Why won't eclipse switch the compiler to Java 8?
Two things:
First, JRE is not the same as the JDK. If you do have the JDK, you need to configure eclipse to point to that in your settings.
Second, in your screenshot above, your compiler compliance level is set to 1.7. This will treat all your code as if it's using Java 1.7. Change this to 1.8 to fix your error.
You will need to have Eclipse Luna in order to get support for Java 8, but you can add it to Kepler SR2 if you want. I'd try with Luna and the above suggestions before you go any further. See this reference.
Once you get Luna, your JAVA_HOME variable should be enough to get Eclipse to recognize JDK 8. If you want to specify an additional JDK, you can add a new Java System Library by going to:
Project -> Properties -> Java Build Path -> Libraries -> Add Library -> Java System Library
and navigating to a valid location for the JDK 8.
You can download your platform's JDK 8 here
It cause eclipse kepler SR1 does not support new Java™ 8 language enhancements like lambda expression.
From information here: http://www.eclipse.org/downloads/java8/
I think you should use kepler SR2 with support plugin, or change to Eclipse Luna.
Updated link 16/09/2016: https://wiki.eclipse.org/JDT/Eclipse_Java_8_Support_For_Kepler
I had the same problem even though I had:
a freshly downloaded JDK 1.8.0
JAVA_HOME is set
java -version on command line reports 1.8
Java in control panel is set to 1.8
downloaded Eclipse Mars
Eclipse only let me choose a compiler compliance level op to 1.7 in the compiler preferences, even though my installed JRE is 1.8.0. I also couldn't see a 1.8 in the Execution Environments underneath Installed JREs, only a JavaSE-1.7 (which I haven't even got installed!). When I clicked on that, it shows "jdk1.8.0" as a compatible JRE, so I selected that, but still no change.
Then I unzipped Eclipse Mars into a brand new directory, created a new project, and now I can select 1.8, hurrah! That greatly reduced the "Duplicate methods named spliterator..." errors I was getting when compiling my code under Java 1.8, however, there is still one left:
Duplicate default methods named spliterator with the parameters () and () are inherited from the types List and Set.
However, that's likely because I'm extending AbstractList and implementing Set, so I've fixed that for now by removing the implements Set because it doesn't really add anything in my case (other than signifying that my collection has only unique elements)