8 JDT embraces Type Annotations JDT embraces Type Annotations Java - PowerPoint PPT Presentation

8 8 JDT embraces Type Annotations JDT embraces Type Annotations Java 8 ready Stephan Herrmann GK Software

8 Eclipse and Java ™ 8 ● Java 8 features supported: – JSR308 - Type Annotations. – JEP120 - Repeating Annotations. – JEP118 - Method Parameter Refmection. – JSR269 - Pluggable Annotation Processor API & javax.lang.model API enhancements for Java 8. – JSR 335 – Lambda Expressions ● Lambda expressions & method/constructor references ● Support for “code carrying” interface methods ● Enhanced target typing / new overload resolution & type inference Stephan Herrmann: JDT Embraces Type Annotations - EclipseCon North America 2014 # 2

8 λ (JSR 335) Stephan Herrmann: JDT Embraces Type Annotations - EclipseCon North America 2014 # 3

8 λ Tomorrow 17:00 to 18:00: (JSR 335) Grand Peninsula C JDT embraces lambda expressions ● Srikanth [IBM India] ● Noopur Gupta [IBM India] ● Stephan Herrmann Stephan Herrmann: JDT Embraces Type Annotations - EclipseCon North America 2014 # 4

8 @ (JSR 308) Stephan Herrmann: JDT Embraces Type Annotations - EclipseCon North America 2014 # 5

8 Annotations in more Places ● Java 5: annotate declarations – ElementType: packages, classes, fjelds, methods, locals … ● Java 8: annotate types – ElementType.TYPE_USE – ElementType.TYPE_PARAMETER So what? So what? Stephan Herrmann: JDT Embraces Type Annotations - EclipseCon North America 2014 # 6

8 Why Care About Types? ● Dynamically typed languages dog1 = new Dog(); – anything goes dog1.bark(); dog2 = new Object(); – but may fail at runtime dog2.bark(); – e.g.: “method not understood” ● Type = Constraints on values To statically detect anomalies – missing capability – incompatible assignment – undeclared capability Stephan Herrmann: JDT Embraces Type Annotations - EclipseCon North America 2014 # 7

8 Why Care About Types? ● Dynamically typed languages dog1 = new Dog(); – anything goes Annotate source code: dog1.bark(); Annotate source code: ● make assumptions explicit ● make assumptions explicit dog2 = new Object(); – but may fail at runtime dog2.bark(); ● convince the compiler that code is safe ● convince the compiler that code is safe – e.g.: “method not understood” ● Type = Constraints on values To statically detect anomalies – missing capability – incompatible assignment – undeclared capability Stephan Herrmann: JDT Embraces Type Annotations - EclipseCon North America 2014 # 8

8 Why Care About Types? ● Constraint checking avoids errors – No Such Method / Field ● Basic statically typed OO – ClassCastException ● Generics – ??Exception ● SWTException("Invalid thread access") ● … ● NullPointerException Stephan Herrmann: JDT Embraces Type Annotations - EclipseCon North America 2014 # 9

8 Let the Type System Handle Nullity ● Ideally: Java would force explicit choice – String defjnitely a String, never null – String? either a String or null – Type system ensures: no dereferencing of null ● Nullity as a language feature? – Heavy weight, incompatible change – Language change for each new constraint? Stephan Herrmann: JDT Embraces Type Annotations - EclipseCon North America 2014 # 10

8 Pluggable Type System ● Make it easier to add new constraints – Only one new syntax for all kinds of constraints ● Make it easier to add new type checkers – Checker Framework (Michael Ernst – U of Washington) ● Examples – @NonNull – @Interned equals(== , equals) – @Immutable value cannot change (Java 5 ?) – @ReadOnly value cannot change via this reference – @UI code requires to run on the SWT UI thread Stephan Herrmann: JDT Embraces Type Annotations - EclipseCon North America 2014 # 11

8 Can't Java 5 Do All This? @Target(ElementType. PARAMETER ) @Target(ElementType. TYPE_USE ) @interface NonNull5 {} @interface NonNull8 {} void java5(@NonNull5 String arg); void java8(@NonNull8 String arg); arg is qualifjed to be non-null String is qualifjed to be non-null @Target(ElementType. METHOD ) @Target(ElementType. TYPE_USE ) @interface NonNull5 {} @interface NonNull8 {} @NonNull5 String java5(); @NonNull8 String java8(); java5 is qualifjed to be non-null String is qualifjed to be non-null ● We've been lying about the method result – but we can't lie about everything, e.g.: void letemBark(@NonNull List<Dog> dogs) { dogs.get(0).bark(); } NPE? Stephan Herrmann: JDT Embraces Type Annotations - EclipseCon North America 2014 # 12

