Setting JDK in Eclipse

Question

I have two JDKs  for Java 6 and 7   I want to build my project using both  Initially we only built against 1 6  I see in my project setting I can select 1 5  1 6 1 7 as the compiler level   How are these options added to the IDE  I never installed Java 1 5  Suppose I wanted Java 1 4  How would I get this to appear in the list  I have added two different JREs in my IDE preferences  but these are not what appears in the dropdown

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Eclipse s compiler can assure that your java sources conform to a given JDK version even if you don t have that version installed   This feature is useful for ensuring backwards compatibility of your code   Your code will still be compiled and run by the JDK you ve selected

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Configuring JDKs   Windows -  Preferences -  Installed JREs  to configured the installed JDKs Project Properties  Java Compiler  Enable project specific settings  or configure Workspace settings   JDK Compliance Project Properties  Java Build Path  Libraries  Add Library  JRE system library  Workspace default or Alternate JRE  one of the JREs configured in    Maven  BUT IF you are using maven  provided that you have your latest JRE  Windows Preferences Installed JREs  -for example JDK 1 8  You can select the level 1 6  1 7  1 8 by configuring the maven-compiler-plugin source and target attributes  like this               lt plugin gt                   lt artifactId gt maven-compiler-plugin lt  artifactId gt                   lt version gt 3 3 lt  version gt                   lt configuration gt                       lt source gt 1 8 lt  source gt                       lt target gt 1 8 lt  target gt                   lt  configuration gt               lt  plugin gt    And ideally  if you have a parent pom  you can do it for all the modules  Eclipse projects  in the parent pom  in one single place   Source and Target If we want to use the Java 8 language features the    source should be set to 1 8  Also  for the compiled classes to be compatible with JVM 1 8  the    target value should be 1 8    Updating JRE library that is broken in many projects at once  with Maven   Rather than updating one by one the JRE library  let Maven do it for you   Selecting the projects and right-clicking for Maven -  Update Project  will set the system library to the path of the installed JDK  in case the paths are broken  because you installed a new JDK or imported from another computer  etc   and set the JDK compliance according to the maven source and target setting in the pom

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You manage the list of available compilers in the Window - gt  Preferences - gt  Java - gt  Installed JRE s tab   In the project build path configuration dialog  under the libraries tab  you can delete the entry for JRE System Library  click on Add Library and choose the installed JRE to compile with   Some compilers can be configured to compile at a back-level compiler version   I think that s why you re seeing the addition version options

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JDK 1 8 have some more enrich feature which doesn t support to many eclipse    If you didn t find java compliance level as 1 8 in java compiler  then go ahead and install the below eclipse 32bit or 64 bit depending on your system supports       Install jdk 1 8 and then set the JAVA HOME and CLASSPATH in environment variable  Download eclipse-jee-neon-3-win32 and unzip    supports to java 1 8 Or download Oracle Enterprise Pack for Eclipse  12 2 1 5  and unzip   Supports java 1 8 with 64 bit OS Right click your project   properties Select    Java Compiler    on left and set java compliance level to 1 8  select from the dropdown 1 8  Try running one java program supports to java 8 like lambda expression as below and if no compilation error  means your eclipse supports to java 1 8  something like this   interface testI      void show         class A implements testI      public void show            System out println  Hello               public class LambdaDemo1       public static void main String   args            testI test             test  new A            test show              test      - gt System out println  Hello how are you       lambda          test show

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Some additional steps may be needed to set both the project and default workspace JRE correctly  as MayoMan mentioned  Here is the complete sequence in Eclipse Luna    Right click your project   properties Select    Java Build Path    on left  then    JRE System Library     click Edit    Select  Workspace Default JRE  Click  Installed JREs  If you see JRE you want in the list select it  selecting a JDK is OK too  If not  click Search     navigate to Computer   Windows C    Program Files   Java  then click OK Now you should see all installed JREs  select the one you want Click OK Finish a million times   Easy     not

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To tell eclipse to use JDK  you have to follow the below steps    Select the Window menu and then Select Preferences  You can see a dialog box  Then select Java ---  Installed JRE   s Then click Add and select Standard VM then click Next In the JRE home  navigate to the folder you   ve installed the JDK  For example  in my system my JDK was in C  Program Files Java jdk1 8 0 181    Now click on Finish    After completing the above steps  you are done now and eclipse will start using the selected JDK for compilation

[eclipse] Setting JDK in Eclipse

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