Is it possible to have a uniform exception handler for all instance methods of a class in Java? For example, if I have the class Car:
class Car {
public void drive(double miles) {
...
}
public void turnLeft() {
...
}
public void turnRight() {
...
}
}
Could I add a handler function that is called every time an exception is thrown by one of these methods? The ultimate goal would be to log all of these exceptions in a uniform way, even if they are ultimately caught and ignored by higher levels of the stack.
Extend a Proxy to delegate Car. We can use jdk Proxy if car has a interface, or use cglib. Just like what some framework(Spring...) has provided.
Code below is a example of cglib.
class ErrorHandleProxy implements MethodInterceptor {
public Object createProxy(Object target) {
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(target.getClass());
enhancer.setCallback(this);
enhancer.setClassLoader(target.getClass().getClassLoader());
return enhancer.create();
}
#Override
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
Object ret = null;
try {
ret = proxy.invokeSuper(obj, args);
} catch (Exception e) {
/// do logging or rethrow exception
}
return ret;
}
}
And then, we can call car with this Proxy
Car car = new Car();
Car proxy = (Car)new ErrorHandleProxy().createProxy(car);
proxy.xxx
If you are using spring , then you can catch all exceptions in one class https://www.baeldung.com/exception-handling-for-rest-with-spring Using an ExceptionMapper class.
If it is a normal app, in your public static void main you can surround your code in try catch to catch all exceptions.
I want to have a class to run other classes in java, like constructor parameterized with a class to run that class later on, similar to this
class MyClass{
Class classToRun;
public MyClass(Class c) {
super();
this.classToRun = c;
}
public void runClass(){
classToRun.someStaticMethod();
}
}
where classToRun possible classes doesn't have a common ancestor, but all have method someStaticMethod, and have no idea about MyClass, which runs them.
But there are problems, like inner classes cannot have static methods, classes cannot be cast Class, etc.
There are solutions for parameterized with class methods, like
How do I pass a class as a parameter in Java?
Passing a class as an argument to a method in java
but not for constructors.
What is the proper solution to do this?
Use lambdas and pass the method reference: they match on the method signature. For void someStaticMethod() you can use Runnable.
class MyClass{
private final Runnable methodToRun;
public MyClass(Runnable someStaticMethod) {
methodToRun = someStaticMethod;
}
public void runClass(){
methodToRun.run();
}
}
new MyClass(SomeClass::someStaticMethod).runClass();
You cannot enforce that the method passed has the right name, but looks even neater IMHO.
You need to understand what generics are.
interface
public interface SomeInterface {
void someStaticMethod();
}
use
class MyClass<T extends SomeInterface>{
T classToRun;
public MyClass(T c) {
super();
this.classToRun = c;
}
public void runClass(){
classToRun.someStaticMethod();
}
}
As 2 of 3 answers were not to the point, I decided to publish fixed versions of both answers as far as they can be fixed.
The f1sh version from the above should like follows:
public class ClassToRunOthers {
Class classToRun;
public ClassToRunOthers(Class c) {
this.classToRun = c;
}
public void runClass() throws Exception {
Optional<Method> method = Arrays.stream(classToRun.getDeclaredMethods()).filter(m -> m.getName().equals("someStaticMethod")).findFirst();
if(!method.isPresent()) {
throw new RuntimeException();
}
method.get().invoke(null);
}
public static void main(String[] args) throws Exception {
ClassToRunOthers mc = new ClassToRunOthers(SomeClass.class);
mc.runClass();
}
}
class SomeClass {
static void someStaticMethod() {
System.out.println("test");
}
}
The zwei solution above can not be fixed without reflection, as generics is not to the point. Evan if you try to parametrize not with SomeInerface (because SomeClass does not extend a common SomeInterface), but with Object, it is still won't solve the problem:
public class MyClass<T extends Object> {
T classToRun;
public MyClass(T c) {
super();
this.classToRun = c;
}
public void runClass() {
// classToRun.someStaticMethod(); // Cannot resolve method 'someStaticMethod' in 'T'
}
public static void main(String[] args) {
MyClass mc = new MyClass(SomeClass.class);
}
}
class SomeClass {
static void someStaticMethod() {
System.out.println("test");
}
}
This can be fixed like the above, via reflection.
