JVM Internals - NEJUG Nov 2010

1. JVM Internals Douglas Q. Hawkins - dougqh@gmail.com http://www.dougqh.net/ Wednesday, November 10, 2010

2. JVM Internals Douglas Q. Hawkins - dougqh@gmail.com http://www.dougqh.net/ http://www.meetup.com/boston-java Wednesday, November 10, 2010

3. JVM Internals HotSpot Garbage Collector HotSpot Optimizations Class File Format & Byte Code Compile Time Run Time Demos Presentation Materials http://www.slideshare.net/dougqh https://github.com/dougqh Wednesday, November 10, 2010

4. Garbage Collection Wednesday, November 10, 2010

5. Garbage Collection Current HotSpot Collectors Demos Garbage First (G1) Collector Wednesday, November 10, 2010

6. Generational Hypothesis Generational Hypothesis 92 to 98% objects die young Few references exist from old objects to new objects http://www.devx.com/Java/Article/21977 http://www.ibm.com/developerworks/java/library/j-jtp09275.html http://java.sun.com/j2se/reference/whitepapers/memorymanagement_whitepaper.pdf Wednesday, November 10, 2010

7. HotSpot Garbage Collector Heap http://download.oracle.com/javase/1.5.0/docs/guide/vm/gc-ergonomics.html http://java.sun.com/j2se/reference/whitepapers/memorymanagement_whitepaper.pdf Wednesday, November 10, 2010

8. HotSpot Garbage Collector Young Generation Old Generation http://download.oracle.com/javase/1.5.0/docs/guide/vm/gc-ergonomics.html http://java.sun.com/j2se/reference/whitepapers/memorymanagement_whitepaper.pdf Wednesday, November 10, 2010

9. HotSpot Garbage Collector Young Generation Eden S1 S2 Old Generation http://download.oracle.com/javase/1.5.0/docs/guide/vm/gc-ergonomics.html http://java.sun.com/j2se/reference/whitepapers/memorymanagement_whitepaper.pdf Wednesday, November 10, 2010

10. Object Allocation Young Generation Eden S1 S2 Old Generation http://blogs.sun.com/jonthecollector/entry/the_real_thing http://blogs.sun.com/jonthecollector/entry/a_little_thread_privacy_please Wednesday, November 10, 2010

18. Object Allocation TLAB Young Generation Eden S1 S2 Old Generation http://blogs.sun.com/jonthecollector/entry/the_real_thing http://blogs.sun.com/jonthecollector/entry/a_little_thread_privacy_please Wednesday, November 10, 2010

27. Minor Collection TLAB Young Generation Eden S1 S2 Old Generation http://www.fasterj.com/articles/G1.shtml http://java.sun.com/docs/hotspot/gc1.4.2/faq.html http://www.oracle.com/technetwork/java/gc-tuning-5-138395.html Wednesday, November 10, 2010

30. Minor Collection Young Generation Eden S1 S2 Old Generation http://www.fasterj.com/articles/G1.shtml http://java.sun.com/docs/hotspot/gc1.4.2/faq.html http://www.oracle.com/technetwork/java/gc-tuning-5-138395.html Wednesday, November 10, 2010

38. Application Thread GC Thread http://www.austinjug.org/presentations/JDK6PerfUpdate_Dec2009.pdf Wednesday, November 10, 2010

39. Stop the World! Application Thread GC Thread http://www.austinjug.org/presentations/JDK6PerfUpdate_Dec2009.pdf Wednesday, November 10, 2010

40. Application Thread GC Thread http://www.austinjug.org/presentations/JDK6PerfUpdate_Dec2009.pdf Wednesday, November 10, 2010

41. Serial Application Thread GC Thread http://www.austinjug.org/presentations/JDK6PerfUpdate_Dec2009.pdf Wednesday, November 10, 2010

42. Serial Parallel Application Thread GC Thread http://www.austinjug.org/presentations/JDK6PerfUpdate_Dec2009.pdf Wednesday, November 10, 2010

43. Demo Wednesday, November 10, 2010

44. Major Collection Young Generation Eden S1 S2 Old Generation http://www.devx.com/Java/Article/21977/0 http://www.austinjug.org/presentations/JDK6PerfUpdate_Dec2009.pdf http://java.sun.com/j2se/reference/whitepapers/memorymanagement_whitepaper.pdf Wednesday, November 10, 2010

