Language Features for JDK7

2. Language Features for JDK7 Neal GafterJoshua Bloch Google

3. A slate of possible small language changes • Improved type inference • Enum comparison • String switch • Chained invocations & Extension methods • Improved catch clauses • Array notation for Map, List • Typedef • Serialization annotations • Self type • Properties www.javapolis.com

4. Improved type inference: constructors • Today: Map<String, List<String>> anagrams = new HashMap<String, List<String>>(); www.javapolis.com

5. Improved type inference: constructors • Proposed: Map<String, List<String>> anagrams = new HashMap<>(); www.javapolis.com

6. Improved type inference: argument positions • Today: public <E> Set<E> emptySet() { … } void timeWaitsFor(Set<Man> people) { … } // * Won't compile! timeWaitsFor(Collections.emptySet()); www.javapolis.com

7. Improved type inference: argument positions • Today: public <E> Set<E> emptySet() { … } void timeWaitsFor(Set<Man> people) { … } // OK timeWaitsFor(Collections.<Man>emptySet()); www.javapolis.com

8. Improved type inference: argument positions • Proposed: public <E> Set<E> emptySet() { … } void timeWaitsFor(Set<Man> people) { … } // OK timeWaitsFor(Collections.emptySet()); www.javapolis.com

9. Enum comparison • Today enum Size { SMALL, MEDIUM, LARGE } if (mySize.compareTo(yourSize) >= 0) System.out.println(“You can wear my pants.”); www.javapolis.com

10. Enum comparison • Proposed enum Size { SMALL, MEDIUM, LARGE } if (mySize > yourSize) System.out.println(“You can wear my pants.”); www.javapolis.com

11. String switch • Today static boolean booleanFromString(String s) { if (s.equals("true")) { return true; } else if (s.equals("false")) { return false; } else { throw new IllegalArgumentException(s); } } www.javapolis.com

12. String switch • Proposed static boolean booleanFromString(String s) { switch(s) { case "true": return true; case "false": return false; default: throw new IllegalArgumentException(s); } } www.javapolis.com

13. Chained invocations and Extension Methods • Enables declarative style: List<String> strings = ...; strings .filter(isCountryName) // could be a closure .sort() .uniq() .each(printString); // ditto www.javapolis.com

14. Extension methods • Today import java.util.Collections; List<String> list = …; Collections.sort(list); www.javapolis.com

15. Extension methods • Proposed import static java.util.Collections.sort; List<String> list = …; list.sort(); www.javapolis.com

16. Chained invocations • Today class Builder { void setSomething(Something x) { … } void setOther(Other x) { … } Thing result() { … } } Builder builder = new Builder(); builder.setSomething(something); builder.setOther(other); Thing thing = builder.result(); www.javapolis.com

17. Chained invocations • Proposed class Builder { void setSomething(Something x) { … } void setOther(Other x) { … } Thing result() { … } } Thing thing = new Builder() .setSomething(something) .setOther(other) .result(); www.javapolis.com

18. Chained invocations and Extension Methods • Enables declarative style: List<String> strings = ...; strings .filter(isCountryName) // could be a closure .sort() .uniq() .each(printString); // ditto www.javapolis.com

19. Improved catch clauses: catching multiple types • Today: try { return klass.newInstance(); } catch (InstantiationException e) { throw new AssertionError(e); } catch (IllegalAccessException e) { throw new AssertionError(e); } www.javapolis.com

20. Improved catch clauses: catching multiple types • Proposed: try { return klass.newInstance(); } catch (InstantiationException | IllegalAccessException e) { throw new AssertionError(e); } www.javapolis.com

21. Improved catch clauses: rethrown exceptions • Today: try { doable.doit(); // Throws several types } catch (Throwable ex) { logger.log(ex); throw ex; // Error: Throwable not declared } www.javapolis.com

22. Improved catch clauses: rethrown exceptions • Proposed: try { doable.doit(); // Throws several types } catch (final Throwable ex) { logger.log(ex); throw ex; // OK: Throws the same several types } www.javapolis.com

23. Array notation for Map, List • Today: void swap(List<String> list, int i, int j) { String s1 = list.get(i); list.set(i, list.get(j)); list.set(j, s1); } www.javapolis.com

24. Array notation for Map, List • Proposed: void swap(List<String> list, int i, int j) { String s1 = list[i]; list[i] = list[j]; list[j] = s1; } www.javapolis.com

25. Array notation for Map, List • Today: Map<Input,Output> cache = …; Output cachedComputation(Input in) { Output out = cache.get(in); if (out == null) { out = computation(input); cache.put(in, out); } return out; } www.javapolis.com

26. Array notation for Map, List • Proposed: Map<Input,Output> cache = …; Output cachedComputation(Input in) { Output out = cache[in]; if (out == null) { out = computation(input); cache[in]= out; } return out; } www.javapolis.com

27. Self Type • Today class Buffer { Buffer flip() { … } Buffer position(int newPos) { … } Buffer limit(int newLimit) { … } } class ByteBuffer extends Buffer { ByteBuffer put(byte data) { … } } www.javapolis.com

28. Self Type • Today ByteBuffer buf = ...; buf.flip().position(12); // OK buf.flip().put(12); // Error www.javapolis.com

29. Self Type • Proposed class Buffer { this flip() { … } this position(int newPos) { … } this limit(int newLimit) { … } } class ByteBuffer extends Buffer { this put(byte data) { … } } www.javapolis.com

30. Typedef import java.util.Map<String,String> as MyProperties; import java.util.Map<String,T> as Lookup<T>; // if we add BGGA function types import { double => double } as DoubleFcn; Alternatively static class MyProperties = Map<String,String>; static class Lookup<T> = Map<String,T>; // if we add BGGA function types static class DoubleFcn = { double => double }; www.javapolis.com

31. Q&A View JavaPolis talks @ www.parleys.com

32. Thank you for your attention