I believe, it can be done with annotations in some elegant way, and may be someone will share us with such a solution or I will do it by myself as time permits.
By now for myself, a solution with saving class name in the String in constructor next day after the question been asked did the trick.
You will have to use reflection if you want to execute a method when you only have the Class instance.
In the code below, runClass finds the method of the class using it's name as a String, then executes it. This code assumes that the method is static, also ignoring any Exception handling.
The following code prints "test":
class MyClass {
Class classToRun;
public MyClass(Class c) {
this.classToRun = c;
}
public void runClass() throws Exception {
Optional<Method> method = Arrays.stream(classToRun.getDeclaredMethods()).filter(m -> m.getName().equals("someStaticMethod")).findFirst();
if(!method.isPresent()) {
throw new RuntimeException();
}
method.get().invoke(null);
}
}
class Main {
public static void main(String[] args) throws Exception {
MyClass mc = new MyClass(Main.class);
mc.runClass();
}
static void someStaticMethod() {
System.out.println("test");
}
}
In Java, I'm trying to override a class coming from a library. One of the constructors of the class is private and thus I'm not able to call it from my class. Is there a way to work around this (reflection?)?
public class LibraryClass extends ProtectedLibraryClass {
public LibraryClass() {
super();
}
private LibraryClass(Boolean useFeature) {
super(useFeature);
}
// Other methods
}
public class MyClass extends LibraryClass {
public MyClass() {
super();
}
private MyClass(Boolean useFeature) {
super(useFeature); // <-- This line throws exception as super class constructor is private
}
// Override other methods
}
I can't just call super() and then set useFeature flag as useFeature flag is final in protectedLibraryClass and is set only through it's constructor.
they made it for a reason but you can use reflection in java to create object from this class even if it private
here is example :
public static void main(String[] args) {
LibraryClass copy = null;
try {
Constructor[] constructors = LibraryClass.class.getDeclaredConstructors();
for (Constructor constructor : constructors) {
constructor.setAccessible(true);
copy = (LibraryClass) constructor.newInstance();
break;
}
} catch (Exception e) {
e.printStackTrace();
}
}
I don't think this is possible, looking at this post and these docs. What you could possibly do is place the two (or however many) class files into their own package and then use the protected access modifier so that the constructor is only usable within the package. If you only place classes that inherit from the LibraryClass class it would have the same effect as making the constructor private as indicated above.
Say I have a class with many of public methods:
public class MyClass {
public void method1() {}
public void method2() {}
(...)
public void methodN() {}
}
Now I would like to create a wrapper class which would delegate all the methods to wrapped instance (delegate):
public class WrapperClass extends MyClass {
private final MyClass delegate;
public WrapperClass(MyClass delegate) {
this.delagate = delegate;
}
public void method1() { delegate.method1(); }
public void method2() { delegate.method2(); }
(...)
public void methodN() { delegate.methodN(); }
}
Now if MyClass has a lot of methods I would need to override each of them which is more or less the same code which just "delegates". I was wondering if it is possible to do some magic to automatically call a method in Java (so the Wrapper class would need to say "Hey if you call a method on me just go to delegate object and call this method on it).
BTW: I can not use inheritance because the delegate is not under my control.I just get its instance from elsewhere (another case would be if MyClass was final).
NOTE: I do not want IDE generation. I know I can do it with help of IntelliJ/Eclipse, but I'm curious if this can be done in code.
Any suggestions how to achieve something like this? (NOTE: I would probably be able to do it in some scripting languages like php where I could use php magic functions to intercept the call).
