恷弌 Hello World! チャレンジ
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The document discusses minimizing the size of a Java "Hello World" class file. It begins by creating a simple "Hello World" Java class that prints the message, which compiles to a 408 byte class file. The document then explores using Jasmin assembler to reduce the size to 303 bytes by removing the constructor. It analyzes the class file format and constant pool, identifying the constant pool as the dominant size component in small programs. The document proposes ways to further minimize the class file size by reducing the constant pool, such as removing the SourceFile attribute.
![まずは Java で
class J {
public static void main(String args[]) {
System.out.println("Hello World!");
}
}
-rw-r--r-- 1 kawachi staff 408 Mar 3 23:07 J.class
javac して´
408 bytes](https://image.slidesharecdn.com/minhelloworld-150307015125-conversion-gate01/85/Hello-World-3-320.jpg)
![javap -c でみてみる
$ javap -c J.class
Compiled from "A.java"
class J {
J();
Code:
0: aload_0
1: invokespecial #1 // Method java/lang/
Object."<init>":()V
4: return
public static void main(java.lang.String[]);
Code:
0: getstatic #2 // Field java/lang/
System.out:Ljava/io/PrintStream;
3: ldc #3 // String Hello
World!
5: invokevirtual #4 // Method java/io/
PrintStream.println:(Ljava/lang/String;)V
8: return
}
コンストラクタ
main()
Hello World!にコンストラクタは勣らない](https://image.slidesharecdn.com/minhelloworld-150307015125-conversion-gate01/85/Hello-World-4-320.jpg)
![.class ファイルのiみ圭
Java Virtual Machine Speci?cation,
4. The class File Format
ClassFile {
u4 magic;
u2 minor_version;
u2 major_version;
u2 constant_pool_count;
cp_info constant_pool[constant_pool_count-1];
u2 access_flags;
u2 this_class;
u2 super_class;
u2 interfaces_count;
u2 interfaces[interfaces_count];
u2 fields_count;
field_info fields[fields_count];
u2 methods_count;
method_info methods[methods_count];
u2 attributes_count;
attribute_info attributes[attributes_count];
}
枠^に4bytes マジック
肝の2bytesが?
マイナ`バ`ジョン
參和揖に](https://image.slidesharecdn.com/minhelloworld-150307015125-conversion-gate01/85/Hello-World-7-320.jpg)
恷弌 Hello World! チャレンジ
- 1. 恷弌 Hello World!? チャレンジ #i紅Java 2015-03-07 pLucky, Inc. @kawachi 采坪 括
- 2. お} Hello World! を咫忖する? .class ファイルを? どこまで弌さくできるか
- 3. まずは Java で class J { public static void main(String args[]) { System.out.println("Hello World!"); } } -rw-r--r-- 1 kawachi staff 408 Mar 3 23:07 J.class javac して´ 408 bytes
- 4. javap -c でみてみる $ javap -c J.class Compiled from "A.java" class J { J(); Code: 0: aload_0 1: invokespecial #1 // Method java/lang/ Object."<init>":()V 4: return public static void main(java.lang.String[]); Code: 0: getstatic #2 // Field java/lang/ System.out:Ljava/io/PrintStream; 3: ldc #3 // String Hello World! 5: invokevirtual #4 // Method java/io/ PrintStream.println:(Ljava/lang/String;)V 8: return } コンストラクタ main() Hello World!にコンストラクタは勣らない
