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Enhanced Depreca@on

Stuart Marks aka Dr Deprecator JDK Core Libraries Java PlaJorm Group, Oracle


#EnhancedDepreca@on

Enhanced Depreca@on • Concepts & History • Depreca@on work in JDK 9 • No@fica@on & warnings – compile-‐@me warnings – sta@c analysis tool – jdeprscan • Work in progress •  Future work

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Twi[er hashtag for ques@ons and comments


#EnhancedDepreca@on

Systems Development Life Cycle • Depreca@on is concerned with the final phase: Disposi@on

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source: wikipedia h[ps://en.wikipedia.org/wiki/Systems_development_life_cycle


#EnhancedDepreca@on

API Life Cycle • Different from socware product life cycle – nearing end, updates (bugfixes) ramped down – security vulnerabili@es only – end of support life • API life cycle – addi@on, depreca@on, and removal of feature rela@ve to a specifica,on – example: API X deprecated in Java SE 9, removed from Java SE 10 – dis@nct from Oracle JDK 9 reaching end of public update, end of support life

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#EnhancedDepreca@on

Depreca@on Key Concepts • Depreca@on is – no@fica@on to developers that they should migrate their code away from the deprecated API

• Possible reasons – the deprecated API has something wrong with it – there’s a newer, be[er API that can be used instead – the deprecated API is going to be removed

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#EnhancedDepreca@on

History (1) • Depreca@on introduced in JDK 1.1 as a javadoc tag @deprecated •  Early on, massive wave of depreca@ons for widely varying reasons – dangerous APIs (Thread.destroy) – simple renames (AWT Component.show/hide => setVisible) – caused disrup@on, compiler warnings, fear, confusion – result: depreca@ons slowed dras@cally, no APIs removed

• Annota@on @Deprecated introduced in Java 5 – note capitaliza@on – no change/clarifica@on of seman@cs

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#EnhancedDepreca@on

History (2) • Has anything ever been un-‐deprecated? – Yes! The System.getenv() API was in JDK 1.0 – first sentence of its javadoc: “Obsolete.” – implementa@on: threw an excep@on uncondi@onally – officially deprecated in 1.1 (when depreca@on was created) – fully implemented and un-‐deprecated in Java SE 5

• Has anything been newly introduced as deprecated? – Yes! Three overloads of javax.management.MBeanServer.deserialize() – introduced in Java SE 5, deprecated in Java SE 5! – JMX was a standalone JSR, with deprecated stuff, before integra@on into SE 5

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#EnhancedDepreca@on

History (3) • Confusion con@nued through Java 8 – “Don’t use deprecated APIs, since they might be removed” – “Sun/Oracle have never removed anything, and they never will”

• Wrong! We will actually remove stuff in Java 9 – [email protected]/removePropertyChangeListener – [email protected]/Unpacker.add/removePropertyChangeListener – main driver was modularity, to break dependencies on Java Beans, part of the java.desktop module – also: java.awt.Component.getPeer() removed •  flawed API, referred to types outside of Java SE, e.g., ComponentPeer

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#EnhancedDepreca@on

Depreca@on Work in Java 9 • Major clarifica@on of seman@cs •  Enhancements to @Deprecated annota@on – since=<string> – forRemoval=<boolean> – example:

@Deprecated(since="9", forRemoval=true)

•  Sta@c analysis tool: jdeprscan • Minor adjustments to JLS, javac, javadoc

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#EnhancedDepreca@on

New Depreca@on Elements •  forRemoval=<boolean> – forRemoval=true •  depreca@on is a warning that the API is subject to removal in a future spec release •  called a “terminal depreca@on” •  for Java SE, intent is that removal will occur in the next release

– forRemoval=false • merely a recommenda@on to migrate away from this API; no current intent to remove •  called an “ordinary depreca@on” •  pre-‐exis@ng depreca@ons are equivalent to forRemoval=false (the default)