Perhaps the dynamic Proxy of java can help you. It only works if you consequently use interfaces. In this case, I will call the interface MyInterface and set up a default implementation:
public class MyClass implements MyInterface {
#Override
public void method1() {
System.out.println("foo1");
}
#Override
public void method2() {
System.out.println("foo2");
}
#Override
public void methodN() {
System.out.println("fooN");
}
public static void main(String[] args) {
MyClass wrapped = new MyClass();
wrapped.method1();
wrapped.method2();
MyInterface wrapper = WrapperClass.wrap(wrapped);
wrapper.method1();
wrapper.method2();
}
}
The wrapper class implementation would look like:
public class WrapperClass extends MyClass implements MyInterface, InvocationHandler {
private final MyClass delegate;
public WrapperClass(MyClass delegate) {
this.delegate = delegate;
}
public static MyInterface wrap(MyClass wrapped) {
return (MyInterface) Proxy.newProxyInstance(MyClass.class.getClassLoader(), new Class[] { MyInterface.class }, new WrapperClass(wrapped));
}
//you may skip this definition, it is only for demonstration
public void method1() {
System.out.println("bar");
}
#Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Method m = findMethod(this.getClass(), method);
if (m != null) {
return m.invoke(this, args);
}
m = findMethod(delegate.getClass(), method);
if (m != null) {
return m.invoke(delegate, args);
}
return null;
}
private Method findMethod(Class<?> clazz, Method method) throws Throwable {
try {
return clazz.getDeclaredMethod(method.getName(), method.getParameterTypes());
} catch (NoSuchMethodException e) {
return null;
}
}
}
Note that this class:
extends MyClass, to inherit a default implementation (any other would do)
implements Invocationhandler, to allow the proxy to do reflection
optionally implement MyInterface (to satisfy the decorator pattern)
This solution allows you to override special methods, but to delegate all others. This will even work with sub classes of Wrapper class.
Note that the method findMethod does not yet capture the special cases.
This question is 6 months old already and #CoronA's wonderful answer has satisfied and been accepted by #walkeros, but I thought I would add something here as I think this can be pushed an extra step.
As discussed with #CoronA in the comments to his answer, instead of having to create and maintain a long list of MyClass methods in WrapperClass (i.e. public void methodN() { delegate.methodN(); }), the dynamic proxy solution moves this to the interface. The issue is that you still have to create and maintain a long list of signatures for the MyClass methods in the interface, which is perhaps a bit simpler but doesn't completely solve the problem. This is especially the case if you don't have access to MyClass in order to know all the methods.
According to Three approaches for decorating your code,
For longer classes, a programmer must choose the lesser of two evils:
implement many wrapper methods and keep the type of decorated object
or maintain a simple decorator implementation and sacrifice retaining
the decorated object type.
So perhaps this is an expected limitation of the Decorator Pattern.
#Mark-Bramnik, however, gives an fascinating solution using CGLIB at Interposing on Java Class Methods (without interfaces). I was able to combine this with #CoronaA's solution in order to create a wrapper that can override individual methods but then pass everything else to the wrapped object without requiring an interface.
Here is MyClass.
public class MyClass {
public void method1() { System.out.println("This is method 1 - " + this); }
public void method2() { System.out.println("This is method 2 - " + this); }
public void method3() { System.out.println("This is method 3 - " + this); }
public void methodN() { System.out.println("This is method N - " + this); }
}
Here is WrapperClass which only overrides method2(). As you'll see below, the non-overridden methods are, in fact, not passed to the delegate, which can be a problem.
public class WrapperClass extends MyClass {
private MyClass delagate;
public WrapperClass(MyClass delegate) { this.delagate = delegate; }
#Override
public void method2() {
System.out.println("This is overridden method 2 - " + delagate);
}
}
Here is MyInterceptor which extends MyClass. It employs the proxy solution using CGLIB as described by #Mark-Bramnik. It also employs #CononA's method of determining whether or not to send the method to the wrapper (if it is overridden) or the wrapped object (if it is not).
import java.lang.reflect.Method;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
public class MyInterceptor extends MyClass implements MethodInterceptor {
private Object realObj;
public MyInterceptor(Object obj) { this.realObj = obj; }
#Override
public void method2() {
System.out.println("This is overridden method 2 - " + realObj);
}
#Override
public Object intercept(Object arg0, Method method, Object[] objects,
MethodProxy methodProxy) throws Throwable {
Method m = findMethod(this.getClass(), method);
if (m != null) { return m.invoke(this, objects); }
Object res = method.invoke(realObj, objects);
return res;
}
private Method findMethod(Class<?> clazz, Method method) throws Throwable {
try {
return clazz.getDeclaredMethod(method.getName(), method.getParameterTypes());
} catch (NoSuchMethodException e) {
return null;
}
}
}
Here is Main and the results you get if you run it.