- 5. Jasmin でトライ JVM byte code 喘アセンブラ .class public M .super java/lang/Object .method public static main([Ljava/lang/String;)V .limit stack 2 getstatic java/lang/System/out Ljava/io/PrintStream; ldc "Hello World!" invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V return .end method jasmin M.j して´ -rw-r--r-- 1 kawachi staff 303 Mar 3 23:13 M.class 303 bytes (74.2%)408 bytes ★ main() だけ
- 6. バイナリみてみる $ hexdump -C M.class 00000000 ca fe ba be 00 03 00 2d 00 18 0c 00 14 00 17 01 |.......-........| 00000010 00 16 28 5b 4c 6a 61 76 61 2f 6c 61 6e 67 2f 53 |..([Ljava/lang/S| 00000020 74 72 69 6e 67 3b 29 56 01 00 10 6a 61 76 61 2f |tring;)V...java/| 00000030 6c 61 6e 67 2f 4f 62 6a 65 63 74 07 00 03 01 00 |lang/Object.....| 00000040 0c 48 65 6c 6c 6f 20 57 6f 72 6c 64 21 07 00 0f |.Hello World!...| 00000050 08 00 05 07 00 12 01 00 04 43 6f 64 65 01 00 04 |.........Code...| 00000060 6d 61 69 6e 09 00 08 00 01 01 00 01 4d 01 00 0a |main........M...| 00000070 53 6f 75 72 63 65 46 69 6c 65 0c 00 10 00 15 01 |SourceFile......| 00000080 00 13 6a 61 76 61 2f 69 6f 2f 50 72 69 6e 74 53 |..java/io/PrintS| 00000090 74 72 65 61 6d 01 00 07 70 72 69 6e 74 6c 6e 07 |tream...println.| 000000a0 00 0c 01 00 10 6a 61 76 61 2f 6c 61 6e 67 2f 53 |.....java/lang/S| 000000b0 79 73 74 65 6d 0a 00 06 00 0e 01 00 03 6f 75 74 |ystem........out| 000000c0 01 00 15 28 4c 6a 61 76 61 2f 6c 61 6e 67 2f 53 |...(Ljava/lang/S| 000000d0 74 72 69 6e 67 3b 29 56 01 00 03 4d 2e 6a 01 00 |tring;)V...M.j..| 000000e0 15 4c 6a 61 76 61 2f 69 6f 2f 50 72 69 6e 74 53 |.Ljava/io/PrintS| 000000f0 74 72 65 61 6d 3b 00 21 00 11 00 04 00 00 00 00 |tream;.!........| 00000100 00 01 00 09 00 0a 00 02 00 01 00 09 00 00 00 15 |................| 00000110 00 02 00 01 00 00 00 09 b2 00 0b 12 07 b6 00 13 |................| 00000120 b1 00 00 00 00 00 01 00 0d 00 00 00 02 00 16 |...............| 0000012f う`ん。わからん
- 7. .class ファイルのiみ圭 Java Virtual Machine Speci?cation, 4. The class File Format ClassFile { u4 magic; u2 minor_version; u2 major_version; u2 constant_pool_count; cp_info constant_pool[constant_pool_count-1]; u2 access_flags; u2 this_class; u2 super_class; u2 interfaces_count; u2 interfaces[interfaces_count]; u2 fields_count; field_info fields[fields_count]; u2 methods_count; method_info methods[methods_count]; u2 attributes_count; attribute_info attributes[attributes_count]; } 枠^に4bytes マジック 肝の2bytesが? マイナ`バ`ジョン 參和揖に
- 8. iめる、iめるぞ $ hexdump -C M.class 00000000 ca fe ba be 00 03 00 2d 00 18 0c 00 14 00 17 01 |.......-........| 00000010 00 16 28 5b 4c 6a 61 76 61 2f 6c 61 6e 67 2f 53 |..([Ljava/lang/S| 00000020 74 72 69 6e 67 3b 29 56 01 00 10 6a 61 76 61 2f |tring;)V...java/| 00000030 6c 61 6e 67 2f 4f 62 6a 65 63 74 07 00 03 01 00 |lang/Object.....| 00000040 0c 48 65 6c 6c 6f 20 57 6f 72 6c 64 21 07 00 0f |.Hello World!...| 00000050 08 00 05 07 00 12 01 00 04 43 6f 64 65 01 00 04 |.........Code...| 00000060 6d 61 69 6e 09 00 08 00 01 01 00 01 4d 01 00 0a |main........M...