•  since=<string> – the version when the API was deprecated; mostly informa@onal

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#EnhancedDepreca@on

What Happened to CONDEMNED? • Previous proposals had a reason code (enum) – SUPERSEDED, OBSOLETE, DANGEROUS, CONDEMNED, etc. – reason is a useful concept, in prac@ce hard to assign for any par@cular depreca@on – CONDEMNED is now forRemoval=true – "condemned" is easily misinterpreted, tended to generate unproduc@ve discussions

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#EnhancedDepreca@on

Java 9 Depreca@ons So Far: forRemoval=false • Boxed primi@ve constructors: new Integer(), new Boolean(), etc. – use Integer.valueOf(), Boolean.valueOf(), etc. •  java.applet – applets and browser plugins are (slowly) on their way out •  [email protected]/Observable – anybody ever use these?

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#EnhancedDepreca@on

Java 9 Depreca@ons So Far: forRemoval=true •  Thread.destroy() •  Thread.stop(Throwable) – no-‐arg Thread.stop() s@ll deprecated, but not for removal

•  System.runFinalizersOnExit(boolean) – JDK-‐4240589: if called with true, can cause unavoidable VM crash – Filed in 1999! The only fix is to remove it.

• Obsolete SecurityManager calls – inCheck, getInCheck(), currentClassLoader(), currentLoadedClass(), classDepth(), classLoaderDepth(), inClass(), inClassLoader(), checkTopLevelWindow(), ... – all ves@ges of the old security model, superseded in Java 1.2

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#EnhancedDepreca@on

No@fica@ons and Warnings • Purpose of no@fica@ons is to facilitate code migra@on • When an API is deprecated, developers need no@fica@on – code using obsolete API might have problems – the API might eventually go away, breaking code that uses it

• Goal: get depreca@on/removal informa@on to developers – avoid unpleasant surprises at compile @me – avoid unpleasant surprises at run @me

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#EnhancedDepreca@on

Kinds of No@fica@on • Compile @me – mostly compiler warnings – various severity – warnings management and suppression

•  Sta@c analysis – useful for binaries that aren’t recompiled regularly – especially 3rd party dependent libraries • Dynamic analysis – detect usage at run@me – (not part of Java 9)

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#EnhancedDepreca@on

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$ javac src/example/Deprecations.java Note: src/example/Deprecations.java uses or overrides a deprecated API. Note: Recompile with -‐Xlint:deprecation for details. $ javac -‐Xlint:deprecation src/example/Deprecations.java src/example/Deprecations.java:12: warning: [deprecation] getSelectedValues() in JList has been deprecated Object[] values = jlist.getSelectedValues(); ^ 1 warning

Compile-‐Time Warnings


#EnhancedDepreca@on

Compile-‐Time Warnings: Problem • Compile-‐@me warnings only help if you recompile – in many cases, people don’t recompile with each release – we support binary compa@bility, acer all

• Problem is worse with third party libraries – consider binary ar@facts distributed widely, e.g., from maven central – for maximum compa@bility, ocen compiled for earliest JDK release supported – many people reuse such binaries on later JDK releases

•  Your dependent libraries might use deprecated APIs – how can you tell?

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#EnhancedDepreca@on

Compile-‐Time Warnings: Problem Consider scenario: MyApp uses class SomeOldJdkClass, reuse binary

1.  Use of SomeOldJdkClass introduced è MyApp compiles fine, without warnings

2.  Next Java release: SomeOldJdkClass deprecated è MyApp con@nues to run, without warnings

3.  Next Java release: SomeOldJdkClass deprecated for removal è MyApp con@nues to run, without warnings

4.  Next Java release: SomeOldJdkClass is removed è MyApp suddenly fails at run@me with NoClassDefFoundError!

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#EnhancedDepreca@on

Solu@on: Sta@c Analysis (jdeprscan) • New tool introduced in Java 9 •  Sta@cally analyzes class files and jar files against Java SE APIs •  Looks for and reports usage of deprecated Java SE APIs

