Question

I am trying to use Notepad++ as my all-in-one tool edit, run, compile, etc.

I have JRE installed, and I have setup my path variable to the .../bin directory.

When I run my “Hello world” in Notepad++, I get this message:

java.lang.UnsupportedClassVersionError: test_hello_world :
 Unsupported major.minor version 51.0
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClassCond(Unknown Source)
       .........................................

I think the problem here is about versions; some versions of Java may be old or too new.

1. How do I fix it?
2. Should I install the JDK, and setup my path variable to the JDK instead of JRE?
3. What is the difference between the PATH variable in JRE or JDK?

Answer 1

The version number shown describes the version of the JRE the class file is compatible with.

The reported major numbers are:

Java SE 22 = 66,
Java SE 21 = 65,
Java SE 20 = 64,
Java SE 19 = 63,
Java SE 18 = 62,
Java SE 17 = 61,
Java SE 16 = 60, 
Java SE 15 = 59,
Java SE 14 = 58,
Java SE 13 = 57,
Java SE 12 = 56,
Java SE 11 = 55,
Java SE 10 = 54,
Java SE 9 = 53,
Java SE 8 = 52,
Java SE 7 = 51,
Java SE 6.0 = 50,
Java SE 5.0 = 49,
JDK 1.4 = 48,
JDK 1.3 = 47,
JDK 1.2 = 46,
JDK 1.1 = 45

(Source: Wikipedia)

To fix the actual problem you should try to either run the Java code with a newer version of Java JRE or specify the target parameter to the Java compiler to instruct the compiler to create code compatible with earlier Java versions.

For example, in order to generate class files compatible with Java 1.4, use the following command line:

javac -target 1.4 HelloWorld.java

With newer versions of the Java compiler you are likely to get a warning about the bootstrap class path not being set. More information about this error is available in a blog post New javac warning for setting an older source without bootclasspath.