| 00000070 53 6f 75 72 63 65 46 69 6c 65 0c 00 10 00 15 01 |SourceFile......| 00000080 00 13 6a 61 76 61 2f 69 6f 2f 50 72 69 6e 74 53 |..java/io/PrintS| 00000090 74 72 65 61 6d 01 00 07 70 72 69 6e 74 6c 6e 07 |tream...println.| 000000a0 00 0c 01 00 10 6a 61 76 61 2f 6c 61 6e 67 2f 53 |.....java/lang/S| 000000b0 79 73 74 65 6d 0a 00 06 00 0e 01 00 03 6f 75 74 |ystem........out| 000000c0 01 00 15 28 4c 6a 61 76 61 2f 6c 61 6e 67 2f 53 |...(Ljava/lang/S| 000000d0 74 72 69 6e 67 3b 29 56 01 00 03 4d 2e 6a 01 00 |tring;)V...M.j..| 000000e0 15 4c 6a 61 76 61 2f 69 6f 2f 50 72 69 6e 74 53 |.Ljava/io/PrintS| 000000f0 74 72 65 61 6d 3b 00 21 00 11 00 04 00 00 00 00 |tream;.!........| 00000100 00 01 00 09 00 0a 00 02 00 01 00 09 00 00 00 15 |................| 00000110 00 02 00 01 00 00 00 09 b2 00 0b 12 07 b6 00 13 |................| 00000120 b1 00 00 00 00 00 01 00 0d 00 00 00 02 00 16 |...............| 0000012f
- 9. .class は constant pool が9護 $ hexdump -C M.class 00000000 ca fe ba be 00 03 00 2d 00 18 0c 00 14 00 17 01 |.......-........| 00000010 00 16 28 5b 4c 6a 61 76 61 2f 6c 61 6e 67 2f 53 |..([Ljava/lang/S| 00000020 74 72 69 6e 67 3b 29 56 01 00 10 6a 61 76 61 2f |tring;)V...java/| 00000030 6c 61 6e 67 2f 4f 62 6a 65 63 74 07 00 03 01 00 |lang/Object.....| 00000040 0c 48 65 6c 6c 6f 20 57 6f 72 6c 64 21 07 00 0f |.Hello World!...| 00000050 08 00 05 07 00 12 01 00 04 43 6f 64 65 01 00 04 |.........Code...| 00000060 6d 61 69 6e 09 00 08 00 01 01 00 01 4d 01 00 0a |main........M...| 00000070 53 6f 75 72 63 65 46 69 6c 65 0c 00 10 00 15 01 |SourceFile......| 00000080 00 13 6a 61 76 61 2f 69 6f 2f 50 72 69 6e 74 53 |..java/io/PrintS| 00000090 74 72 65 61 6d 01 00 07 70 72 69 6e 74 6c 6e 07 |tream...println.| 000000a0 00 0c 01 00 10 6a 61 76 61 2f 6c 61 6e 67 2f 53 |.....java/lang/S| 000000b0 79 73 74 65 6d 0a 00 06 00 0e 01 00 03 6f 75 74 |ystem........out| 000000c0 01 00 15 28 4c 6a 61 76 61 2f 6c 61 6e 67 2f 53 |...(Ljava/lang/S| 000000d0 74 72 69 6e 67 3b 29 56 01 00 03 4d 2e 6a 01 00 |tring;)V...M.j..| 000000e0 15 4c 6a 61 76 61 2f 69 6f 2f 50 72 69 6e 74 53 |.Ljava/io/PrintS| 000000f0 74 72 65 61 6d 3b 00 21 00 11 00 04 00 00 00 00 |tream;.!........| 00000100 00 01 00 09 00 0a 00 02 00 01 00 09 00 00 00 15 |................| 00000110 00 02 00 01 00 00 00 09 b2 00 0b 12 07 b6 00 13 |................| 00000120 b1 00 00 00 00 00 01 00 0d 00 00 00 02 00 16 |...............| 0000012f Constant pool main()
- 10. constant pool ? 玉いプログラムでは constant pool が屶塘議サイズ ? 猟忖双協方とか、クラス歌孚とかが秘ってる ? constant pool を泌採にるかが掫