8 Annotated Generics void good() { @NonNull List<@NonNull String> l1 = new ArrayList<>(); l1 cannot contain l1.add("Hello"); null elements for (String elem : l1) System. out .println(elem.toUpperCase()); @NonNull List<@Nullable String> l2 = new ArrayList<>(); @NonNull List<@Nullable String> l2 = new ArrayList<>(); l2 can contain l2.add( null ); null elements for (String unknown : l2) if (unknown != null ) System. out .println(unknown.toUpperCase()); } void bad(List<String> unknown, List<@Nullable String> withNulls) { @NonNull List<@NonNull String> l1 = new ArrayList<>(); l1.add( null ); String first = l1.get(0); Null type mismatch: required '@NonNull String' Null type mismatch: required '@NonNull String' if (first == null ) return ; but the provided value is null but the provided value is null l1 = unknown; l1 = withNulls; String canNull = withNulls.get(0); System. out .println(canNull.toUpperCase()); } Stephan Herrmann: JDT Embraces Type Annotations - EclipseCon North America 2014 # 13

8 Annotated Generics void good() { @NonNull List<@NonNull String> l1 = new ArrayList<>(); l1 cannot contain l1.add("Hello"); null elements for (String elem : l1) System. out .println(elem.toUpperCase()); @NonNull List<@Nullable String> l2 = new ArrayList<>(); @NonNull List<@Nullable String> l2 = new ArrayList<>(); l2 can contain l2.add( null ); null elements for (String unknown : l2) if (unknown != null ) System. out .println(unknown.toUpperCase()); } void bad(List<String> unknown, List<@Nullable String> withNulls) { @NonNull List<@NonNull String> l1 = new ArrayList<>(); l1.add( null ); String first = l1.get(0); if (first == null ) return ; Null comparison always yields false: Null comparison always yields false: l1 = unknown; The variable fjrst cannot be null at this location The variable fjrst cannot be null at this location l1 = withNulls; String canNull = withNulls.get(0); System. out .println(canNull.toUpperCase()); } Stephan Herrmann: JDT Embraces Type Annotations - EclipseCon North America 2014 # 14

8 Annotated Generics void good() { @NonNull List<@NonNull String> l1 = new ArrayList<>(); l1 cannot contain l1.add("Hello"); null elements for (String elem : l1) System. out .println(elem.toUpperCase()); @NonNull List<@Nullable String> l2 = new ArrayList<>(); @NonNull List<@Nullable String> l2 = new ArrayList<>(); l2 can contain l2.add( null ); null elements for (String unknown : l2) if (unknown != null ) System. out .println(unknown.toUpperCase()); } void bad(List<String> unknown, List<@Nullable String> withNulls) { @NonNull List<@NonNull String> l1 = new ArrayList<>(); l1.add( null ); String first = l1.get(0); if (first == null ) return ; l1 = unknown; l1 = withNulls; Null type safety (type annotations): The expression of type 'List<String>' Null type safety (type annotations): The expression of type 'List<String>' needs unchecked conversion to conform to '@NonNull List<@NonNull String>' needs unchecked conversion to conform to '@NonNull List<@NonNull String>' String canNull = withNulls.get(0); System. out .println(canNull.toUpperCase()); } Stephan Herrmann: JDT Embraces Type Annotations - EclipseCon North America 2014 # 15

8 Annotated Generics void good() { @NonNull List<@NonNull String> l1 = new ArrayList<>(); l1 cannot contain l1.add("Hello"); null elements for (String elem : l1) System. out .println(elem.toUpperCase()); @NonNull List<@Nullable String> l2 = new ArrayList<>(); @NonNull List<@Nullable String> l2 = new ArrayList<>(); l2 can contain l2.add( null ); null elements for (String unknown : l2) if (unknown != null ) System. out .println(unknown.toUpperCase()); } void bad(List<String> unknown, List<@Nullable String> withNulls) { @NonNull List<@NonNull String> l1 = new ArrayList<>(); l1.add( null ); String first = l1.get(0); if (first == null ) return ; l1 = unknown; l1 = withNulls; Null type mismatch (type annotations): Null type mismatch (type annotations): String canNull = withNulls.get(0); required '@NonNull List<@NonNull String>' required '@NonNull List<@NonNull String>' System. out .println(canNull.toUpperCase()); but this expression has type 'List<@Nullable String>' } but this expression has type 'List<@Nullable String>' Stephan Herrmann: JDT Embraces Type Annotations - EclipseCon North America 2014 # 16