import net.sf.cglib.proxy.Enhancer;
public class Main {
private static MyClass unwrapped;
private static WrapperClass wrapped;
private static MyClass proxified;
public static void main(String[] args) {
unwrapped = new MyClass();
System.out.println(">>> Methods from the unwrapped object:");
unwrapped.method1();
unwrapped.method2();
unwrapped.method3();
wrapped = new WrapperClass(unwrapped);
System.out.println(">>> Methods from the wrapped object:");
wrapped.method1();
wrapped.method2();
wrapped.method3();
proxified = createProxy(unwrapped);
System.out.println(">>> Methods from the proxy object:");
proxified.method1();
proxified.method2();
proxified.method3();
}
#SuppressWarnings("unchecked")
public static <T> T createProxy(T obj) {
Enhancer e = new Enhancer();
e.setSuperclass(obj.getClass());
e.setCallback(new MyInterceptor(obj));
T proxifiedObj = (T) e.create();
return proxifiedObj;
}
}
>>> Methods from the unwrapped object:
This is method 1 - MyClass#e26db62
This is method 2 - MyClass#e26db62
This is method 3 - MyClass#e26db62
>>> Methods from the wrapped object:
This is method 1 - WrapperClass#7b7035c6
This is overridden method 2 - MyClass#e26db62
This is method 3 - WrapperClass#7b7035c6
>>> Methods from the proxy object:
This is method 1 - MyClass#e26db62
This is overridden method 2 - MyClass#e26db62
This is method 3 - MyClass#e26db62
As you can see, when you run the methods on wrapped you get the wrapper for the methods that are not overridden (i.e. method1() and method3()). When you run the methods on proxified, however, all of the methods are run on the wrapped object without the pain of having to delegate them all in WrapperClass or put all of the method signatures in an interface. Thanks to #CoronA and #Mark-Bramnik for what seems like a pretty cool solution to this problem.
Check the #Delegate annotation from Lombok framework:
https://projectlombok.org/features/Delegate.html
Switch to Groovy :-)
#CompileStatic
public class WrapperClass extends MyClass {
#Delegate private final MyClass delegate;
public WrapperClass(MyClass delegate) {
this.delagate = delegate;
}
//Done. That's it.
}
http://mrhaki.blogspot.com/2009/08/groovy-goodness-delegate-to-simplify.html
You don't have to do this -- your Wrapper class is a subclass of the original class, so it inherits all of its publicly accessible methods -- and if you don't implement them, the original method will be called.
You shouldn't have extends Myclass together with a private MyClass object -- that's really really redundant, and I can't think of a design pattern where doing that is right. Your WrapperClass is a MyClass, and hence you can just use its own fields and methods instead of calling delegate.
EDIT: In the case of MyClass being final, you'd be circumventing the willfull declaration to not allow subclassing by "faking" inheritance; I can't think of anyone willing to do that other than you, who is in control of WrapperClass; but, since you're in control of WrapperClass, not wrapping everything you don't need is really more than an option -- it's the right thing to do, because your object is not a MyClass, and should only behave like one in the cases you mentally considered.
EDIT you've just changed your question to mean something completely different by removing the MyClass superclass to your WrapperClass; that's a bit bad, because it invalidates all answers given so far. You should have opened another question.
Credits go to CoronA for Pointing out the Proxy and InvocationHandler classes. I worked out a more reusable utility class based on his solution, using generics:
public class DelegationUtils {
public static <I> I wrap(Class<I> iface, I wrapped) {
return wrapInternally(iface, wrapped, new SimpleDecorator(wrapped));
}
private static <I> I wrapInternally (Class<I> iface, I wrapped, InvocationHandler handler) {
return (I) Proxy.newProxyInstance(wrapped.getClass().getClassLoader(), new Class[] { iface }, handler);
}
private static class SimpleDecorator<T> implements InvocationHandler {
private final T delegate;
private SimpleDecorator(T delegate) {
this.delegate = delegate;
}
#Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Method m = findMethod(delegate.getClass(), method);
if (m == null) {
throw new NullPointerException("Found no method " + method + " in delegate: " + delegate);
}
return m.invoke(delegate, args);
}
}
private static Method findMethod(Class<?> clazz, Method method) throws Throwable {
try {
return clazz.getDeclaredMethod(method.getName(), method.getParameterTypes());
} catch (NoSuchMethodException e) {
return null;
}
}
}
Test it:
public class Test {
public interface Test {
public void sayHello ();
}
public static class TestImpl implements Test {
#Override
public void sayHello() {
System.out.println("HELLO!");
}
}
public static void main(String[] args) {
Test proxy = DelegationUtils.wrap(Test.class, new TestImpl());
proxy.sayHello();
}
}
I wanted to create an automatic delegation class that executes the delegatee's methods on the EDT. With this class, you just create a new utility method that will use an EDTDecorator, in which the implementation will wrap m.invoke in a SwingUtilities.invokeLater.
