@053f521c sometimes you only need the runtime (JRE), and not the development kit. If you know an app was built with one version of the JDK, then you have to use that same version of the JRE. Most of the time Java is backwards compatible, but it is best to use the same version of the runtime the development kit was used. 

 @00e87a18 Oh okay, mm to me that seems so obvious but I suppose many wouldn't think of that.