I tried to build a project on netbeans when this error came up:

 javac: invalid target release: 1.6
 Usage: javac <options> <source files>
 where possible options include:
 -g Generate all debugging info
 -g:none Generate no debugging info
 -g:{lines,vars,source} Generate only some debugging info
 -nowarn Generate no warnings
 -verbose Output messages about what the compiler is doing
 -deprecation Output source locations where deprecated APIs are
 used
 -classpath <path> Specify where to find user class files
 -cp <path> Specify where to find user class files
 -sourcepath <path> Specify where to find input source files
 -bootclasspath <path> Override location of bootstrap class files
 -extdirs <dirs> Override location of installed extensions
 -endorseddirs <dirs> Override location of endorsed standards path
 -d <directory> Specify where to place generated class files
 -encoding <encoding> Specify character encoding used by source files
 -source <release> Provide source compatibility with specified release
 -target <release> Generate class files for specific VM version
 -version Version information
 -help Print a synopsis of standard options
 -X Print a synopsis of nonstandard options
 -J<flag> Pass <flag> directly to the runtime system

 BUILD FAILED (total time: 0 seconds)
 ==============================a useful answer:
Do you have JDK 1.6 installed? It sounds like you are running under 1.5. IIRC, later versions of Netbeans default to use version 1.6. To specify 1.5, right click your project, go to properties, and under sources, near the bottom of the window, change "Source Level" to 1.5. Alternatively, install 1.6 and/or configure netbeans to use it rather than 1.5.
 
 
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set the JAVA_HOME same as the eclipse default jdk