I have the real object and dynamic proxy handler classes, for dynamic proxy hanler I substitute all returned string values to some other values and return them in the implemented method, however, the values from the original return are returned and I can only modify the call arguments, not the return values.
package reflection;
public class RealObject implements Interface {
#Override
public void doSomething() {
System.out.println("Do Something");
}
#Override
public String returnSomethingElse(String arg) {
System.out.println("Do something else "+arg
);
return arg;
}
}
and here is the test and the handler:
package reflection;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
public class SimpleProxyDemo
{
public static void process(Interface iface)
{
iface.doSomething();
iface.returnSomethingElse("argsHere");
}
public static void main(String[] args) {
process(new RealObject());
//process(new SimpleProxy(new RealObject()));
//Interface dynamicProxy=(Interface) Proxy.newProxyInstance(Interface.class.getClassLoader(),new Class[]{Interface.class},new SimpleProxyDemo().new DynamicProxyHandler(new RealObject()));
Interface dynamicProxy=(Interface) Proxy.newProxyInstance(Interface.class.getClassLoader(),new Class[]{Interface.class},new DynamicProxyHandler(new RealObject()));
process(dynamicProxy);
}
static class DynamicProxyHandler implements InvocationHandler{
private Object proxied;
public DynamicProxyHandler(Object proxied)
{
this.proxied=proxied;
}
#Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("THIS IS BEFORE CALL FROM DYNAMIC PROXY, CALLING METHOD "+method.getName());
if (args!=null&&args.length>0) {
args[0] = args[0] + "I DO INFLUENCE";
}
//Object toBeReturned= method.invoke(proxied,args+"I DO INFLUENCE");
Object toBeReturned= method.invoke(proxied,args);
System.out.println("THIS IS AFTER CALL FROM DYNAMIC PROXY, CALLING METHOD "+method.getName());
//if (toBeReturned instanceof String) {
if (toBeReturned !=null) {
return "OLOLO I CAN INFLUENCE";
}
else
return toBeReturned;
}
}
}
My expectation is that for the methods that return String the returned value would be substituted by my String "OLOLO I CAN INFLUENCE", but the proxy object don't return it in its methods.
and here is the output:
Do Something
Do something else argsHere
THIS IS BEFORE CALL FROM DYNAMIC PROXY, CALLING METHOD doSomething
Do Something
THIS IS AFTER CALL FROM DYNAMIC PROXY, CALLING METHOD doSomething
THIS IS BEFORE CALL FROM DYNAMIC PROXY, CALLING METHOD returnSomethingElse
Do something else argsHereI DO INFLUENCE
THIS IS AFTER CALL FROM DYNAMIC PROXY, CALLING METHOD returnSomethingElse
so it looks like Object toBeReturned= method.invoke(proxied,args); and returning it in the end of invoke method has absolutely no influence on what the proxy returns? Uneasy to believe, so where is my mistake?
The explanation is very straightforward: if was checking not the value returned by the intercepted proxy method, but instead, was checking the call that occured inside the proxied method, so it is clear that everything works here as expected.
I want to be able to determine if a base class method has been overridden by a subclass specifically because expensive setup is needed before invoking it and most subclasses in our system do not override it. Can it be tested by using reflection provided method handles? Or is there some other way to test if a class method is overridden?
e.g.
class BaseClass {
void aMethod() { // don nothing }
protected boolean aMethodHasBeenOverridden() {
return( // determine if aMethod has been overridden by a subclass);
}
}
You can do it with reflection by examining the declaring class of your method:
class Base {
public void foo() {}
public void bar() {}
}
class Derived extends Base {
#Override
public void bar() {}
}
...
Method mfoo = Derived.class.getMethod("foo");
boolean ovrFoo = mfoo.getDeclaringClass() != Base.class;
Method mbar = Derived.class.getMethod("bar");
boolean ovrBar = mbar.getDeclaringClass() != Base.class;
System.out.println("Have override for foo: "+ovrFoo);
System.out.println("Have override for bar: "+ovrBar);
Prints
Have override for foo: false
Have override for bar: true
Demo.
This can be done calling getClass().getDeclaredMethod("aMethod"), which returns something only if the class of this declared it.
Here's an implementation of your method:
/**
* #return true if the instance's class overrode aMethod
*/
protected boolean aMethodHasBeenOverridden() {
try {
return getClass() != A.class && getClass().getDeclaredMethod("aMethod") != null;
} catch (NoSuchMethodException | SecurityException e) {
return false;
}
}
The approach I'd take is to only make this method exist if the subclass needs it by overriding method that calls it in an abstract intermediate class. Here's what that would look like:
public abstract class MovingThing {
public void move() {
// walk a few feet
}
}
Now a few of your moving things teleport, but that requires charging the flux capacitors and other expensive things, so separate that out:
public abstract class TeleportingThing extends MovingThing {
#Override
public void move() {
fluxCapacitor.charge();
stardate.calculate();
doTeleport();
}
protected abstract void doTeleport();
}
Your classes that need the expensive setup derive from the second class that includes it, while the ones that don't can derive from the first class. This pattern is a sort of Decorator and is used, for example, in the Servlet API, where most servlets override something like doGet() and leave the parsing to service().
