Optimization of Android Internal classes

There is an article on performance in the developer.android.com documentation that mentions the use of internal classes. The article suggests "use package access permissions instead of private access for private internal classes",

This is to say that when an internal class visits a member or method of an external class, it is assumed that the inner class is private and that the members of the outer class are private, then the compiler adds a static method to the inner class.

Is that really the case? Just have a try before you know.

Let's use a simple sample to test:

public class One {private int a;private class B{public int Geta () {return A;}}}

The top code creates a private inner class B for one, and B has a way to access private member A in one. We have compiled the above code into a Dex file and exported the program's instruction code and class information.

The results of the export are as follows:

Processing ' one.dex ' ...  Opened ' One.dex ', Dex version ' 035 ' Class #0-class descriptor: ' lone$b; '  Access flags:0x0000 () superclass: ' Ljava/lang/object; ' Interfaces-static fields-instance fields-#0: (in lone$b;) Name: ' This      $ ' type: ' LOne; ' ACCESS:0X1010 (FINAL synthetic) Direct methods-#0: (in lone$b;) Name: ' < Init> ' type: ' (LOne;) V ' access:0x10002 (PRIVATE CONSTRUCTOR) Code-reg                                        Isters:2 ins:2 outs:1 Insns size:6 16-bit code units0001a0: | [0001a0] one.b.<init>:(LOne;) v0001b0:5b01 0000 |0000:iput-object v1, v0, lone$b;. This$0:lone; [email protected]0001b4:7010 0400 0000 |0002:invoke-direct {V0}, ljava/lang/object;. <init>:() V//[email protected]0001ba:0e00 |0005:return-void catches: (none)   positions:0x0000 line=7 locals:0x0000-0x0006 reg=0 this lone$b;        Virtual methods-#0: (in lone$b;) name: ' Geta ' type: ' () I ' access : 0x0001 (public) Code-registers:2 ins:1 outs:1 ins NS Size:7 16-bit code UNITS0001BC: | [0001BC] One.b.geta: () i0001cc:5410 0000 |0000:iget-object v0, v1, lone$b;. This$0:lone; [email protected]0001d0:7110 0300 0000 |0002:invoke-static {V0}, LOne;. Access$0: (LOne;) I//[email protected]0001d6:0a00 |0005:move-result v00001d8:0f0    0 |0006:return V0 catches: (none) positions : 0x0000 line=10 locals:0x0000-0x0007 reg=1 this lone$b;  Source_file_idx:10 (One.java) Class #1-class descriptor: ' LOne; '  Access flags:0x0001 (public) Superclass: ' Ljava/lang/object; '      Interfaces-static fields-instance fields-#0: (in LOne;) name: ' A '           Type: ' I ' access:0x0002 (PRIVATE) Direct methods-#0: (in LOne;) name          : ' <init> ' type: ' () V ' access:0x10001 (public CONSTRUCTOR) code                                        -Registers:1 ins:1 outs:1 Insns size:4 16-bit code UNITS0001DC: | [0001DC] one.<init>:() v0001ec:7010 0400 0000 |0000:invoke-direct {V0}, ljava/lang/object;. <init>:() V//[email protected]0001f2:0e00 |0003:Return-void catches: (none) positions:0x0000 line=3 locals:0x0000-0     x0004 reg=0 this LOne; #1: (in LOne;) name: ' access$0 ' type: ' (LOne;) I ' access:0x1008 ( STATIC synthetic) code-registers:2 ins:1 outs:0 Insns siz E:3 16-bit Code UNITS0001F4: | [0001f4] one.access$0: (LOne;) i000204:5210 0100 |0000:iget v0, v1, LOne;.      A:I//[email protected]000208:0f00 |0002:return V0 catches: (none) positions:0x0000 line=5 locals:virtual methods-source_file_idx:10 (One.java)

Ha See there is not one more method, and our source code is not.

One.access$0: (LOne;) I

Now let's change the source code

public class One {private int a;class b{public int Geta () {return A;}}}

Then in the compilation, export:

