I want to make a mod for Minecraft, and i have Java and JDK 7, because it's not compatible with Java 8. but the new Eclipse is for Java 8, and i can't find anywhere a Eclipse version for Java 7.
You can work with any JDK if your Eclipse supports the latest one. You need to install JDK7, then you go to Window, Preferences. Type installed in the field and choose Installed JREs. Then, give the path of your JDK. Finally, right click on your project, Properties, Java compiler and select the appropriate JDK and compiler compliance.
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I am a regular IntelliJ user, but most of my co-workers use Eclipse. A lot of them say the latest version of Eclipse "2020-09", which requires a JRE "higher than Java 8" in order to run, cannot be used to develop projects requiring JRE8.
This is pretty surprising to me, since I know it is possible to install multiple JDKs and JREs on one machine, I've done it plenty of times.
What is the typical way a person would configure Eclipse 2020-09 (already installed) to work on a project that requires a Java 8 JRE?
JRE 8 apps in eclipse workspace is possible by having the jre 8 jdk. It is true that in order to use eclipse 2020-09 you need java 11+ jdk/jre, but making projects that support jre 8 is still possible.Even I still use 2020-06 and before. Here is a method you could use to get JRE 8 implemented back in your project. Although you can change the defaults, this one will help you change the environment back to java 8 for 1 project.
Right click the library named somthing like "JRE system library[JavaSE-11]". Press properties. This is what you will see JRE System Library chooser image
Choose "Alternate JRE" then click "Installed JREs"Step Image
Press "Add" then you will see 3 options. Choose standard VM. Find your java 8 jdk directory. Usually it is something like C:\Program Files\Java\jdk1.8.0_251.
You can configure the default arguments for your jvm runtime. Then simply hit ok,select the jdk-8 library and close it. Then choose alternate jre again and in the drop-down choose jdk-1.8.0 or some name like that. This will only work if you also have java 8 installed alongside java 11 that is configured properly JDK
You can use Java 11 to start the Eclipse 2020-09 and configure a project to compile with Java 8. The problem is if you want a Eclipse plugin that uses CORBA for example. This module was removed from Java 11 earlier. In this case, I recommend to use Eclipse 2020-06.
Earlier versions of 2020-09 was working with Java 8. I had it, too. Then I updated and I got the same error message like you.
I propose to use an older one or to install JRE 11 and set the JAVA_HOME env variable to it.
The inside the IDE you can set java 8 like an JDK and develope your project with Java 8 while eclipse is running with 11.
I had java version 8 previous and my eclipse worked just fine. But now I have java version 7 and I can't open eclipse on my computer. What should I do? please help.
I think there are two options:
Upgrade to Java version 8 (or newer).
If you can't do that, downgrade to a version of eclipse that supports Java 7. eclipse 4.5 (Mars) (or earlier as noted on the linked page), as of eclipse 4.6 (Neon) Java 8 is required.
I feel I should note that newer versions of Java (and eclipse) can still target Java 7 (and many earlier versions).
But now I have java version 7 and I can't open eclipse on my computer. What should I do?
Use versions that work together. When you for example look at your second screen shot, it says something like "requiredJavaVersion=1.8" or so.
In other words: you can't just come in and run eclipse with any version of java.
The other answer gives you the required details.
And a final note here: in case you tried to start eclipse with that older JVM in order to "allow" to ensure that eclipse won't allow "java 8" stuff in a project: that isn't the right way then. Instead: eclipse allows you to "define" JDKs to be used for your project. So you can easily tell eclipse: "I have a Java7 jdk sitting here, please use that for project X".
You do not need to run eclipse itself with a Java7 JVM in order to use a Java7 JDK for an eclipse project!
There will be a file under the Eclipse installation directory named as eclipse.ini.
It will launch the eclipse for that specific jdf and you can change the path to your jdk7.
Hope it helps.
It depends basically on which version of the eclipse you have.
If you have eclipse 4.6(Neon) or the latest version, then you must need a newer JDK version of Java (>=1.8 which you need to download). Or If you want to roll back to an older version of Eclipse then consider downloading eclipse 4.5(Mars).