However, if I reflect on this, I may want to reconsider making a non-Reflection based proxy per interface that I have - it might be cleaner and faster, and more understandable. But, it's possible.
Define a method in WrapperClass i.e. delegate() that returns the instance of MyClass
OR
You can use reflection to do that but the caller has to pass the method name as an argument to an exposed method. And there will be complications regarding the method arguments/overloaded methods etc.
BTW: I can not use inheritance because the delegate is not under my control.I just get its instance from elsewhere (another case would be if MyClass was final)
The code that you have posted has public class WrapperClass extends MyClass
Actually your current implementation of WrapperClass is actually a decorator on top of MyClass
Let me redefine the problem for a specific case.
I want to override the close method of ResultSet interface in jdbc. My aim is to close the preparedstatement in close method of result set. I could not access to the Class (DelegatingResultSet) that implements in ResultSet interface. There are a lot of methods in ResultSet interface and overriding them one by one and calling the corresponding method from the ResultSet object is one solution. For a dynamic solution I used Dynamic ProxyClasses (https://docs.oracle.com/javase/1.5.0/docs/guide/reflection/proxy.html).
// New ResultSet implementation
public class MyResultSet implements InvocationHandler {
ResultSet rs;
PreparedStatement ps;
private Method closeMethod;
public MyResultSet(ResultSet rs, PreparedStatement ps) {
super();
this.rs = rs;
this.ps = ps;
try {
closeMethod = ResultSet.class.getMethod("close",null);
} catch (NoSuchMethodException | SecurityException e) {
e.printStackTrace();
}
}
public void close() {
try {
rs.close();
ps.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
public static Object newInstance(ResultSet rs, PreparedStatement ps) {
return java.lang.reflect.Proxy.newProxyInstance(rs.getClass().getClassLoader(), rs.getClass().getInterfaces(),
new MyResultSet(rs,ps));
}
public Object invoke(Object proxy, Method m, Object[] args)
throws Throwable {
Object result = null;
try {
Class declaringClass = m.getDeclaringClass();
if (m.getName().compareTo("close")==0) {
close();
} else {
result = m.invoke(rs, args);
}
} catch (InvocationTargetException e) {
throw e.getTargetException();
} catch (Exception e) {
throw new RuntimeException(e.getMessage());
} finally {
}
return result;
}
}
// How to call it:
ResultSet prs = (ResultSet) MyResultSet.newInstance(rs,ps);
I really appreciated #CoronA's answer. I also looked at #Mark Cramer's answer, but, if I'm not missing something, I think that there are always at least two instances of the "proxified" class with a strange relationship beteen the two objects.
This, along with the fact that cglib is now deprecated, pushed me to find a new implementation based on ByteBuddy.
