how do I get eclipse to use a different compiler version for Java

Question

It seems like this should be a simple task  with the options in the Preferences menu for different JREs and the ability to set different compiler and build paths per project  However  it also seems to simply not work   For example  I have my JAVA HOME set to a jre for Java 1 6  It s still not clear to me how Eclipse uses this  but it appears to be defaulting to this and not taking the project overrides  I have also installed Java 1 5  and added a JRE for this in eclipse in the Java- Installed JREs section   In my project  I ve set the compiler compliance level to 1 5  In the build path for the project  I ve added the System Library for the Java 1 5 JRE  However  I m getting compile errors for a class that implements PreparedStatement for not implementing abstract methods that only exist in Java 1 6 PreparedStatement  Specifically  the methods   setAsciiStream int  InputStream  long  and  setAsciiStream int  InputStream    Strangely enough  it worked when we were compiling it against Java 1 4  which it was originally written for  We added the JREs for Java 1 4 and referenced that system library in the project  and set the project s compiler level to 1 4  and it works fine  But when I do the same changes to try to point to Java 1 5  it instead uses 1 6   Any ideas why

User · Answer

First off  are you setting your desired JRE or your desired JDK   Even if your Eclipse is set up properly  there might be a wacky project-specific setting somewhere   You can open up a context menu on a given Java project in the Project Explorer and select Properties   Java Compiler to check on that   If none of that helps  leave a comment and I ll take another look

User · Answer

From the menu bar  Project -  Properties -  Java Compiler  Enable project specific settings  checked  Uncheck  use Compliance from execution environment       Select the desired  compiler compliance level   That will allow you to compile  1 5  code using a  1 6  JDK   If you want to acutally use a 1 5 JDK to produce  1 5  compliant code  then install a suitable 1 5 JDK and tell eclipse where it is installed via   Window -  preferences -  Installed JREs   And then go back to your project  Project -  properties -  Java Build Path -  libraries  remove the 1 6 system libaries  and  add library    -  JRE System LIbrary -  Alternate JRE -  The JRE you want   Verify that the correct JRE is on the project s build path  save everything  and enjoy

User · Answer

Just to clarify  do you have JAVA HOME set as a system variable or set in Eclipse classpath variables  I m pretty sure  but not totally sure   that the system variable is used by the command line compiler  and Ant   but that Eclipse modifies this accroding to the JDK used

User · Answer

Eclipse uses it s own internal compiler that can compile to several Java versions   From Eclipse Help   Java development user guide   Concepts   Java Builder     The Java builder builds Java programs using its own compiler  the Eclipse Compiler for Java  that implements the Java Language Specification     For Eclipse Mars 1 Release  4 5 1   this can target 1 3 to 1 8 inclusive   When you configure a project    project-name   gt  Properties  gt  Java Compiler  gt  Compiler compliance level   This configures the Eclipse Java compiler to compile code to the specified Java version  typically 1 8 today   Host environment variables  eg JAVA HOME etc  are not used   The Oracle Sun JDK compiler is not used

[java] how do I get eclipse to use a different compiler version for Java?

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