title: Java / Eclipse : switching from JRE .6 to .7
body: <p>I have the JRE 1.6 and 1.7 installed (as well as the JDK) in c:/program files/java/</p>
  
  <p>I first had 1.7 installed then installed 1.6 as well.
  I am using Eclipse as my IDE -please note I am new to Java.</p>
  
  <p>When I want to switch to 1.6 I go to "Run configurations" (in Eclipse) and select alternative JREs, pick 1.6 and click apply. But when I try to run a simple HelloWorld program I get this alert:</p>
  
  <blockquote>
    <p>Could not find the main class:HelloW. Program will exit.</p>
  </blockquote>
  
  <p>And in the console I get these errors:</p>
  
  <pre><code>java.lang.UnsupportedClassVersionError: HelloW : Unsupported major.minor version 51.0
      at java.lang.ClassLoader.defineClass1(Native Method)
      at java.lang.ClassLoader.defineClassCond(Unknown Source)
      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$000(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)
  </code></pre>
  
  <p>If I switch back to JRE 1.7 everything works again.
  How can I properly switch to 1.6 and get everything working?</p>