This document describes Java™ SE 6 compatibility with J2SE 5.0 under the following topics:
The compatibility documents listed below track incompatibility between adjacent Java versions. For example, this compatibility page reports only Java SE 6 incompatibilities with J2SE 5.0, and not with previous versions. To examine Java SE 6 incompatibilities with earlier Java versions, you must trace incompatiblities through the files listed below, in order.
See the Java Language Specification Maintenance Page for a summary of changes that have been made to the specification of the Java programming language since the publication of the Java Language Specification, Second Edition .
Java SE 6 is upwards binary-compatible with J2SE 5.0 except for the incompatibilities listed below. Except for the noted incompatibilities, class files built with version 5.0 compilers will run correctly in JDK 6.
Some early bytecode obfuscators produced class files that violated the class file format as given in the virtual machine specification. Such improperly formatted class files will not run on the JDK virtual machine, though some of them could have run on earlier versions of the virtual machine. To remedy this problem, regenerate the class files with a newer obfuscator that produces properly formatted class files.
Java SE 6 does not support downward source compatibility. If source files use new language features or Java SE platform APIs, they will not be usable with an earlier version of the Java platform.
In general, the policy is as follows, except for any incompatibilities listed further below:
Maintenance releases (such as 1.4.1, 1.4.2) do not introduce any new language features or APIs. They will maintain source-compatibility with each other.
Functionality releases and major releases (such as 1.3.0, 1.4.0, 5.0) maintain upwards but not downwards source-compatibility.
Deprecated APIs are interfaces that are supported only for backwards compatibility. The
javac compiler generates a warning message whenever one of these is used, unless the
-nowarn command-line option is used. It is recommended that programs be modified to eliminate the use of deprecated APIs, although there are no current plans to remove such APIs entirely from the system with the exception of JVMDI and JVMPI.
Some APIs in the
sun.* packages have changed. These APIs are not intended for use by developers. Developers importing from
sun.* packages do so at their own risk. For more details, see Why Developers Should Not Write Programs That Call sun.* Packages.
Java SE 6 is strongly compatible with previous versions of the Java platform. Almost all existing programs should run on Java SE 6 without modification. However, there are some minor potential source and binary incompatibilities in the JRE and JDK that involve rare circumstances and "corner cases" that we are documenting here for completeness.
JVMDI was removed and JVMPI was disabled in Java SE 6
JVM™ TI is defined by JSR-163. An implementation was released in J2SE 5.0. JVM™ TI replaces the functionality in JVMDI and JVMPI. JVMDI was deprecated in J2SE 5.0. It has been removed from Java SE 6.
JVMPI was deprecated in J2SE 5.0. It has been disabled in Java SE 6, and it will be removed in the next release.
Java SE 6 includes a new verification scheme and a new class file format to support this scheme
By default the Java compiler, javac, generates class files for the new verification scheme (class file version 50.0). While this new class file version has been designed to be backwards compatible, vendors of byte code manipulation tools should start updating their tools to support the new class file format.
java.nio.channels.FileLock class checks for files already locked by other
Java SE 6 throws an
OverlappingFileLockException if an application attempts to lock a region that overlaps a region locked through another
FileChannel instance. Previous versions did not check for file locks obtained by other
By default the
java.nio.channels.FileChannel.lock method checks if the requested lock overlaps with a region held by this Java virtual machine.
Java SE 6 has added the system property
sun.nio.ch.disableSystemWideOverlappingFileLockCheck to control
java.nio.channels.FileChannel.lock file checking behavior, as follows:
java.nio.channels.FileChannel.lockchecks for overlapping file locks obtained using this
FileChannelinstance only. Locks acquired by other
FileChannelinstances to the same file are not checked.
java.nio.channels.FileChannel.lockchecks for overlapping file locks from all
FileChannelinstances, according to the specification.
sun.nio.ch.disableSystemWideOverlappingFileLockCheck system property exists to provide compatibility with J2SE 1.4 and 5.0, which do not implement the JVM-wide overlapping file lock check.
Java SE 6 defaults to the
sun.awt.x11.XToolkit on Solaris and other Unix-based platforms
Users can use the MToolkit by setting the
awt.toolkit property to
Java SE 6 Properly Rejects Illegal Casts
The cast implementation adheres more closely to the Java Language Specification. In general, this means that
javac will accept more programs. However, in some rare cases,
javac can now reject previously accepted, yet incorrect programs.