55. Serial Mark Parallel Mark Sweep & Compact Sweep & Compact Application Thread GC Thread http://www.devx.com/Java/Article/21977/0/page/3 http://www.austinjug.org/presentations/JDK6PerfUpdate_Dec2009.pdf Wednesday, November 10, 2010

56. Serial Mark Parallel Mark Sweep & Compact Sweep & Compact Application Thread GC Thread http://www.devx.com/Java/Article/21977/0/page/3 http://www.austinjug.org/presentations/JDK6PerfUpdate_Dec2009.pdf Wednesday, November 10, 2010

57. Serial Mark Parallel Mark Sweep & Compact Sweep & Compact Concurrent Mark & Sweep Application Thread GC Thread http://www.devx.com/Java/Article/21977/0/page/3 http://www.austinjug.org/presentations/JDK6PerfUpdate_Dec2009.pdf Wednesday, November 10, 2010

58. Serial Mark Parallel Mark Sweep & Compact Sweep & Compact Concurrent Mark & Sweep Concurrent Marking Remark Concurrent Sweep Application Thread GC Thread http://www.devx.com/Java/Article/21977/0/page/3 http://www.austinjug.org/presentations/JDK6PerfUpdate_Dec2009.pdf Wednesday, November 10, 2010

60. Permanent Generation Young Generation Eden S1 S2 Old Generation http://opensource.atlassian.com/conﬂuence/spring/pages/viewpage.action?pageId=2669 http://dow.ngra.de/2009/06/15/classloaderlocal-how-to-avoid-classloader-leaks-on-application-redeploy/ Wednesday, November 10, 2010

61. Permanent Generation Young Generation Eden S1 S2 Old Generation Permanent Generation http://opensource.atlassian.com/conﬂuence/spring/pages/viewpage.action?pageId=2669 http://dow.ngra.de/2009/06/15/classloaderlocal-how-to-avoid-classloader-leaks-on-application-redeploy/ Wednesday, November 10, 2010

62. Permanent Generation Young Generation Eden S1 S2 Old Generation Permanent Generation Bootstrap App Server Web Application http://opensource.atlassian.com/conﬂuence/spring/pages/viewpage.action?pageId=2669 http://dow.ngra.de/2009/06/15/classloaderlocal-how-to-avoid-classloader-leaks-on-application-redeploy/ Wednesday, November 10, 2010

66. Permanent Generation Young Generation Eden S1 S2 Old Generation Permanent Generation Bootstrap App Server http://opensource.atlassian.com/conﬂuence/spring/pages/viewpage.action?pageId=2669 http://dow.ngra.de/2009/06/15/classloaderlocal-how-to-avoid-classloader-leaks-on-application-redeploy/ Wednesday, November 10, 2010

68. Java 6 Collectors Parallel Parallel Young Serial New Scavenge Serial Old Concurrent Parallel Old (Mark Sweep Mark & Old Compact) Sweep http://www.petefreitag.com/articles/gctuning/ http://blogs.sun.com/jonthecollector/entry/our_collectors http://openjdk.java.net/groups/hotspot/docs/HotSpotGlossary.html Wednesday, November 10, 2010

69. Java 6 Collectors -XX:+UseSerialGC Parallel Parallel Young Serial New Scavenge Serial Old Concurrent Parallel Old (Mark Sweep Mark & Old Compact) Sweep http://www.petefreitag.com/articles/gctuning/ http://blogs.sun.com/jonthecollector/entry/our_collectors http://openjdk.java.net/groups/hotspot/docs/HotSpotGlossary.html Wednesday, November 10, 2010

70. Java 6 Collectors -XX:+UseParNewGC Parallel Parallel Young Serial New Scavenge Serial Old Concurrent Parallel Old (Mark Sweep Mark & Old Compact) Sweep http://www.petefreitag.com/articles/gctuning/ http://blogs.sun.com/jonthecollector/entry/our_collectors http://openjdk.java.net/groups/hotspot/docs/HotSpotGlossary.html Wednesday, November 10, 2010

71. Java 6 Collectors -XX:+UseParallelGC Parallel Parallel Young Serial New Scavenge Serial Old Concurrent Parallel Old (Mark Sweep Mark & Old Compact) Sweep http://www.petefreitag.com/articles/gctuning/ http://blogs.sun.com/jonthecollector/entry/our_collectors http://openjdk.java.net/groups/hotspot/docs/HotSpotGlossary.html Wednesday, November 10, 2010