This is what I came up with:
public class MyClass {
public String testMethod() {
return "11111";
}
public String testMethod2() {
return "aaaaa";
}
}
public class MyClassWithDelegate extends MyClass {
private static final Constructor<? extends MyClassWithDelegate> CONSTRUCTOR_WITH_DELEGATE;
static {
Constructor<? extends MyClassWithDelegate> temp = null;
try {
final var instrumentedMyClassWithDelegateType =
new ByteBuddy()
.subclass(MyClassWithDelegate.class)
.method(ElementMatchers.any())
.intercept(MethodDelegation.to(MethodInterceptor.class))
.make()
.load(MyClassWithDelegate.class.getClassLoader())
.getLoaded();
temp = instrumentedMyClassWithDelegateType.getConstructor(MyClass.class);
} catch (final Exception e) {
LOGGER.error("Cannot instrument class {}", MyClassWithDelegate.class, e);
}
CONSTRUCTOR_WITH_DELEGATE = temp;
}
public static MyClassWithDelegate getInstanceWithDelegate(final MyClass myClass) {
try {
return CONSTRUCTOR_WITH_DELEGATE.newInstance(myClass);
} catch (final Exception e) {
LOGGER.error("Cannot get instance of {}", MyClassWithDelegate.class, e);
throw new IllegalStateException();
}
}
private final boolean initialized;
private final MyClass delegate;
public MyClassWithDelegate(final MyClass delegate) {
super();
this.delegate = delegate;
this.initialized = true;
}
public String testMethod() {
return "22222";
}
public static class MethodInterceptor {
#RuntimeType
public static Object intercept(#This final MyClassWithDelegate self,
#Origin final Method method,
#AllArguments final Object[] args,
#SuperMethod final Method superMethod) throws Throwable {
if (!self.initialized || method.getDeclaringClass().equals(MyClassWithDelegate.class)) {
return superMethod.invoke(self, args);
} else {
return method.invoke(self.delegate, args);
}
}
}
}
The initialized field is used to prevent method calls the super constructor from being redirected to the delegate before its assignment (in this case it wouldn't be a problem, but I wanted to create a generic solution).
Every method called on an instance of MyClassWithDelegate will be redirected to the delegate, except from methods declared inside MyClassWithDelegate itself.
In this example, calling testMethod() on an instance of MyClassWithDelegate will return "22222", while testMethod2() will return "aaaaa".
Obviously, the delegation will actually work only if every instance of MyClassWithDelegate is obtained calling the getInstanceWithDelegate factory method.
I have a super class A, and classes B, C and D that extend A.
class A {}
class B extends A {}
class C extends A {}
class D extends A {}
Then I have a list like this:
[B.class, C.class, D.class]
I take a random item from the list and instantiate it like so:
Object obj = list.get(i).newInstance()
Now I need to pass obj to a method that accepts objects of type A as a parameter.
A a = (A) obj
causes java to throw an exception (Either InstantiationException or IllegalAccessException, I don't know because android studio won't stop at breakpoints inside the catch, and any attempt to save information about the exception from the catch results in null...).
I understand why I can't dynamically specify the new object type and then cast obj to that type, but if they all share the common parent, I don't see why it wouldn't work.
Can anybody enlighten me how to fix what I'm currently doing, or achieve the same thing in a similar way?
Thanks! /Max
The newInstance method can throw an InstantiationException or IllegalAccessException, hence the warning you're probably seeing in your IDE if this call isn't wrapped in a try/catch. Your simple example seems to work fine though.
class A {}
class B extends A {}
class C extends A {}
public class Test {
public static void main(String[] args) throws Exception {
List<Class> list = new LinkedList<Class>();
list.add(B.class);
list.add(C.class);
Object obj = list.get(0).newInstance();
A a = (A) obj;
System.out.println(a instanceof B);
}
}
Prints "true"
In the end this was due to a bug with android studio. Rewriting the code fixed the problem and I wasn't able to reproduce this issue
Other symptoms that future searchers might find useful:
android studio would not stop at breakpoints inside a catch block
Any attempt to save information about the exception inside the catch resulted in null (see example below)
:
Exception ex = null;
try {
// do something that raises an exception
ex = new Exception();
} catch (Exception ex) {
ex = ex;
}
// ex == null
As pointed out by the other answers, what I was describing in my question does not normally raise an exception.
The code seems to be working absolutely fine. I am not understanding your question.
package testplayground;
import java.util.ArrayList;
import java.util.List;
class A {
void print() {
System.out.println("inside A");
}
}
class B extends A {
public void print() {
System.out.println("inside B");
}
}
class C extends A {
public void print() {
System.out.println("inside C");
}
}
class D extends A {
public void print() {
System.out.println("inside D");
}
}
public class TestPlayGround {
public static void main(String[] args) {
try {
List<Class> list = new ArrayList<Class>();
list.add(B.class);
list.add(C.class);
list.add(D.class);
for (Class classObj : list) {
Object obj = classObj.newInstance();
A a = (A) obj;
methodA(a);
}
} catch (Exception e) {
e.printStackTrace();
}
}
private static void methodA(A a) {
a.print();
}
}
output:-
inside B
inside C
inside D