- 11. pポイント1: SourceFile 奉來 $ hexdump -C M.class 00000000 ca fe ba be 00 03 00 2d 00 18 0c 00 14 00 17 01 |.......-........| 00000010 00 16 28 5b 4c 6a 61 76 61 2f 6c 61 6e 67 2f 53 |..([Ljava/lang/S| 00000020 74 72 69 6e 67 3b 29 56 01 00 10 6a 61 76 61 2f |tring;)V...java/| 00000030 6c 61 6e 67 2f 4f 62 6a 65 63 74 07 00 03 01 00 |lang/Object.....| 00000040 0c 48 65 6c 6c 6f 20 57 6f 72 6c 64 21 07 00 0f |.Hello World!...| 00000050 08 00 05 07 00 12 01 00 04 43 6f 64 65 01 00 04 |.........Code...| 00000060 6d 61 69 6e 09 00 08 00 01 01 00 01 4d 01 00 0a |main........M...| 00000070 53 6f 75 72 63 65 46 69 6c 65 0c 00 10 00 15 01 |SourceFile......| 00000080 00 13 6a 61 76 61 2f 69 6f 2f 50 72 69 6e 74 53 |..java/io/PrintS| 00000090 74 72 65 61 6d 01 00 07 70 72 69 6e 74 6c 6e 07 |tream...println.| 000000a0 00 0c 01 00 10 6a 61 76 61 2f 6c 61 6e 67 2f 53 |.....java/lang/S| 000000b0 79 73 74 65 6d 0a 00 06 00 0e 01 00 03 6f 75 74 |ystem........out| 000000c0 01 00 15 28 4c 6a 61 76 61 2f 6c 61 6e 67 2f 53 |...(Ljava/lang/S| 000000d0 74 72 69 6e 67 3b 29 56 01 00 03 4d 2e 6a 01 00 |tring;)V...M.j..| 000000e0 15 4c 6a 61 76 61 2f 69 6f 2f 50 72 69 6e 74 53 |.Ljava/io/PrintS| 000000f0 74 72 65 61 6d 3b 00 21 00 11 00 04 00 00 00 00 |tream;.!........| 00000100 00 01 00 09 00 0a 00 02 00 01 00 09 00 00 00 15 |................| 00000110 00 02 00 01 00 00 00 09 b2 00 0b 12 07 b6 00 13 |................| 00000120 b1 00 00 00 00 00 01 00 0d 00 00 00 02 00 16 |...............| 0000012f SourceFile 奉來。oくても咾 ＾SourceFile￣ ＾M.j￣
- 12. pポイント2:徭クラス兆 $ hexdump -C M.class 00000000 ca fe ba be 00 03 00 2d 00 18 0c 00 14 00 17 01 |.......-........| 00000010 00 16 28 5b 4c 6a 61 76 61 2f 6c 61 6e 67 2f 53 |..([Ljava/lang/S| 00000020 74 72 69 6e 67 3b 29 56 01 00 10 6a 61 76 61 2f |tring;)V...java/| 00000030 6c 61 6e 67 2f 4f 62 6a 65 63 74 07 00 03 01 00 |lang/Object.....| 00000040 0c 48 65 6c 6c 6f 20 57 6f 72 6c 64 21 07 00 0f |.Hello World!...| 00000050 08 00 05 07 00 12 01 00 04 43 6f 64 65 01 00 04 |.........Code...| 00000060 6d 61 69 6e 09 00 08 00 01 01 00 01 4d 01 00 0a |main........M...| 00000070 53 6f 75 72 63 65 46 69 6c 65 0c 00 10 00 15 01 |SourceFile......| 00000080 00 13 6a 61 76 61 2f 69 6f 2f 50 72 69 6e 74 53 |..java/io/PrintS| 00000090 74 72 65 61 6d 01 00 07 70 72 69 6e 74 6c 6e 07 |tream...println.| 000000a0 00 0c 01 00 10 6a 61 76 61 2f 6c 61 6e 67 2f 53 |.....java/lang/S| 000000b0 79 73 74 65 6d 0a 00 06 00 0e 01 00 03 6f 75 74 |ystem........out| 000000c0 01 00 15 28 4c 6a 61 76 61 2f 6c 61 6e 67 2f 53 |...(Ljava/lang/S| 000000d0 74 72 69 6e 67 3b 29 56 01 00 03 4d 2e 6a 01 00 |tring;)V...M.j..| 000000e0 15 4c 6a 61 76 61 2f 69 6f 2f 50 72 69 6e 74 53 |.Ljava/io/PrintS| 000000f0 74 72 65 61 6d 3b 00 21 00 11 00 04 00 00 00 00 |tream;.!........| 00000100 00 01 00 09 00 0a 00 02 00 01 00 09 00 00 00 15 |................| 00000110 00 02 00 01 00 00 00 09 b2 00 0b 12 07 b6 00 13 |................| 00000120 b1 00 00 00 00 00 01 00 0d 00 00 00 02 00 16 |...............| 0000012f ＾M￣クラス歌孚 this_class ＾Code￣? (メソッドの嶄附を燕Fするために駅ず贋壓) クラス兆を Code にすれば ＾M￣ をせる
