Javac 1.7 版无法为目标 1.7 构建

问题描述：

我正在尝试在 Linux Mint 系统上使用 Sun Java JDK 1.7.0_17 编译 Java 代码，但我遇到了这个问题.

I am trying to compile Java code, with Sun Java JDK 1.7.0_17, on a Linux Mint system, but I'm getting this problem.

$ javac  -version -target 1.7 
javac 1.7.0_17
javac: invalid target release: 1.7

-target 1.6 也不起作用.Target 1.5 有效，但我遇到了版本问题，

-target 1.6 doesn't work either. Target 1.5 works, but I get a version problem as such,

$ javac  -version -target 1.5 HelloWorld.java 
javac 1.7.0_17
HelloWorld.java:2: cannot access java.lang.Object
bad class file: /usr/lib/jvm/jdk1.7.0_17/jre/lib/rt.jar(java/lang/Object.class)
class file has wrong version 51.0, should be 49.0
Please remove or make sure it appears in the correct subdirectory of the classpath.
class HelloWorldApp {
^
1 error

在 sun java 目录之外是否有可用的 java 目标列表?

Is there somewhere a list of available java targets outside of the sun java directories?

我没有指定 ClassPath 或 Javahome，设置它们也无济于事.jcontrol 没有帮助.我也试过 1.7.0_15，结果相似.

I have no ClassPath or Javahome specified, and setting them doesn't help. jcontrol doesn't help. I have also tried with 1.7.0_15, with similar results.

答

我解决了一个涉及 Ubuntu、Netbeans 和两个 JDK:openJDK 和 oracleJDK 的类似问题.有问题的(旧的和不相关的)文件最终位于/usr/java/packages 中并被简单地删除.

I chased down a similar issue involving Ubuntu, Netbeans and two JDK's: openJDK and oracleJDK. The offending (old and irrelevant) files were eventually located in /usr/java/packages and simply deleted.

我收到了:

# javac -version hello.java
javac 1.7.0_21
hello.java:3: cannot access java.lang.Object
bad class file: /usr/lib/jvm/java-7-oracle/jre/lib/rt.jar(java/lang/Object.class)
class file has wrong version 51.0, should be 49.0
Please remove or make sure it appears in the correct subdirectory of the classpath.
public class hello {
       ^
1 error

更重要的是，我通过以下方式找到了有问题的文件:

More importantly, I located the offending files with:

# javac -verbose -version hello.java

-verbose 选项列出了类文件的搜索路径.

The -verbose option lists the search path for class files.

我在调查期间探索的其他领域包括:

Other areas explored during my investigation were:

环境变量JAVA_HOME的值与#echo $JAVA_HOME
环境变量PATH与#echo $JAVA_HOME的值
环境变量CLASSPATH的值与#echo $JAVA_HOME
带有 #update-alternatives --config javac
带有 #galternatives 的更新替代方案
Netbeans 使用的 JDK 设置在/usr/local/netbeans-7.3/etc/netbeans.conf 中，带有 netbeans_jdkhome= 开关.请注意，此开关会覆盖 update-alternatives

the value of environment variable JAVA_HOME with #echo $JAVA_HOME
the value of environment variable PATH with #echo $JAVA_HOME
the value of environment variable CLASSPATH with #echo $JAVA_HOME
the update-alternatives with #update-alternatives --config javac
the update-alternatives with #galternatives
the JDK used by Netbeans set in /usr/local/netbeans-7.3/etc/netbeans.conf with the netbeans_jdkhome= switch. Note that this switch overrides update-alternatives

Javac 1.7 版无法为目标 1.7 构建

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