72. Java 6 Collectors -XX:+UseConcMarkSweepGC Parallel Parallel Young Serial New Scavenge Serial Old Concurrent Parallel Old (Mark Sweep Mark & Old Compact) Sweep http://www.petefreitag.com/articles/gctuning/ http://blogs.sun.com/jonthecollector/entry/our_collectors http://openjdk.java.net/groups/hotspot/docs/HotSpotGlossary.html Wednesday, November 10, 2010

73. Java 6 Collectors -XX:+UseParallelOldGC Parallel Parallel Young Serial New Scavenge Serial Old Concurrent Parallel Old (Mark Sweep Mark & Old Compact) Sweep http://www.petefreitag.com/articles/gctuning/ http://blogs.sun.com/jonthecollector/entry/our_collectors http://openjdk.java.net/groups/hotspot/docs/HotSpotGlossary.html Wednesday, November 10, 2010

74. Java 6 Collectors Parallel Parallel Young Serial New Scavenge Serial Old Concurrent Parallel Old (Mark Sweep Mark & Old Compact) Sweep http://www.petefreitag.com/articles/gctuning/ http://blogs.sun.com/jonthecollector/entry/our_collectors http://openjdk.java.net/groups/hotspot/docs/HotSpotGlossary.html Wednesday, November 10, 2010

75. Java 6 Collectors Parallel Parallel Young Serial New Scavenge G1 Serial Old Concurrent Parallel Old (Mark Sweep Mark & Old Compact) Sweep http://www.petefreitag.com/articles/gctuning/ http://blogs.sun.com/jonthecollector/entry/our_collectors http://openjdk.java.net/groups/hotspot/docs/HotSpotGlossary.html Wednesday, November 10, 2010

76. G1 - Garbage First Heap http://developers.sun.com/learning/javaoneonline/2008/pdf/TS-5419.pdf Wednesday, November 10, 2010

77. G1 - Garbage First http://developers.sun.com/learning/javaoneonline/2008/pdf/TS-5419.pdf Wednesday, November 10, 2010

78. G1 - Garbage First Unused http://developers.sun.com/learning/javaoneonline/2008/pdf/TS-5419.pdf Wednesday, November 10, 2010

79. G1 - Garbage First Unused Young http://developers.sun.com/learning/javaoneonline/2008/pdf/TS-5419.pdf Wednesday, November 10, 2010

80. G1 - Garbage First Unused Young Old http://developers.sun.com/learning/javaoneonline/2008/pdf/TS-5419.pdf Wednesday, November 10, 2010

81. G1 - Minor Collection Unused Young Old Wednesday, November 10, 2010

90. G1 - Major Collection Unused Young Old Wednesday, November 10, 2010

99. Break Wednesday, November 10, 2010

100. HotSpot Optimizations Wednesday, November 10, 2010

101. HotSpot Optimizations Compiler Optimizations Runtime Optimizations Wednesday, November 10, 2010

102. Class File Format & Byte Code Wednesday, November 10, 2010

103. Class File Format & Byte Code Class File Layout & Parts Introduction to Byte Code Examples of Java Compiled to Byte Code Wednesday, November 10, 2010

104. Class File Format CA FE BA BE Minor Version Major Version Constant Pool Flags This Class Super Class Interfaces Fields Methods Attributes http://java.sun.com/docs/books/jvms/second_edition/ClassFileFormat-Java5.pdf Wednesday, November 10, 2010

108. Class File Format CA FE BA BE Minor Version Major Version Constant Pool n Flags This Class Super Class pu te d tio ce iva te er ct ta ab tfp pr ec int ra fa ic um pr ic no Interfaces st bl ric ot al at en an ﬁn st st Fields Methods Attributes http://java.sun.com/docs/books/jvms/second_edition/ClassFileFormat-Java5.pdf Wednesday, November 10, 2010

115. Field Format Flags Name Descriptor Attributes Wednesday, November 10, 2010

116. Field Format Flags Name Descriptor pu te d lat nt iva te ile vo ie pr ec ic pr ic ns Attributes bl ot al at tra ﬁn Wednesday, November 10, 2010 st

117. Field Format Flags Name Descriptor “name” Attributes Wednesday, November 10, 2010

118. Field Format Flags Name Descriptor “Ljava/lang/String;” Attributes Wednesday, November 10, 2010

119. Field Format Flags Name Descriptor Attributes Wednesday, November 10, 2010

120. Field Format Flags Name Descriptor Attributes ConstantValue Wednesday, November 10, 2010

121. Method Format Flags Name Descriptor Attributes Wednesday, November 10, 2010

122. Wednesday, November 10, 2010 Name Flags st Method Format ric tfp Attributes na tiv va e ra rg s Descriptor sy nc ﬁn hr al on st ize at d pr ic ot pr ec iva te pu te d bl ic