Non class files have been moved from
rt.jar in Java SE 6
Java applications that specify
-Xbootclasspath:<path to rt.jar> and request any resource files will fail since these resources now reside in a different jar file called
java.beans.EventHandler Enforces Valid Arguments
java.beans.EventHandler Enforces Valid Arguments
java.beans.EventHandler documentation more completely describes the following:
EventHandlerdoes not enforce valid arguments. The
listenerInterfacearguments need to be non-null for it to work correctly. In Java SE 6, The
createmethods now check these arguments and immediately throw an
IllegalArgumentExceptionif any arguments are null.
eventPropertyNamecauses the event to be passed to the target action.
eventPropertyNameand notes that
target/action/listenerInterfaceneeds to be non-null.
constructormethods can throw an
These changes force
create to throw a
nullPointerException immediately with null target/action, rather than later on. While the exception is now thrown at a different time, the exception is still the same and is thrown at a point where code logic can catch it and appropriately deal with it.
Specifying constraints on
SpringLayout was order dependent
SpringLayout specifies three Springs along each axis which dictate the size and position of a component. Only two Springs are needed along each axis, with the third being derived. If three Springs are specified, the layout is considered overly constrained and one of the Springs is dropped. Currently, the behavior for determining which Spring to drop is not intuitive and leads to ordering problems.
In Java SE 6,
SpringLayout maintains the order in which springs have been set. As a result, specifying springs is no longer order-dependent. Support for centering and aligning along the baseline has also been added.
Programs affected by this change can contain statements that were redundant in J2SE 5.0.
constraints.setX(xSpring); constraints.setConstraint("East", eastSpring);
In J2SE 5.0, the
setX call in effect resulted in nothing, in Java SE 6, the
setX call is meaningful and different behavior will result.
Double buffering enhancements
Currently, there can be a noticable delay between the time a window is unobscured and the time the window is repainted.
In Java SE 6, Swing provides full double buffering. For each window, Java SE 6 maintains an offscreen buffer that remains in sync with the onscreen window buffer. Any time a window is unobscured, Swing copies from the back buffer directly to the screen. Swing also manages repainting for
JWindow, JDialog, JApplet, JFrame and other heavyweight components in the Swing package. New methods have been added to
RepaintManager to manage this activity.
Applications which can rely on Swing to do painting on an expose event can be affected. In Java SE 6, Swing classes might not paint an expose event if they can instead refresh the screen from the backbuffer.
Java SE 6 drag behavior is consistent with Microsoft Windows drag behavior
In the current Swing implementation of Drag and Drop, we require users first click on an object to select it, and then to click again on the same object before they can initiate a drag operation. This is not intuitive behavor for users who are used to using a single click to both select an object and then start a drag operation.
Java SE 6 has changed the appropriate Swing Classes to implement the single click drag model. Documentation has been updated for affected components to describe how drag gestures are recognized.
The solution to this problem has required making some small potentially incompatible changes in the implementation of our drag and drop support. Note that none of these incompatibilities will affect components where drag support is turned off, which is the default. Also, these will not affect most users even with drag support turned on.
JTrees with drag enabled will now consider editing only after receiving a mouse-released event. Previously, certain press events (such as those not part of a drag gesture) could trigger editing. For consistency, to allow selection changes, and for drag-and-drop to properly occur on the press event; editing can now only start upon the release. With drag disabled, selection will continue to function as it has in the past.
JTreecontain a boolean method called
shouldSelectCell(). This method returns whether the current cell should be selected. It is called once editing is started. It also can be used to determine when editing has started, in order to configure the editor. When drag is enabled in a component, a cell MUST be selected before it can be dragged. For this reason, Java SE 6 ignores
shouldSelectCelland always selects cells when drag is enabled. However, Java SE 6 still calls
shouldSelectCellafter it starts editing, for those users expecting it for side-effects. There is no change if drag is disabled.
JDK1_1AttachArgs no longer used
JDK1_1AttachArgs data structures are no longer used, but were present in the
jni.h file and corresponding documentation.
JDK1_1AttachArgs has been removed from
JDK1_1InitArgs has been moved from
jvm.h where it is used internally.
Password no longer visible in Java SE security tools
The JDK tools
kinit will no longer echo passwords to the screen. Users will need to enter a password twice when entering a new password or changing an existing password. Scripts that use keytool to either create a new keystore or create a new key in the keystore using a password unique from the keystore password will need to be updated.
jar will preserve file modification dates and times during extract
Files and directories extracted from a jar archive will now have their timestamp set to match the timestamp of the corresponding file/directory in the jar archive. Prior to Java SE 6, files and directories extracted from a jar archive were given the date and time of the extraction. A system property,
sun.tools.jar.useExtractionTime=true, is provided so that the Java SE 5.0 and earlier behavior can be obtained. The default value of this property in Java SE is
The Duration and
XMLGregorianCalendar equals() methods now return
javax.xml.datatype.XMLGregorianCalendar.equals() methods now return
false instead of throwing a
NullPointerException for a null parameter.
The double-slash character string ("//") is reserved in JMX ObjectNames
JSR 255 plans to use "//" in the domain part of an
javax.management.ObjectName as a separator for "cascading". While JSR 255 is not part of Java SE 6, it is recommended that the domain part of an
ObjectName not contain the string "//" to avoid future compatibility issues.