Bart van Kuik Application Developer Oracle Corporation

Java 1.5 New Language Features

Java 1.5: Tiger  Less boilerplate code through syntax changes  But no new keywords so compatibility with existing code, except the enum keyword

Additions to Syntax  Generics  Enhanced for loop  Autoboxing/unboxing  Typesafe enums  Static Imports  Varargs  Metadata

Generics  Also called 'parameterized types', since you pass a parameter upon declaration and instantiation: List lijstMetNamen = new ArrayList (); // 1.4: runtime error / 1.5: compiler error lijstMetNamen.add(new Integer(1));  Feature: covariant return types

Enhanced for loop // Old syntax with iterators: List list = new ArrayList(); for(Iterator i = list.iterator(); i.hasNext();) { String s = (String) i.next(); System.out.println("String: " + s); } // New syntax List list = new ArrayList (); for (String s : list) { // do something} // The following is also possible: String naam = "Harry"; for (char c : naam.toCharArray()) { // do something }

Autoboxing/unboxing  public static void Cow.milk(Integer liter); public static void Monkey.throw(int distance);  From primitive to reference and back: int i = 4; Cow.milk(new Integer(i)); // 1.4 Cow.milk(i); // 1.5 Object obj = new Integer(3); Monkey.throw(((Integer)obj).intValue()); // 1.4 Monkey.throw((Integer)obj); // 1.5  Boxing null gives a NullPointerException

Typesafe enum s  Various disadvantages: class Kaart { static final int HARTEN = 0; static final int KLAVEREN = 1; static final int RUITEN = 2; static final int SCHOPPEN = 3; }  New syntax: public enum Kaart { harten, klaveren, ruiten, schoppen }

Static Imports  Before 1.5: lots of typing work to get a constant: ErrorConstants.XML_NOT_VALID  New type of import statement: import static com.elsevier.ew.ErrorConstants.*;  Both static attributes and methods

Varargs  Pass a variable number of arguments to a method  Like the C function: printf("value: %d", 15);  Compiler now understands this syntax: public static int optellen(int args...) { int resultaat = 0; for(i = 0; i < args.length; i++) restultaat = resultaat + args[i]; }

Metadata  Newest addition, separate JSR  Clues for precompilers, testtools, e.d.  C# attribute syntax: [xxx]  Java public static int add(int... params) { // blah }

Conclusie  Gone through the JCP  Early access 2.2 is downloadable  Beta and Final release somewhere in 2004  Big names: Joshua Blog, Neil Gafter

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