线程“main"中的异常java.lang.UnsupportedClassVersionError: a (Unsupported major.minor version 51.0)

问题描述：

我安装了 JDK7，一个简单的 hello word 程序可以编译，但是当我运行这个程序时，我得到了以下异常.

I installed JDK7, a simple hello word program gets compile but when I run this I got following exception.

Exception in thread "main" java.lang.UnsupportedClassVersionError: a (Unsupported major.minor version 51.0)
    at java.lang.ClassLoader.defineClass0(Native Method)
    at java.lang.ClassLoader.defineClass(Unknown Source)
    at java.security.SecureClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.access$100(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClassInternal(Unknown Source)

我在命令提示符下检查了 java -version，它显示了 Java 版本 1.4.2_03，但是当我尝试从 java.com 安装新的 Java 版本时，它说我推荐了 Java 7 版本.

I checked java -version on command prompt, it shows Java version 1.4.2_03 but when I tried to install new java version from java.com it says that I'm having recommended Java 7 version.

答

将 PATH 设置的内容复制到记事本并检查 1.4.2 的位置是否在 7 的位置之前.如果是，请删除路径到 PATH 设置中的 1.4.2 并保存.

Copy the contents of the PATH settings to a notepad and check if the location for the 1.4.2 comes before that of the 7. If so, remove the path to 1.4.2 in the PATH setting and save it.

保存并应用环境变量"后，关闭并重新打开 cmd 行.在 XP 中，路径不会反映在已经运行的程序中.

After saving and applying "Environment Variables" close and reopen the cmd line. In XP the path does no get reflected in already running programs.

线程“main"中的异常java.lang.UnsupportedClassVersionError: a (Unsupported major.minor version 51.0)

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