Enhancements in
Packages java.lang.* and java.util.*

Enhancements in JDK 5.0
Enhancements in J2SDK 1.4
Enhancements in J2SDK 1.3

Enhancements in JDK 5.0

J2SE Development Kit 5.0 has several enhancments in the java.lang.* and java.util.* packages, including:

ProcessBuilder - The new ProcessBuilder class provides a more convenient way to invoke subprocesses than does Runtime.exec. In particular, ProcessBuilder makes it easy to start a subprocess with a modified process environment (that is, one based on the parent's process environment, but with a few changes).
Formatter - An interpreter for printf-style format strings, the Formatter class provides support for layout justification and alignment, common formats for numeric, string, and date/time data, and locale-specific output. Common Java types such as byte, java.math.BigDecimal , and java.util.Calendar are supported. Limited formatting customization for arbitrary user types is provided through the java.util.Formattable interface.
Scanner - The java.util.Scanner class can be used to convert text into primitives or Strings. Since it is based on the java.util.regex package, it also offers a way to conduct regular expression based searches on streams, file data, strings, or implementors of the Readable interface.
Concurrency Utilities The java.util.concurrent, java.util.concurrent.atomic, and java.util.concurrent.locks packages provide a extensible framework of high-performance, scalable, thread-safe building blocks for developing concurrent classes and applications, including thread pools, thread-safe collections, semaphores, a task scheduling framework, task synchronization utilities, atomic variables, and locks. Additionally, these packages provide low-level primitives for advanced concurrent programming which take advantage of concurrency support provided by the processor, enabling you to implement high-performance, highly scalable concurrent algorithms in Java to a degree not previously possible without using native code. For more information, refer to JSR 166 .
Collections Framework Enhancements - There are many enhancements to the Collections framework.
Instrumentation - The new java.lang.instrument package provides services that allow Java programming agents to instrument programs running on the Java virtual machine by modifying methods' bytecodes at runtime.
Threads - The java.lang.Thread class has the following enhancements:
- Thread priority handling has changed.
- Thread.State enum class and the new getState() API are provided for querying the execution state of a thread.
- The new thread dump API - the getStackTrace and getAllStackTraces methods in the Thread class - provides a programmatic way to obtain the stack trace of a thread or all threads.
- The uncaughtExceptionHandler mechanism, previously available only through the ThreadGroup class, is now available directly through the Thread class.
- A new form of the sleep() method is provided which allows for sleep times smaller than one millisecond.

Enhancements in Java 2 SDK v1.4

Java 2 SDK v1.4 offered several significant enhancements to the functionality in the java.lang.* and java.util.* packages, including

Preferences API - The preferences API, implemented by package java.util.prefs, allows applications to store and retrieve user and system preference and configuration data. This data is stored persistently in an implementation-dependent backing store. The Preferences API is intended to replace most common uses of class java.util.Properties, rectifying many of its deficiencies, while retaining its light weight.
Logging API - The Java Logging API facilitates software servicing and maintenance at customer sites by producing log reports suitable for analysis by end users, system administrators, field service engineers, and software development teams. The Logging APIs capture information such as security failures, configuration errors, performance bottlenecks, and/or bugs in the application or platform. The core package includes support for delivering plain text or XML formatted log records to memory, output streams, consoles, files, and sockets. In addition, the logging APIs are capable of interacting with logging services that already exist on the host operating system.
Regular Expressions - New package java.util.regex contains classes for matching character sequences against patterns specified by regular expressions.
Chained Exception Facility - This is a new facility that provides a common API to record the fact that one exception caused another, to access causative exceptions, and to acess the entire "causal chain" as part of the standard stack backtrace, ensuring that preexisting programs will provide this information with no additional effort on the part of their authors.

Enhancements in Java 2 SDK 1.3

Version 1.3 of the Java 2 SDK includes the following enhancements:

Classes java.lang.Math and java.lang.StrictMath
New Timer API
Enhanced Collections Framework
Virtual Machine Shutdown Hooks
New URL JAR File Caching

Classes `java.lang.Math` and `java.lang.StrictMath`

The Java 2 Platform now contains two clases which provide API for performing general numeric operations.

java.lang.StrictMath - Class java.lang.StrictMath has the same API as old class java.lang.Math, which was present in previous versions of the Java platform. Unlike class Math, however, StrictMath is defined to return bit-for-bit reproducible results in all implementations.
java.lang.Math - Class java.lang.Math provides the same set of API as does class StrictMath. However, unlike some of the numeric functions of class StrictMath, all implementations of the equivalent functions of class Math are not defined to return the bit-for-bit same results, but can vary within specified constraints. This permits better-performing implementations where strict reproducibility is not required.

New Timer API

Two new classes have been added to the Java 2 Platform to provide an API for a timer facility which can be used for purposes such as animations, human interaction timeouts, on-screen clocks and calendars, work-scheduling routines, reminder facilities, and more.

Countdown.java is a simple demo application that uses the new Timer API.

Enhanced Collections Framework

The Collections Framework has these new convenience APIs:

Added java.util.Collections.singletonList and java.util.Collections.singletonMap. Previously, there was a convenience implementation for singleton Set, but no corresponding implementation for List and Map. Both of these implementations proved desirable in practice.
Added java.util.Collections.EMPTY_MAP. Previously, there were constant convenience implementations for the empty Set and List, but no corresponding implementation for Map.

The following special-purpose implementation has also been added:

Added Map constuctor for WeakHashMap. The Map interface dictates that most Map implementations should have a "copy constructor" that takes a Map argument. WeakHashMap lacked such a constructor in the 1.2 release.

Virtual Machine Shutdown Hooks

Sophisticated applications often require the ability to perform specific actions when the virtual machine shuts down, whether due to voluntary exit or involuntary termination. Typical actions include cleanly closing down network connections, saving session state, and deleting temporary files. Every major operating system provides the means for native applications to do this, though of course the details vary from platform to platform. Three methods have been added to java.lang.Runtime to provide a simple and portable interface to these facitilies. The new methods are:

In addition, the Runtime.exit method has been revised. For more information, see Design of the Shutdown Hooks API.

New URL JAR File Caching

The API of classes java.util.zip and java.util.jar have been enhanced with the addition of the following:

The previous implementation of caching downloaded Jar files created problems for long-running server application and for RMI. Each open JarURLConnection creates a temporary local file that holds Jar-file date, and a JarFile object is created on top of the temporary file. Because the open file handle/descriptor on each temporary file was never closed, the files could quickly take up disk space for long-running server applications. The new API provides a solution for this problem by supporting a new "delete-on-close" mode for opening Zip and Jar files.

Enhancements in Packages java.lang.* and java.util.*