Or If you have an eclipse version of 4.5(Mars) or older then see in eclipse.ini
-Dosgi.requiredJavaVersion = 1.8 and change it to -Dosgi.requiredJavaVersion = 1.7 which can be found in the folder containing eclipse.exe file.
Can you define anywhere in your Java Project which JRE/JDK version should it pick up?
In eclipse when I choose the project >> right click >> Java Compiler and check the "Compiler compliance level" I see a certain version marked (1.7,1.6 etc). How is this chosen?
Or is this entirely just dependent on what JDK/JRE runtime version your server (tomcat) is using?
Thanks
Short answer:
No, you can not identify the version of java that will be "picked up" at runtime.
More of an Answer:
There are three Java versions that come into play when building and running something using Java.
The source version. This is the version of Java to which the source of the project complies. When compiling, you can pass a "source" (try google search for "set java source level") parameter to identify this version. In practice, I don't know the value of this.
The target version. This is the version of Java to which the compiled result will comply. As with "source version" you can pass this as a parameter to the compiler.
Runtime version. This is the version of java that is actually installed on the host that is running the compiled java (the byte codes). You can never configure this at compile time since this is the thing that is installed on the runtime host.
There are some caveats.
The source and target version numbers must be equal to or less than the version of the java compiler that is actually compiling the java source. For example, you can choose target version 1.7 if you are compiling using a version 1.8 java compiler. You may not choose target version 1.8 if you are compiling using version a 1.7 java compiler.
It is possible to install multiple versions of java on a host. It is not possible to choose which version of java tomcat will use to execute your application since the version of java that will be used by tomcat is the version of java that is running tomcat.
It is chosen in that drop down menu, you can set it to whatever you'd like. However, you must have that version installed on your system/server in order for the project to function correctly. If you go to Window->Preferences->Java->Installed JREs, you can see which JREs you have installed. When you create a new server element in eclipse, you can also set the JRE of the runtime, and just make sure it matches the version of your project.
I have been having problems with appcompat_v7, someone told me to use Android-21 target. An error with that got me told to use JDK 1.8. I currently have JDK 1.6 installed. How do I switch Eclipse over to use JDK 1.8? I see no place to set the JDK path. The other time this question was asked, the questioner was referred to the JRE settings ... but the JDK is not the JRE, there are two separate paths. How do I get Eclipse to use the new JDK?
Project Menu > Properties menu item > Java Compiler > Compiler Compliance Level
Select your Java version from the pulldown menu. Obviously, you'll need to install Java 1.8 first to get it to show up as an installed version.
I already researched on how to install Eclipse Luna. One of the things to consider before installing Eclipse is to choose the JDK (planning to use JDK 8). It said that it is recommend that if I have an older version of Java, I need to uninstall it. But here's the problem: I don't know which I should uninstall. Here is the list of installed versions in my control panel (Windows 7 64bit):
Java 7
Java(TM) 6 Update 45
Java(TM) SE development kit 6 (i think this one but what's with (TM)?)
It is strongly recommended to specify what JVM (preferably a JDK) Eclipse should run in, via the eclipse.ini file. That way you can have any number of JDKs and/or JREs without problem. In fact, Eclipse also allows you to have multiple Java versions on your machine and each project in Eclipse can dictate exactly which one it uses. You can easily mix-and-match projects that use different Java versions, and they're all independent of the JVM that Eclipse itself is running in.
run java -version at the command line to see which one is in your PATH. This is the one that will run the Eclipse workspace.
Unless you have clear requirements to use older Java versions, I would recommend to uninstall all of them. And just have the latest JRE or better JDK installed.
In my case, I have a JRE to run the Eclipse workspace that is maintained by the Admin people and a private JDK (to provide additional tools, such as javadoc) to support the software development. You can have several Java versions installed (without having them in the PATH environment listed). You can point to them in the workspace settings or in specific Eclipse projects, e.g., to use a Java 6 for a certain project.
I think Eclipse Luna needs Java 7.
A Java 7 JRE/JDK is required for most of the Luna package downloads based on Eclipse 4.4.
In my opinion you can uninstall Java(TM) 6 Update 45 & Java(TM) SE development kit 6