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Call the test method differently
However, the call of the method named test in the object instantiated from the class named B is somewhat different. The difference is identified by the code in the followingfragment.
void doIt(){
Base myVar1 = new Base();myVar1.test();
myVar1 = new A();myVar1.test();
myVar1 = new B();myVar1.test();
X myVar2 = (X)myVar1;myVar2.test();
System.out.println("");}//end doIt() Calling test method on Base-type reference
In Question 9 , and in the above code fragment as well, the method named test was called on each of the objects using a reference stored in a reference variable of type Base .
Calling the overridden version of test method
This might be thought of as calling the overridden version of the method, through polymorphism, without regard for anything having to do with theinterfaces.
Calling test method on interface-type reference
Then the code shown above calls the same method named test on one of the same objects using a reference variable of the interface type X .
Only one test method in each object
Keep in mind that each object defines only one method named test . This single method serves the dual purpose of overriding the method having thesame signature from the superclass, and implementing a method with the same signature declared in each of the interfaces.
Implementing the interface method
Perhaps when the same method is called using a reference variable of the interface type, it might be thought of as implementing the interface methodrather than overriding the method defined in the superclass. You can be the judge of that.
The same method is called regardless of reference type
In any event, in this program, the same method is called whether it is called using a reference variable of the superclass type, or using a reference variable of the interface type.
Illustrates the behavior of signature collisions
The purpose of this and Question 9 is not necessarily to illustrate a useful inheritance and implementation construct. Rather, these twoquestions are intended to illustrate the behavior of Java for the case of duplicated superclass and interface method signatures.
C. Base A B
A question regarding signature collisions
The question often arises in my classroom as to what will happen if a class inherits a method with a given signature and also implements one or moreinterfaces that declare a method with an identical signature.
The answer
The answer is that nothing bad happens, as long as the class provides a concrete definition for a method having that signature.
Only one method definition is allowed
Of course, only one definition can be provided for any given method signature, so that definition must satisfy the needs of overriding the inheritedmethod as well as the needs of implementing the interfaces.
An example of signature collisions
The following fragment defines a class named Base that defines a method named test . The code also defines two interfaces named X and Y , each of which declares a method named test with an identical signature.
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