Processing ' one.dex ' ...  Opened ' One.dex ', Dex version ' 035 ' Class #0-class descriptor: ' lone$b; '  Access flags:0x0000 () superclass: ' Ljava/lang/object; ' Interfaces-static fields-instance fields-#0: (in lone$b;) Name: ' This      $ ' type: ' LOne; ' ACCESS:0X1010 (FINAL synthetic) Direct methods-#0: (in lone$b;) Name: ' <     Init> ' type: ' (LOne;) V ' access:0x10000 (CONSTRUCTOR) code-registers                                        : 2 ins:2 outs:1 Insns size:6 16-bit code units0001a0: | [0001a0] one.b.<init>:(LOne;) v0001b0:5b01 0000 |0000:iput-object v1, v0, lone$b;. This$0:lone; [email protected]0001b4:7010 0400 0000 |0002:invoke-direct {V0}, ljava/lang/object;. <init>:() V//[Email protected]0001ba:0e00 |0005:return-void catches: (none) po   sitions:0x0000 line=7 locals:0x0000-0x0006 reg=0 this lone$b;        Virtual methods-#0: (in lone$b;) name: ' Geta ' type: ' () I ' access : 0x0001 (public) Code-registers:2 ins:1 outs:1 ins NS Size:7 16-bit code UNITS0001BC: | [0001BC] One.b.geta: () i0001cc:5410 0000 |0000:iget-object v0, v1, lone$b;. This$0:lone; [email protected]0001d0:7110 0300 0000 |0002:invoke-static {V0}, LOne;. Access$0: (LOne;) I//[email protected]0001d6:0a00 |0005:move-result v00001d8:0f0      0 |0006:return V0 catches: (none) Positions:   0x0000 line=10 locals:0x0000-0x0007 reg=1 this lone$b;  Source_file_idx:10 (One.java) Class #1-class descriptor: ' LOne; '  Access flags:0x0001 (public) Superclass: ' Ljava/lang/object; '      Interfaces-static fields-instance fields-#0: (in LOne;) name: ' A '           Type: ' I ' access:0x0002 (PRIVATE) Direct methods-#0: (in LOne;) name          : ' <init> ' type: ' () V ' access:0x10001 (public CONSTRUCTOR) code                                        -Registers:1 ins:1 outs:1 Insns size:4 16-bit code UNITS0001DC: | [0001DC] one.<init>:() v0001ec:7010 0400 0000 |0000:invoke-direct {V0}, ljava/lang/object;. <init>:() V//[email protected]0001f2:0e00 |0003:return-vOID catches: (none) positions:0x0000 line=3 locals:0x0000-0x0004 re     G=0 this LOne; #1: (in LOne;) name: ' access$0 ' type: ' (LOne;) I ' access:0x1008 ( STATIC synthetic) code-registers:2 ins:1 outs:0 Insns siz E:3 16-bit Code UNITS0001F4: | [0001f4] one.access$0: (LOne;) i000204:5210 0100 |0000:iget v0, v1, LOne;.      A:I//[email protected]000208:0f00 |0002:return V0 catches: (none) positions:0x0000 line=5 locals:virtual methods-source_file_idx:10 (One.java)

There are still additional methods.

One.access$0: (LOne;) I

We're under change.

public class One {int a;class b{public int Geta () {return A;}}}

In the compilation export

Processing ' one.dex ' ...  Opened ' One.dex ', Dex version ' 035 ' Class #0-class descriptor: ' lone$b; '  Access flags:0x0000 () superclass: ' Ljava/lang/object; ' Interfaces-static fields-instance fields-#0: (in lone$b;) Name: ' This      $ ' type: ' LOne; ' ACCESS:0X1010 (FINAL synthetic) Direct methods-#0: (in lone$b;) Name: ' <     Init> ' type: ' (LOne;) V ' access:0x10000 (CONSTRUCTOR) code-registers                                        : 2 ins:2 outs:1 Insns size:6 16-bit code units000184: | [000184] one.b.<init>:(LOne;) v000194:5b01 0000 |0000:iput-object v1, v0, lone$b;. This$0:lone; [email protected]000198:7010 0300 0000 |0002:invoke-direct {V0}, ljava/lang/object;. <init>:() V//[Email protected]00019e:0e00 |0005:return-void catches: (none) po   sitions:0x0000 line=7 locals:0x0000-0x0006 reg=0 this lone$b;        Virtual methods-#0: (in lone$b;) name: ' Geta ' type: ' () I ' access : 0x0001 (public) Code-registers:2 ins:1 outs:0 ins NS Size:5 16-bit code units0001a0: | [0001a0] One.b.geta: () i0001b0:5410 0000 |0000:iget-object v0, v1, lone$b;. This$0:lone; [email protected]0001b4:5200 0100 |0002:iget v0, V0, LOne;.      A:I//[email protected]0001b8:0f00 |0004:return V0 catches: (none)   positions:0x0000 line=10 locals:0x0000-0x0005 reg=1 this lone$b; SourcE_file_idx:9 (One.java) Class #1-class descriptor: ' LOne; '  Access flags:0x0001 (public) Superclass: ' Ljava/lang/object; '      Interfaces-static fields-instance fields-#0: (in LOne;) name: ' A '          Type: ' I ' access:0x0000 () Direct methods-#0: (in LOne;) name      : ' <init> ' type: ' () V ' access:0x10001 (public CONSTRUCTOR) code-                                        Registers:1 ins:1 outs:1 Insns size:4 16-bit code UNITS0001BC: | [0001BC] one.<init>:() v0001cc:7010 0300 0000 |0000:invoke-direct {V0}, ljava/lang/object;.       <init>:() V//[email protected]0001d2:0e00 |0003:return-void catches  : (none) positions:0x0000 line=3 locals:       0x0000-0x0004 reg=0 this LOne; Virtual Methods-source_file_idx:9 (One.java)

No additional methods are already in the way.

Assuming that the members of the external class are packet access, the inner class is private and does not produce an additional method.

Internal classes The access to the members of the external class is not directly accessible to private members, the compiler will add additional auxiliary methods, avoid the method is to change the members of the external class to access the package, the document also mentions that this will to some extent destroy

Packaging.

Optimization of Android Internal classes