Java 1 5 Effective Java Fawzi Emad Chau Wen Tseng Department of Computer Science University of Maryland College Park Java 1 5 Tiger Description Released September 2004 Largest revision to Java so far Goals Less code complexity Better readability More compile time type safety Some new functionality generics scanner New Features in Java 1 5 Generic types Scanner Autoboxing unboxing Enhanced for loop Variable number of arguments varargs Enumerated types Static imports Annotations Generics Motivating Example Problem Utility classes handle arguments as Objects Objects must be cast back to actual class Casting can only be checked at runtime Example class A class B List myL new List myL add new A Add an object of type A B b B myL get 0 throws runtime exception java lang ClassCastException Generic Types Parameterized types with type parameter Parameterize classes interfaces methods by types Parameters defined using x notation Parameters replaced at compile time with casts Provide compile time type safety Support in java util Example public class foo x y z public class List String Generics Usage Using generic types Specify type parameter for utility class Automatically performs casts Can check class at compile time Example class A class B List A myL new List A myL add new A Add an object of type A A a myL get 0 myL element class A B b B myL get 0 causes compile time error Scanner Iterator for Provides methods for input parsing Supports String nextLine int nextInt Throws InputMismatchException if wrong format Example old approach to scanning input BufferedReader br new BufferedReader new InputStreamReader System in String name br readLine new approach using scanner Scanner in new Scanner System in String name in nextLine Autoboxing Unboxing Automatically convert primitive data types Data value Object of matching class Data types classes converted Boolean Byte Double Short Integer Long Float Example ArrayList myL new ArrayList myL add 1 previously myL add new Integer 1 Integer X new Integer 2 int y X previously int y X intValue Enhanced For Loop For loop handles Iterator automatically Test hasNext then get cast next Example Iterator it myL iterator old usage of Iterator while it hasNext Integer num Integer it next do something with num for Integer num myL new enhanced for loop do something with num Variable of Arguments Varargs Method allow variable of arguments vararg Arguments automatically stored in array Only single vararg allowed must be last argument Example void foo int x String myL for String str myL do something with str foo 1 car boat foo 2 car boat plane foo 3 String x Enumerated Types New type of variable with set of fixed values Establishes all possible values by listing them Supports values valueOf name compareTo Example public Class Color old approach to enumeration private int c public static final Color Black new Color 1 public static final Color White new Color 2 public enum Color Black White new enumeration Color myC Color Black for Color c Color values System out println c Static Import Import static members of package Example imports static members of package import static java lang Math ceil imports all static members of package import static java lang Math double x y x ceil y can use method name directly Annotations Add annotations metadata using Annotate types methods fields for documentation code generation runtime services Provides built in custom annotations Target Overrides Documented Can control availability of annotations Source code class file runtime in JVM Example author CMSC132Coder public final class AnnotationsTest Overrides public String toString int i return x Effective Java Title Effective Java Programming Language Guide Author Joshua Bloch Contents Useful tips for Java programming Effective Java Topics 1 Creating and Destroying Objects 2 Methods Common to All Objects 3 Classes and Interfaces 4 Substitutes for C Constructs 5 Methods 6 General Programming 7 Exceptions 8 Threads 9 Serialization Creating and Destroying Objects Consider providing static factory methods instead of constructors Enforce singleton property with a private constructor Enforce noninstantiability with a private constructor Avoid creating duplicate objects Eliminate obsolete object references Avoid finalizers Methods Common to All Objects Obey the general contract when overriding equals Always override hashCode when you override equals Always override toString Override clone judiciously Consider implementing Comparable Classes and Interfaces Minimize the accessibility of classes and members Favor immutability Favor composition over inheritance Design and document for inheritance or else prohibit it Prefer interfaces to abstract classes Use interfaces only to define types Favor static member classes over nonstatic Methods Check parameters for validity Make defensive copies when needed Design method signatures carefully Use overloading judiciously Return zero length arrays not nulls Write doc comments for all exposed API elements General Programming Minimize the scope of local variables Know and use the libraries Avoid float and double if exact answers are required Avoid strings where other types are more appropriate Beware the performance of string concatenation Refer to objects by their interfaces Prefer interfaces to reflection Use native methods judiciously Optimize judiciously Adhere to generally accepted naming conventions Exceptions Use exceptions only for exceptional conditions Use checked exceptions for recoverable conditions and run time exceptions for programming errors Avoid unnecessary use of checked exceptions Favor the use of standard exceptions Throw exceptions appropriate to the abstraction Document all exceptions thrown by each method Include failure capture information in detail messages Strive for failure atomicity Don t ignore exceptions Threads Synchronize access to shared mutable data Avoid excessive synchronization Never invoke wait outside a loop Don t depend on the thread scheduler Document thread safety Avoid thread groups
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