- 14. pポイント3:Hクラス $ hexdump -C M.class 00000000 ca fe ba be 00 03 00 2d 00 18 0c 00 14 00 17 01 |.......-........| 00000010 00 16 28 5b 4c 6a 61 76 61 2f 6c 61 6e 67 2f 53 |..([Ljava/lang/S| 00000020 74 72 69 6e 67 3b 29 56 01 00 10 6a 61 76 61 2f |tring;)V...java/| 00000030 6c 61 6e 67 2f 4f 62 6a 65 63 74 07 00 03 01 00 |lang/Object.....| 00000040 0c 48 65 6c 6c 6f 20 57 6f 72 6c 64 21 07 00 0f |.Hello World!...| 00000050 08 00 05 07 00 12 01 00 04 43 6f 64 65 01 00 04 |.........Code...| 00000060 6d 61 69 6e 09 00 08 00 01 01 00 01 4d 01 00 0a |main........M...| 00000070 53 6f 75 72 63 65 46 69 6c 65 0c 00 10 00 15 01 |SourceFile......| 00000080 00 13 6a 61 76 61 2f 69 6f 2f 50 72 69 6e 74 53 |..java/io/PrintS| 00000090 74 72 65 61 6d 01 00 07 70 72 69 6e 74 6c 6e 07 |tream...println.| 000000a0 00 0c 01 00 10 6a 61 76 61 2f 6c 61 6e 67 2f 53 |.....java/lang/S| 000000b0 79 73 74 65 6d 0a 00 06 00 0e 01 00 03 6f 75 74 |ystem........out| 000000c0 01 00 15 28 4c 6a 61 76 61 2f 6c 61 6e 67 2f 53 |...(Ljava/lang/S| 000000d0 74 72 69 6e 67 3b 29 56 01 00 03 4d 2e 6a 01 00 |tring;)V...M.j..| 000000e0 15 4c 6a 61 76 61 2f 69 6f 2f 50 72 69 6e 74 53 |.Ljava/io/PrintS| 000000f0 74 72 65 61 6d 3b 00 21 00 11 00 04 00 00 00 00 |tream;.!........| 00000100 00 01 00 09 00 0a 00 02 00 01 00 09 00 00 00 15 |................| 00000110 00 02 00 01 00 00 00 09 b2 00 0b 12 07 b6 00 13 |................| 00000120 b1 00 00 00 00 00 01 00 0d 00 00 00 02 00 16 |...............| 0000012f ＾java/lang/Object￣ クラス歌孚 super_class Hクラスを PrintStream にすれば ＾java/lang/Object￣ とそのクラス歌孚がれる? (java/lang/System は ?nal なのでダメ ＾java/io/PrintStream￣ (System.out の歌孚で旋喘)
- 15. バイナリエディタできQえ $ hexdump -C Code.class 00000000 ca fe ba be 00 03 00 2d 00 13 0c 00 10 00 12 01 |.......-........| 00000010 00 16 28 5b 4c 6a 61 76 61 2f 6c 61 6e 67 2f 53 |..([Ljava/lang/S| 00000020 74 72 69 6e 67 3b 29 56 01 00 0c 48 65 6c 6c 6f |tring;)V...Hello| 00000030 20 57 6f 72 6c 64 21 07 00 0b 08 00 03 07 00 0e | World!.........| 00000040 01 00 04 43 6f 64 65 01 00 04 6d 61 69 6e 09 00 |...Code...main..| 00000050 06 00 01 0c 00 0c 00 11 01 00 13 6a 61 76 61 2f |...........java/| 00000060 69 6f 2f 50 72 69 6e 74 53 74 72 65 61 6d 01 00 |io/PrintStream..| 00000070 07 70 72 69 6e 74 6c 6e 07 00 07 01 00 10 6a 61 |.println......ja| 00000080 76 61 2f 6c 61 6e 67 2f 53 79 73 74 65 6d 0a 00 |va/lang/System..| 00000090 04 00 0a 01 00 03 6f 75 74 01 00 15 28 4c 6a 61 |......out...(Lja| 000000a0 76 61 2f 6c 61 6e 67 2f 53 74 72 69 6e 67 3b 29 |va/lang/String;)| 000000b0 56 01 00 15 4c 6a 61 76 61 2f 69 6f 2f 50 72 69 |V...Ljava/io/Pri| 000000c0 6e 74 53 74 72 65 61 6d 3b 00 21 00 0d 00 04 00 |ntStream;.!.....| 000000d0 00 00 00 00 01 00 09 00 08 00 02 00 01 00 07 00 |................| 000000e0 00 00 15 00 02 00 01 00 00 00 09 b2 00 09 12 05 |................| 000000f0 b6 00 0f b1 00 00 00 00 00 00 |..........| 000000fa 250 bytes (61.2%)408 bytes ★ constant pool count 0x18★0x13
- 16. 暴の基え Hello World! を咫忖する? .class ファイルを? どこまで弌さくできるか 250 bytes
- 17. まとめ ? JVM碧とバイナリエディタがあればY[べる ? ｼをg`えると噸粁ないエラ`がられる ? .class iめると javap の竃薦にHしみがイ ? チャレンジのh http://bit.ly/1w9a4Kb ? もっと玉くできそうだったら @kawachi まで