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I have a based class within my Java application. I would like to add new classes on the fly based on my based class. Is there any way to do it while running the application.
For example in my program, I have
class BasedClass {
private String name;
BasedClass(String name){ this.name = name;}
}
Thanks for any opinion to achieve this.
If I understand the question correct, one way to do this can be by extending the BaseClass into an abstract class and dynamically creating the abstract class' implementation / instance.
eg :
public abstract class ExtendedAbstract extends BaseClass {
public abstract void abstractMethod();
}
And...
//create dynamically anywhere in your code.
ExtendedAbstract dynClass = new ExtendedAbstract(){
public void abstractMethod(){
//implementation
...
...
}
};
.. well if this is what you want.
If this could be done at all, then how would the already running code be able to use the new classes and invoke their methods ?
I am using the base class to call the corresponding method or use the reflective tool to do it.
Ideally, I would like to be able to construct a class into a string and have some kind of Java object that will compile the class into byte stream. Once the class is in ByteCode I can then use classloader to load it in and run it.
AhHaHaHa!!! I found out how to do it. This question was so inspirational that I had to find a solution, and here it is:
A simple class to test extensions:Code://file: RealTimeClassCreation.java
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLClassLoader;
/*
* ClassCreationMain.java
*
* Created on July 27, 2005, 6:49 PM
*/
/**
* @author Zodoz
*/
public class ClassCreationMain {
BufferedWriter out;
public ClassCreationMain() throws Exception {
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What do you want to say?");
String sayWhat = in.readLine();
//create the source file
File f = new File ("SayClass.java");
out = new BufferedWriter(new FileWriter(f));
write("public class SayClass extends TestSay {");
write("\tpublic String getText() {");
write("\t\treturn \""+sayWhat+"\";");
write("\t}");
write("}");
out.close();
/*****************************
*java source file is created
*****************************/
File f2 = new File ("");
URL url = new URL("file:"+f2.getAbsolutePath()+"\\");
URLClassLoader loader = new URLClassLoader(new URL[] { url }); //url is location
//that the classes can be found
Process p = Runtime.getRuntime().exec("javac -classpath build/classes SayClass.java"); //make sure your system path is setup to run javac
/*******************************************
* use if you want to see any errors:
*
* BufferedReader pIn = new BufferedReader(new InputStreamReader(p.getErrorStream()));
* String line = "";
* while((line = pIn.readLine())!=null)
* System.out.println(line);
***********************************/
p.waitFor(); //wait to finish the process, this line is a must
Class c = loader.loadClass("SayClass"); //load the class
Object o = c.newInstance(); //create an instance of that class
TestSay ts = (TestSay)o; //typecast it to the real class that it is
System.out.println(ts.getText()); //use it
}
public void write(String write) throws Exception {
out.write(write);
out.newLine();
out.flush();
}
public static void main(String args[]) throws Exception {
new ClassCreationMain();
}
}
Please tell me if this works for you, and please fell free to ask any questions.Code:/*
* TestSay.java
*
* Created on July 27, 2005, 8:23 PM
*/
/**
*
* @author Zodoz
*/
public abstract class TestSay {
public abstract String getText();
}