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 am currently using EasyMock and creating mock objects like this
mockedObject = createMock(myInterface.class);
Easy mock is an unnecessary overhead(because the method that i mock is really simple) and i would like to create a mock without it.
But the problem is myInterface is an interface so how do i instantiate it.Please suggest.
Thanks,
Sriram
The easiest way would be to create an inner class that implements the interface, implement the methods to return the data that you want, then use it in the test case.
For example:
public void testMethod ( )
{
MyInterface mockObject = new MyInterface ( ) {
public void myMethod ( )
{
// NOOP
}
public int myFunction ( )
{
return -1 ;
}
}
// Proceed with the test case using mockObject
}
You can create and Anoymous class e.g.
MyInterface myMock = new MyInterface() {
... methods implemented here
};
If you need to verify the number of times a method is called you can add a simple counter member for each method.
e.g.
public void testMethod ( )
{
MyInterface mockObject = new MyInterface ( ) {
public int MyMethodCount = 0;
public int MyFunctionCount = 0;
public void myMethod ( )
{
MyMethodCount++;
// NOOP
}
public int myFunction ( )
{
MyFunctionCount++;
return -1 ;
}
}
// Proceed with the test case using mockObject
}
In the absence of a mock framework, java.lang.reflect.Proxy is your best bet. If you've never used it before, you can create a dynamic object which implements a set of interfaces, and you use the InvocationHandler to check each method call and decide what to do. This is a very powerful technique (and not limited to testing), as you can delegate method calls to other objects, etc.... It also insulates you from certain interface changes when you do this sort of delegation, as you don't declare each method. It adapts to the interface at runtine.
public static interface MyIntf {
String foo(String arg1);
}
InvocationHandler invocationHandler = new InvocationHandler() {
#Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (method.getName().equals("foo") &&
method.getParameterTypes().length == 1 &&
method.getParameterTypes()[0] == String.class) {
// do your mocking here. For now i'll just return the input
return args[0];
}
else {
return null;
}
}
};
MyIntf myintf = (MyIntf) Proxy.newProxyInstance(getClass().getClassLoader(),
new Class[] { MyIntf.class },
invocationHandler);
System.out.println(myintf.foo("abc"));
You cannot instantiate an interface, you need to work with one of its implementation. Since you have decided to forgo EasyMock (not sure why), then you need to either instantiate one of the existing interfaces implementations, or create a new one just for testing.
Hi I am facing a design problem which I think it should be quite common:
public abstract class Parent
{
...
public boolean itsOk()
{
return true;
}
public void execute()
{
if (itsOk()){
System.out.println("done");
}
}
}
I need to be able to override itsOK() function in any subclass inherited from 'Parent' even if arguments are different.
public class Example extends Parent
{
public boolean itsOK(int a)
{
if (a==1) return true;
else return false;
}
}
Then when I call execute, I want the subclass' itsOk() method to be invoked.
public static void main(String[] args) {
Example e=new Example();
e.execute();
}
This works ok if the subclass' itsOk() method has no arguments (like the 'Parent's method), so it's an overriding case, but how can I make it when arguments are different?
Call super.itsOk(); in your subclass' itsOk method.
That is, I'm assuming what you mean is you want to have an overload of itsOk defined in your subclass which does something new but also invokes the parent class' default implementation of itsOk.
As an aside, note the terminology: you're not overriding: to do that, the itsOk in your subclass must have the same method signature as in the parent class. Instead you're overloading creating a brand new method that just happens to have the same name.
You can use generics:
public abstract class Parent
{
...
public <T> boolean itsOk(T t)
{
return true;
}
public void execute()
{
if (itsOk()){
System.out.println("done");
}
}
}
public class Example extends Parent<Integer>
{
public boolean itsOK(Integer a)
{
if (a==1) return true;
else return false;
}
}
In such a case I would rather try to have the same method signature in the parent and the child class, ie. a real overwriting and not an overloading. Then, your parameter a could be a member of the class Example which would avoid the need for a parameter. Of course it strongly depends on the rest of the code.
The itsOk(int a) method in class Example is not overriding the itsOk() method in class Parent - it is an entirely separate method that doesn't have anything to do with the method in class Parent.
With what value of a do you want itsOk(int a) in Example to be called when you call itsOk() in Parent?
You could ofcourse add an itsOk(int a) method to class Parent; then the version in Example would be overriding that version, and in the execute() method you could call it:
public abstract class Parent {
public boolean itsOk() {
return true;
}
public abstract boolean itsOk(int a);
public void execute() {
if (itsOk(0)) {
System.out.println("done");
}
}
}
Without declaring an itsOk(int a) method in class Parent, you cannot call that method on a Parent object (or on an Example object, if the type of the variable referring to the object is Parent).
I don't think this is a common design problem.
When arguments are different it no longer is a case of Overriding. It is called Overloading which basically means that you have two distinct methods to call.