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#EnhancedDepreca@on

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public class Deprecations { void method(JList jlist) { Object[] values = jlist.getSelectedValues(); // deprecated in 7 SecurityManager sm = new RMISecurityManager(); // deprecated in 8 Boolean b2 = new Boolean(true); // deprecated in 9 } }

Solu@on: Sta@c Analysis (jdeprscan)


#EnhancedDepreca@on

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$ javac -‐version javac 1.6.0_65 $ javac -‐d classes src/example/Deprecations.java (no warnings) $ jdeprscan -‐-‐full-‐version 9-‐ea+134 $ jdeprscan -‐-‐class-‐path classes example.Deprecations class example/Deprecations uses type java/rmi/RMISecurityManager deprecated class example/Deprecations uses method javax/swing/JList getSelectedValues ()[Ljava/lang/Object; deprecated class example/Deprecations uses method in type java/rmi/RMISecurityManager deprecated class example/Deprecations uses method java/lang/Boolean <init> (Z)V deprecated

Solu@on: Sta@c Analysis (jdeprscan)


#EnhancedDepreca@on

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$ jdeprscan -‐-‐class-‐path classes -‐-‐release 9 example.Deprecations class example/Deprecations uses type java/rmi/RMISecurityManager deprecated class example/Deprecations uses method javax/swing/JList getSelectedValues ()[Ljava/lang/Object; deprecated class example/Deprecations uses method in type java/rmi/RMISecurityManager deprecated class example/Deprecations uses method java/lang/Boolean <init> (Z)V deprecated $ jdeprscan -‐-‐class-‐path classes -‐-‐release 8 example.Deprecations class example/Deprecations uses type java/rmi/RMISecurityManager deprecated class example/Deprecations uses method javax/swing/JList getSelectedValues ()[Ljava/lang/Object; deprecated class example/Deprecations uses method in type java/rmi/RMISecurityManager deprecated

jdeprscan Analysis Can Be Version-‐specific


#EnhancedDepreca@on

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$ jdeprscan -‐-‐class-‐path classes -‐-‐release 8 example.Deprecations class example/Deprecations uses type java/rmi/RMISecurityManager deprecated class example/Deprecations uses method javax/swing/JList getSelectedValues ()[Ljava/lang/Object; deprecated class example/Deprecations uses method in type java/rmi/RMISecurityManager deprecated $ jdeprscan -‐-‐class-‐path classes -‐-‐release 7 example.Deprecations class example/Deprecations uses method javax/swing/JList getSelectedValues ()[Ljava/lang/Object; deprecated $ jdeprscan -‐-‐class-‐path classes -‐-‐release 6 example.Deprecations (no output)

jdeprscan Analysis Can Be Version-‐specific

API informa,on for past releases is built into Java 9. No need to keep old versions of the JDK around.


#EnhancedDepreca@on

Terminal Depreca@on Warnings (forRemoval=true) • New state transi@on – from @Deprecated(forRemoval=false) to @Deprecated(forRemoval=true) – need an extra level of warning for this • Warnings can be suppressed with @SuppressWarnings("depreca@on") – currently suppresses both warnings, forRemoval false and true – leads to state transi@ons going undetected

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#EnhancedDepreca@on

Terminal Depreca@on Warnings (forRemoval=true) Consider scenario: MyApp uses class SomeOldJdkClass, compile each release 1.  Use of SomeOldJdkClass introduced

è MyApp compiles fine, without warnings 2.  Next Java release: SomeOldJdkClass deprecated

è MyApp compiles with warnings; @SuppressWarnings added 3.  Next Java release: SomeOldJdkClass deprecated for removal

è MyApp compiles fine, without warnings; warning s@ll suppressed 4.  Next Java release: SomeOldJdkClass is removed

è MyApp compila@on suddenly fails with error: cannot find symbol!

