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问题:

I'm having trouble with a brand new project in a brand new installation of Eclipse. Repro steps:

Download this version of Eclipse: http://www.eclipse.org/downloads/packages/eclipse-ide-java-developers/heliosr
Unzip to c:\program files\eclipse java
Launch Eclipse; choose a workspace
File > New > Java Project
Project name: Hello World. JRE: "Use an execution environment JRE: JavaSE-1.7"
Hit Next, go to the Libraries tab. The only entry is JRE System Library [JavaSE-1.7] (unbound). What does "unbound" mean? How do I fix it?
Hit Finish.

Expected: Brand new project works fine.

Actual: There are two errors:

The project cannot be built until build path errors are resolved HelloWord  Unknown Java Problem Unbound classpath container: 'JRE System Library [JavaSE-1.7]' in project 'HelloWord' HelloWord  Build path Build Path Problem

What am I doing wrong here?

Update: Perhaps I don't actually have the Java 7 JDK on my machine. How can I be sure?

Update 2: Looks like Java 7 is in fact not out yet. Sweet.

回答1:

1) Find out where java is installed on your drive, open a cmd prompt, go to that location and run ".\java -version" to find out the exact version. Or, quite simply, check the add/remove module in the control panel.

2) After you actually install jdk 7, you need to tell Eclipse about it. Window -> Preferences -> Java -> Installed JREs.

回答2:

To set JDK you can watch this video : how to set JDK . Then when you'll have JDK:

Right click on build path and select "Build Path"
Choose "Configure Build Path"
Click on "JRE System Library [JavaSE-1.7] (unbound)"
Edit it
Choose "Alternate JRE"
Click on "Installed JREs.." button
Press Add
Choose to add "Standard VM"
Choose JRE Home directory - usually it is locates in "C:\Program Files\Java\jre7" directory
Press "Finish"
Re-check newly appeared "Jre7": Verify that now when you edit "JRE System Library [JavaSE-1.7]" "Alternate JRE" is chosen for jre7.

回答3:

1)Go to configure build path . 2)Remove unbound JRE library . 3)Add library --> JRE System library .

Then project compile and done ..

回答4:

Have you actually downloaded and installed one of the milestone builds from https://jdk7.dev.java.net/ ?

You can have a play with the features, though it's not stable so you shouldn't be releasing software against them.

回答5:

Most of the time after the installation of Eclipse eclipse.ini is changed. If you change the jdk in eclipse.ini then eclipse will use this jdk by default.

Let's say you install a new version of Eclipse and you have forgotten to change the eclipse.ini related to the jdk. Then Eclipse finds a jdk for you. Let's say it is java 1.6 that was automatically discovered (you did nothing).

If you use maven (M2E) and you reference a 1.7 jdk then you will see the frustrating message. But normally it is not displayed because you configure the correct jdk in eclipse.ini.

That was my case. I made reference into the pom to a jdk that was not configured into Eclipse.

In the screenshot you can see that 1.7 is configured and seen by Eclipse. In this case, you should make reference into the pom to a jre that is compatible with 1.7! If not -> frustrating message!