Interface - AbstractClass Collision

[Azrael Noor]

package demoprograms;

interface InterfacesDemo1
{
    void display();
}

abstract class azrael
{
    private abstract void display();
}

interface burjAlHaq
{
    void display();
}

public class InterfacesDemo extends azrael implements InterfacesDemo1,burjAlHaq
{
    public static void main(String[] args)
    {
        InterfacesDemo idm = new InterfacesDemo();
        idm.display();
    }

    public void display()
    {
        System.out.println("Yahoo");
    }

    @Override
    private void display() {
        System.out.println("Vahoo");
    }
}

java.lang.ClassFormatError: Method display in class demoprograms/azrael  has illegal modifiers: 0x402
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
        at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
        at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: demoprograms.InterfacesDemo.  Program will exit.

Why am i getting error in above code? Please if somebody can explain underlying reason for it?

[Maneesh Godbole]

Because abstract and private are like oil and water. They do not mix

[Rob Spoor]

Maneesh is right. Abstract means the method is meant to be overridden, but private methods cannot be overridden (only shadowed).

[Azrael Noor]

Thank You for reply

but what about following case as there is default in class and public in interfaces and it is working fine why so? as methods are abstract both sides?

interface InterfacesDemo1
{
    void display();
}

abstract class azrael
{
   abstract void display();
}

interface alHaq
{
    void display();
}

public class InterfacesDemo extends azrael implements InterfacesDemo1,alHaq
{
    public static void main(String[] args)
    {
        InterfacesDemo idm = new InterfacesDemo();
        idm.display();
    }

    @Override
    public void display() {
        throw new UnsupportedOperationException("Not supported yet.");
    }
}

[Matthew Brown]

If a method is overridable at all, you can always override it with fewer restrictions. So overriding package or protected methods with public is fine.

[Jesper de Jong]

The error that you are getting looks really strange.

java.lang.ClassFormatError: Method display in class demoprograms/azrael has illegal modifiers: 0x402

It indicates that the class file is invalid. Somehow the compiler that you are using has accepted illegal code (a method that is both abstract and private) without giving an error message, and produced an invalid class file. That's a bug in the compiler.

Which compiler are you using? Is this the standard javac from the JDK (if so, what version)?

[Azrael Noor]

Thank you for providing information

I am Using JDK version 6, JAVAC

what other compilers are available which compile Java Code?

[Campbell Ritchie]

Where did you get that compiler from?

[Azrael Noor]

From Oracle Website

[Campbell Ritchie]

I am very surprised it would allow those two modifiers together. Maybe the class was compiled with a different compiler, or (even) it has been altered after compilation. Or there was an error in transmission or recording of the .class file.

[Azrael Noor]

BUG IN JAVA BUG IN JAVA

but i need to continue the program

[Campbell Ritchie]

Azrael Noor wrote:BUG IN JAVA BUG IN JAVA

I suggest you try compiling that class again, with the same version of the compiler, before you try to report a bug