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#EnhancedDepreca@on

Terminal Depreca@on Warnings: Solu@on • Add new lint warning category “removal” dis@nct from “depreca@on” – @SuppressWarnings("depreca@on") •  this suppresses only ordinary depreca@on warnings, not terminal depreca@on warnings

– @SuppressWarnings("removal") •  this suppresses only terminal depreca@on warnings, not ordinary depreca@on warnings

– @SuppressWarnings({"depreca@on", "removal"}) •  if for some reason you want to suppress both kinds

– javac op@on –Xlint:removal is enabled by default •  terminal depreca@on warnings are shown without having to add op@ons •  no change to –Xlint:depreca@on

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#EnhancedDepreca@on

Legacy @deprecated Javadoc Tag Behavior • Originally, the javadoc tag was the only way to deprecate something – now, the annota@on is the preferred way – preferably, both should be present – things s@ll work if the javadoc tag is present without the annota@on

/** * My method. * @deprecated This method is obsolete. Use a newer method instead. */ @Deprecated void doSomething() { ... }

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#EnhancedDepreca@on

Legacy @deprecated Javadoc Tag Behavior • Annota@on vs. class file a[ribute – the @deprecated javadoc tag causes javac to emit a class file that contains the “Deprecated” class file a[ribute (see JVMS 4.7.15) – the @Deprecated annota@on is stored in the class file as an annota@on – they are dis@nct! – when reading a class file, javac honors both •  Time to re@re the “Deprecated” class file a[ribute? – it probably should first be... deprecated... – JDK 9: a javadoc tag without the annota@on generates a warning by default – future: the “Deprecated” class file a[ribute will no longer be generated or honored

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#EnhancedDepreca@on

Future Depreca@on Work • Develop run@me analyzer – sta@c analysis currently misses reflec@ve access to deprecated APIs

• More APIs to be deprecated – Vector, Hashtable, Enumera@on (legacy collec@ons) – [email protected] (error-‐prone, encourages poor style) – Timer, TimerTask (superseded by ScheduledThreadPoolExecutor) – Date, Calendar (superseded by java.@me) – java.corba module?

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#EnhancedDepreca@on

Future Depreca@on Work • Be[er warnings management – problem with depreca@ng oc-‐used APIs (Vector, Hashtable, Date, Calendar) – doing this generates lots of warnings – li[ering a code base with @SuppressWarnings is untenable – modifying all old usages is untenable – need be[er way of suppressing warnings – ??? maybe suppress depreca@on warnings only for specific APIs ???

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#EnhancedDepreca@on

Conclusions •  JEP 277 nearly completed – major seman@c updates and clarifica@ons – new forRemoval annota@on element (terminal depreca@on) – we’re (slowly) cleaning up the JDK! • Depreca@on life cycle requires improved no@fica@on – run the sta@c analysis tool jdeprscan – @SuppressWarnings("removal") for terminal depreca@ons

•  Links – JEP 277: h[p://openjdk.java.net/jeps/277 – JDK 9 builds: h[ps://jdk9.java.net

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Twi[er: @DrDeprecator @StuartMarks


#EnhancedDepreca@on

Safe Harbor Statement The preceding is intended to outline our general product direc@on. It is intended for informa@on purposes only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code, or func@onality, and should not be relied upon in making purchasing decisions. The development, release, and @ming of any features or func@onality described for Oracle’s products remains at the sole discre@on of Oracle.

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Documents

Enhanced*Deprecaon* - WordPress.com · – “Don’tuse*deprecated*APIs,*since*they*mightbe*removed”* – “Sun/Oracle*have*never*removed ... – consider*binary*ar@facts*distributed*widely

EnhancedDeprecaon - WordPress.com · – “Don’tusedeprecatedAPIs,sincetheymightberemoved”* – “Sun/Oraclehaveneverremoved ... – considerbinaryar@factsdistributed*widely