123. Method Format Flags Name Descriptor “main” Attributes Wednesday, November 10, 2010

124. Method Format Flags Name Descriptor “([Ljava/lang/String;)V” Attributes Wednesday, November 10, 2010

125. Method Format Flags Name Descriptor Attributes Wednesday, November 10, 2010

126. Method Format Flags Name Descriptor Attributes Exceptions Wednesday, November 10, 2010

127. Method Format Flags Name Descriptor Attributes Exceptions Code Wednesday, November 10, 2010

128. Browsing Class File Format JClassLib Viewer http://www.ej-technologies.com/products/jclasslib/overview.html JAD http://www.varaneckas.com/jad Wednesday, November 10, 2010

129. Byte Code Wednesday, November 10, 2010

130. Stack Based Virtual Machine 0 iconst_1 0 1 2 3 1 iconst_2 2 iadd 3 istore_0 4 iload_0 Wednesday, November 10, 2010

131. Stack Based Virtual Machine 0 iconst_1 0 1 2 3 1 iconst_2 2 iadd 3 istore_0 4 iload_0 1 Wednesday, November 10, 2010

132. Stack Based Virtual Machine 0 iconst_1 0 1 2 3 1 iconst_2 2 iadd 3 istore_0 4 iload_0 2 1 Wednesday, November 10, 2010

133. Stack Based Virtual Machine 0 iconst_1 0 1 2 3 1 iconst_2 2 iadd 3 istore_0 4 iload_0 1+2 Wednesday, November 10, 2010

134. Stack Based Virtual Machine 0 iconst_1 0 1 2 3 1 iconst_2 2 iadd 3 istore_0 4 iload_0 3 Wednesday, November 10, 2010

135. Stack Based Virtual Machine 0 iconst_1 0 1 2 3 1 iconst_2 3 2 iadd 3 istore_0 4 iload_0 Wednesday, November 10, 2010

136. Stack Based Virtual Machine 0 iconst_1 0 1 2 3 1 iconst_2 3 2 iadd 3 istore_0 4 iload_0 3 Wednesday, November 10, 2010

138. Operation Types Load and Store Arithmetic and Logic Type Conversion Control Transfer Object Creation and Manipulation Operand Stack Method Invocation Wednesday, November 10, 2010

139. Data Types x reﬁ als ns de P ray Loc ac ts By ture St tan Co k/ na te Sig Co Ar boolean Z Integer Types byte B b char C c short S s int I i long J l ﬂoat F f double D d reference L a void V Wednesday, November 10, 2010

140. Parameters and Local Variables static int volume( int width, int depth, int height ) { int area = width * depth; int volume = area * height; return volume; } Wednesday, November 10, 2010

141. Parameters and Local Variables static int volume( 0 iload_0 int width, 1 iload_1 int depth, int height ) 2 imul { 3 istore_3 int area = width * depth; 4 iload_3 int volume = area * height; return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 11ireturn Wednesday, November 10, 2010

142. Parameters and Local Variables static int volume( 0 iload_0 int width, 1 iload_1 int depth, int height ) 2 imul e t h lum igh h pt a dt { are 3 istore_3 de he wi vo 0 1 2 3 4 int area = width * depth; 4 iload_3 int volume = area * height; return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 11ireturn Wednesday, November 10, 2010

143. Parameters and Local Variables static int volume( 0 iload_0 int width, 1 iload_1 int depth, int height ) 2 imul e t h lum igh h pt a dt { are 3 istore_3 de he wi vo 0 1 2 3 4 int area = width * depth; int volume = area * height; 4 iload_3 1 2 3 return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 11ireturn Wednesday, November 10, 2010

144. Parameters and Local Variables static int volume( 0 iload_0 int width, 1 iload_1 int depth, int height ) 2 imul e t h lum igh h pt a dt { are 3 istore_3 de he wi vo 0 1 2 3 4 int area = width * depth; int volume = area * height; 4 iload_3 1 2 3 return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 11ireturn 1 Wednesday, November 10, 2010

