Java Hotswapping example

gistfile1.java

/** Message.java **/

public interface Message {
    
    public void sayIt();

}

/** HelloWorld.java **/

public class HelloWorld implements Message {
    
    public void sayIt() {
        System.out.println("Hello World");
    }
}

/** HelloHotswap.java **/

public class HelloHotswap implements Message {
    
    public void sayIt() {
        System.out.println("Hello Hotswap");
    }
}

/** Main.java **/

public class main {

    public static void main(String[] args) {
        String basepath = args[0];
        Example example = new Example(basepath);
        String line = "";
        while(true) {
            try {
                java.io.BufferedReader stdin = new java.io.BufferedReader(new java.io.InputStreamReader(System.in));
                line = stdin.readLine();
            }
            catch (java.io.IOException e) { System.out.println(e); }
            catch (NumberFormatException e) { System.out.println(e); }
            
            if(line.equals("speak")) {
                example.speak();
            } else if(line.equals("exit")) {
                System.exit(0);
            } else {
                example.changeImpl(line);
            }
        }
    }

}

/** Example.java **/

import org.codemonkey.javareflection.ExternalClassLoader;

public class Example {

    Class impl;
    ExternalClassLoader loader;

    public Example(String basepath) {
        loader = new ExternalClassLoader();
        loader.setBasepath(basepath);
    }

    public void changeImpl(String path) {
        try {
            impl = loader.loadClass(path);
        } catch(ClassNotFoundException e) {
            System.err.println("Class not found");
        } catch(Exception e) {
            System.err.println("Something went wrong");
        }
    }

    public void speak() {
        try {
            Message instance = (Message)impl.newInstance();
            instance.sayIt();
        } catch(Exception e) {
            System.err.println("Reflection error");
        }
    }

}