/ArrayList; // type@005b
000a: invoke-direct {v0}, Ljava/util/ArrayList;.<init>:()V // method@003f
000d: const-string/jumbo v1, "hello" // string@000000b9
0010: invoke-virtual {v0, v1}, Ljava/util/ArrayList;.add:(Ljava/lang/Object;)Z // method@0041
0013: new-instance v1, Linfo/osom/java8demo/MainActivity$-void_onCreate_android_os_Bundle_savedInstanceState_LambdaImpl0; // type@003c
0015: invoke-direct {v1}, Linfo/osom/java8demo/MainActivity$-void_onCreate_android_os_Bundle_savedInstanceState_LambdaImpl0;.<init>:()V // method@001b
0018: invoke-virtual {v0, v1}, Ljava/util/ArrayList;.forEach:(Ljava/util/function/Consumer;)V // method@0042
001b: return-void

// .. redacted

jack - - , , JVM invokedynamic ?