145. Parameters and Local Variables static int volume( 0 iload_0 int width, 1 iload_1 int depth, int height ) 2 imul e t h lum igh h pt a dt { are 3 istore_3 de he wi vo 0 1 2 3 4 int area = width * depth; int volume = area * height; 4 iload_3 1 2 3 return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 2 11ireturn 1 Wednesday, November 10, 2010

146. Parameters and Local Variables static int volume( 0 iload_0 int width, 1 iload_1 int depth, int height ) 2 imul e t h lum igh h pt a dt { are 3 istore_3 de he wi vo 0 1 2 3 4 int area = width * depth; int volume = area * height; 4 iload_3 1 2 3 return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 11ireturn 2 Wednesday, November 10, 2010

147. Parameters and Local Variables static int volume( 0 iload_0 int width, 1 iload_1 int depth, int height ) 2 imul e t h lum igh h pt a dt { are 3 istore_3 de he wi vo 0 1 2 3 4 int area = width * depth; int volume = area * height; 4 iload_3 1 2 3 2 return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 11ireturn Wednesday, November 10, 2010

148. Parameters and Local Variables static int volume( 0 iload_0 int width, 1 iload_1 int depth, int height ) 2 imul e t h lum igh h pt a dt { are 3 istore_3 de he wi vo 0 1 2 3 4 int area = width * depth; int volume = area * height; 4 iload_3 1 2 3 2 return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 11ireturn 2 Wednesday, November 10, 2010

149. Parameters and Local Variables static int volume( 0 iload_0 int width, 1 iload_1 int depth, int height ) 2 imul e t h lum igh h pt a dt { are 3 istore_3 de he wi vo 0 1 2 3 4 int area = width * depth; int volume = area * height; 4 iload_3 1 2 3 2 return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 3 11ireturn 2 Wednesday, November 10, 2010

150. Parameters and Local Variables static int volume( 0 iload_0 int width, 1 iload_1 int depth, int height ) 2 imul e t h lum igh h pt a dt { are 3 istore_3 de he wi vo 0 1 2 3 4 int area = width * depth; int volume = area * height; 4 iload_3 1 2 3 2 return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 11ireturn 6 Wednesday, November 10, 2010

151. Parameters and Local Variables static int volume( 0 iload_0 int width, 1 iload_1 int depth, int height ) 2 imul e t h lum igh h pt a dt { are 3 istore_3 de he wi vo 0 1 2 3 4 int area = width * depth; int volume = area * height; 4 iload_3 1 2 3 2 6 return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 11ireturn Wednesday, November 10, 2010

152. Parameters and Local Variables static int volume( 0 iload_0 int width, 1 iload_1 int depth, int height ) 2 imul e t h lum igh h pt a dt { are 3 istore_3 de he wi vo 0 1 2 3 4 int area = width * depth; int volume = area * height; 4 iload_3 1 2 3 2 6 return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 11ireturn 6 Wednesday, November 10, 2010

153. Parameters and Local Variables static int volume( 0 iload_0 int width, 1 iload_1 int depth, int height ) 2 imul e t h lum igh h pt a dt { are 3 istore_3 de he wi vo 0 1 2 3 4 int area = width * depth; int volume = area * height; 4 iload_3 1 2 3 2 6 return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 11ireturn Wednesday, November 10, 2010

154. Static vs Virtual Methods static int volume( 0 iload_0 int width, 1 iload_1 int depth, 2 imul e int height ) are t h lum h igh pt a dt { 3 istore_3 de he wi vo 0 1 2 3 4 5 int area = width * depth; 4 iload_3 int volume = area * height; return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 11 ireturn Wednesday, November 10, 2010

155. Static vs Virtual Methods int volume( 0 iload_0 int width, 1 iload_1 int depth, 2 imul e int height ) are t h lum h igh pt a dt { 3 istore_3 de he wi vo 0 1 2 3 4 5 int area = width * depth; 4 iload_3 int volume = area * height; return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 11 ireturn Wednesday, November 10, 2010

156. Static vs Virtual Methods int volume( 0 iload_0 int width, 1 iload_1 int depth, 2 imul e int height ) are t he h lum h igh pt a dt s { 3 istore_3 de thi wi vo 0 1 2 3 4 5 int area = width * depth; 4 iload_3 int volume = area * height; return volume; 5 iload_2 } 6 imul 7 istore 4 9 iload 4 11 ireturn Wednesday, November 10, 2010

