JAVA - get class from file.java located on disk

Question

I want to load class definition or fields from file.java located on disk. I tried URLClassLoader:

        URL url = file.toURL();
        URL[] urls = new URL[]{url};
        ClassLoader cl = new URLClassLoader(urls);
        Class c = new Object().getClass();
        try {
            c = cl.loadClass(className);
        } catch (ClassNotFoundException e1) {
              System.err.println("not found class: " + className);
        }

But it doesnt work ;(

Answer 1

You can load classes via loadClass , but not source code files. .java files contain source code . With Java, as with many (but not all) other languages, you must "compile" the source code into a machine-readable form — in the case of Java, a .class file (which may or may not then be bundled into a .jar ). You compile Java code with the javac tool (or the features of your IDE).

For instance, if you have a class called Foo defined in a file called Foo.java , then:

javac Foo.java

...will create Foo.class , which can then be loaded.

You may find this "Getting Started": The "Hello World" application tutorial from Oracle useful. It goes through the steps of getting the tools set up on your computer, writing a source file, compiling it into a class file, and running it.