CODEWITHSUNDEEP
javainheritance
jonderry
jonderry

Reputation: 23633

Create a subclass from an instance to override a few methods?

For testing purposes, I want to replace the implementation of a few methods of an object that implements some interface. One way of doing this would be to create a new object, passing the instance as a parameter to the constructor, and manually recreating all of the methods to use the instance's methods for all but a couple of methods, which would be overridden for testing purposes. Unfortunately, the interface has a large number of methods, which makes this option tedious.

Is there some way to create an object that is a "subclass of an instance of an object" in the sense that it simply calls the instance's method's for all calls except when overridden?

Upvotes: 0

Views: 261

Answers (3)

pajton
pajton

Reputation: 16226

Dynamic Proxy Classes may be a way to go. I have never used it before, however it is a viable mechanism to catch every method invocation and decide whether to invoke old method or do something else and/or extra.

The link I provided has even an example of DebugProxy which may be helpful for you.

Upvotes: 3

Uhlen
Uhlen

Reputation: 1778

Create a mock using some mocking framework like Mockito:

MyComplexInterface mock = Mockito.mock(MyComplexInterface.class);
Mockito.when(mock.someMethod()).thenReturn("some value");

Mockito are able to mock both interfaces and concrete classes.

Upvotes: 4

Amir Afghani
Amir Afghani

Reputation: 38521

For testing purposes, I want to replace the implementation of a few methods of an object that implements some interface.

Simply create a class that extends the current concrete class, and override only those methods from the interface you want to test.

public class ForTest extends X {

    @Override
    public void m1() { 
        .
        .
        .
    }

}

public class X implements Z{ 

//all the overrides

}

interface Z { 

//lots of methods

}

Upvotes: 1

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