Cross compiling in java .... :P

Cross compilation in java:

Basics: 

Here I have two JDK locations in my system.

1) Default Jdk (1.6) is located in $JAVA_HOME (/usr/lib/jdk1.6.0_45)

2) Lower version Jdk (1.5) is located in ~/jdk_5/jdk1.5.0_22/ 

Now take a sample class 

public class Test{

            public static void main(String nag[]){

                     

                     System.out.println("Hello Nagarjuna");

            }

}//end class

now I am compiling using jdk 1.6 like

                $ $JAVA_HOME/bin/javac Test.java

It will be compile and generate Test.class

And now try to run this Test.class file using jdk 1.6

                $ $JAVA_HOME/bin/java Test

                o/p :  Hello Nagarjuna

lly, Now try to run with  jdk 1.5

           $ ~/jdk_5/jdk1.5.0_22/bin/java Test

         o/p:  

       Exception in thread "main" java.lang.UnsupportedClassVersionError: Bad version number in .class file

at java.lang.ClassLoader.defineClass1(Native Method)

at java.lang.ClassLoader.defineClass(ClassLoader.java:621)

at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)

at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)

at java.net.URLClassLoader.access$100(URLClassLoader.java:56)

at java.net.URLClassLoader$1.run(URLClassLoader.java:195)

at java.security.AccessController.doPrivileged(Native Method)

at java.net.URLClassLoader.findClass(URLClassLoader.java:188)

at java.lang.ClassLoader.loadClass(ClassLoader.java:307)

at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:268)

at java.lang.ClassLoader.loadClass(ClassLoader.java:252)

at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)

It is because of higher version compilation and lower version execution.

           But we can compile the above Test.java using jdk 1.5 and can run the generated Test.class file in both jdk1.6 and jdk1.5 . Because lower version compilation can support higher (Latest) version execution.

Now, let us try cross compilation in jdk 1.6

Cross compilation:  

Here we use javac arguments  ( only 'target')

Use 'taget' argument to javac while compiling with jdk1.6.

compilation: 

$ $JAVA_HOME/bin/javac -target 1.5 Test.java

And now, Let us try to run the generated Test.class file in both jdk 1.6 and jdk 1.5

first in jdk 1.6 -

          $ $JAVA_HOME/bin/java Test

          o/p: Hello Nagarjuna

 in jdk 1.5 -

           $  ~/jdk_5/jdk1.5.0_22/bin/java Test

           o/p: Hello Nagarjuna

So, we can do cross compilation using any higher version JDK. 

Try on your own