157. Static vs Virtual Methods int volume( 0 iload_1 int width, 1 iload_2 int depth, 2 imul e int height ) are t he h lum h igh pt a dt s { 3 istore 4 de thi wi vo 0 1 2 3 4 5 int area = width * depth; 5 iload 4 int volume = area * height; return volume; 7 iload_3 } 8 imul 9 istore 5 11 iload 5 13 ireturn Wednesday, November 10, 2010

158. Hello World System.out.println( “Hello World” ); Wednesday, November 10, 2010

159. Hello World System.out.println( “Hello World” ); 0 getstatic System.out 3 ldc “Hello World” 5 invokevirtual PrintStream.println 8 return Wednesday, November 10, 2010

160. Hello World System.out.println( “Hello World” ); 0 1 2 3 0 getstatic System.out 3 ldc “Hello World” 5 invokevirtual PrintStream.println “Hello World” 8 return System.out Wednesday, November 10, 2010

163. Hello World g s ms thi System.out.println( “Hello World” ); 0 1 2 3 0 getstatic System.out 3 ldc “Hello World” 5 invokevirtual PrintStream.println “Hello World” 8 return System.out Wednesday, November 10, 2010

164. Types of Method Invocations invokestatic - invoke static methods invokevirtual - invoke instance method from class invokeinterface - invoke instance method from interface invokespecial - invoke <init> / invoke super method Wednesday, November 10, 2010

165. New Object return new BigDecimal(“2.0”); Wednesday, November 10, 2010

166. New Object return new BigDecimal(“2.0”); 0 new BigDecimal 3 dup 4 ldc “2.0” 6 invokespecial BigDecimal.<init> 9 areturn Wednesday, November 10, 2010

167. New Object return new BigDecimal(“2.0”); 0 1 2 3 0 new BigDecimal 3 dup 4 ldc “2.0” “2.0” 6 invokespecial BigDecimal.<init> 9 areturn Wednesday, November 10, 2010

168. New Object return new BigDecimal(“2.0”); 0 1 2 3 0 new BigDecimal 3 dup 4 ldc “2.0” “2.0” 6 invokespecial BigDecimal.<init> 9 areturn BigDecimal Wednesday, November 10, 2010

173. If / Else static boolean isPositive( int val ){ if ( val > 0 ) { return true; } else { return false; } } Wednesday, November 10, 2010

174. If / Else static boolean isPositive( int val ){ 0 iload_0 test if ( val > 0 ) { 1 iﬂe +5 //6 return true; 4 iconst_1 } else { if return false; 5 ireturn } 6 iconst_0 else } 7 ireturn Wednesday, November 10, 2010

178. If / Else static boolean isPositive( int val ){ 0 iload_0 test if ( val > 0 ) { 1 iﬂe +5 //6 return true; 4 iconst_1 } else { if return false; 5 ireturn } 6 iconst_0 else } 7 ireturn static boolean isPositive( int val ){ return ( val > 0 ); } Wednesday, November 10, 2010

179. If / Else static boolean isPositive( int val ){ if ( val > 0 ) { return true; } else { return false; } } static boolean isPositive( int val ){ return ( val > 0 ); } Wednesday, November 10, 2010

180. If / Else static boolean isPositive( int val ){ 0 iload_0 test if ( val > 0 ) { 1 iﬂe +5 //6 return true; 4 iconst_1 } else { if return false; 5 ireturn } 6 iconst_0 else } 7 ireturn static boolean isPositive( int val ){ return ( val > 0 ); } Wednesday, November 10, 2010

181. For Loop static int sum( int min, int max ){ int sum = 0; for ( int i=min; i<max; ++i ){ sum += i; } return sum; } Wednesday, November 10, 2010

182. before 0 iconst_0 For Loop init & test loop 1 istore_2 2 iload_1 static int sum( int min, int max ){ 3 istore_3 int sum = 0; 4 goto +10 //14 for ( int i=min; i<max; ++i ){ 7 iload_2 loop body sum += i; 8 iload_3 } 9 iadd return sum; 10 istore_2 } inc 11 iinc 3 by 1 14 iload_3 test 15 iload_1 16 if_icmplt -9 //7 19 iload_2 after loop 20 ireturn Wednesday, November 10, 2010

189. Exception Handling static int read( InputStream in ) { try { return in.read(); } catch ( IOException e ) { return -1; } ﬁnally { IoUtils.closeQuietly( in ); } } Wednesday, November 10, 2010

JVM Internals - NEJUG Nov 2010

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JVM Internals - NEJUG Nov 2010