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Java - Implement two interfaces with different methods

Say there are two interfaces, which have different methods. I am implementing both interfaces in a class and using methods of both the interfaces.
interface A { void show1(); }
interface B { void show(); }
public class test implements A, B{
#Override
void show1(){
System.out.println("show1");
}
#Override
void show(){
System.out.println("show");
}
}
Definition of Multiple Inhertiance:
Multiple inheritance is a feature of some object-oriented computer programming languages in which an object or class can inherit characteristics and features from more than one parent object or parent class.
Question
Can I say what I did in my program is Multiple Inheritance ? If No, Why ?
Note
I am using Java 7.

No. Because main purpose of interface is abstraction, which means hide implementation details from outside. So if you implement one or more interfaces, that relationship is a like a relationship and not is a relationship.
Another purpose of using interfaces is loose coupling between classes. (side outcome of abstraction).
See this is a nice example

I think implementation of multiple interfaces is not multiple inheritance.
Your object may have implementation of multiple interfaces. For example your Car object may have interface like BreakStatus, FuelTank interfaces but it's not defined Car as a sub-type/derived-type of BreakStatus, FuelTank.
Inheritance is: One object extends other object(parent) properties and/or behaviors.
Java object does not support multiple inheritance(extending multiple object) something like class Child extends Parent1, Parent2 {}
N.B. Java interfaces support extending multiple interfaces, e.g. interface I3 extends I1, I2 {}

Yes what you did in your program is multiple inheritance.
The Java programming language supports multiple inheritance of type, which is the ability of a class to implement more than one interface. An object can have multiple types: the type of its own class and the types of all the interfaces that the class implements.
https://docs.oracle.com/javase/tutorial/java/IandI/multipleinheritance.html

Yes you are achieving multiple inheritance using multiple interface, where you can inheriting the definition of two different interfaces.
In java, multiple Inheritance is achieved using Multiple interfaces. Methods in an interface are always abstract by default, which doesn’t let them to give their implementation (or method definition ) in interface itself.

Java allowing multiple inheritance

I am confused regarding a concept in multiple inheritance.
I have three classes A, B and C.
Class A {
// ...
}
Class B extends A {
// ...
}
Class C extends B {
// ...
}
I know this is a bad practice of multiple inheritance and I also read java allows multiple inheritance through interfaces. But I am not getting any error in the above code. Please can anyone explain me with a clear example without using interface.
Thanks!!

This is not multi-inheritance. Each class has exactly one direct super class. If your example was considered multi-inheritance, you wouldn't be able to use the extends keyword at all, since each class already extends by default the Object class.
Multi-inheritence would be
class C extends A,B {}
And that's illegal in Java.

Your code does not contain multiple inheritance, and is, indeed, legal Java syntax. Multiple inheritance refers to a case where a class directly extends two superclasses. For example:
public class MyClass extends MyFather, MyMother {
}
Note that this is, of course, illegal Java syntax.

"Multiple inheritance" in Java basically means inheriting multiple interfaces, not inheriting multiple implementations.
Now, there is a new feature of Java 8 that allows you to do something like multiple inheritance of actual implementations, via interfaces and something called default methods. I would strongly encourage you to really master the basics of Java first before trying them. Once you are ready, here is a good tutorial on default methods.

The code you have written above is an example of Multilevel inheritance not Multiple Inheritance.
Multiple Inheritance is like :
class A extends B,C {
//this code is not valid in JAVA
}
And, if you want to use interfaces for implementing a structure like multiple inheritance, then you could use:
interface test_interface1{
/*all the methods declared here in this interface should be the part
** of the class which is implementing this current interface
*/
}
Similarly :
interface test_interface2{
}
So, create a class TestClass like :
class TestClass implements test_interface1,test_interface2 {
//now you have to use each and every method(s) declared in both the interfaces
// i.e. test_interface1 & test_interface2
}
You could also use a syntax like:
class TestClass extends AnyClass implements test_interface1,test_interface2 {
/* but do keep in mind - use extends keyword before implements
** and now you know you cannot use more than 1 class names with extends keyword
** in java.
*/

java generics, how to extend from two classes?

I want to have a Class object, but I want to force whatever class it represents to extend class A and also class B.
I can do
<T extends ClassA & ClassB>
but it is not possible to extend from both classes, Is there a way to do this?

In java you cannot have a class which extends from two classes, since it doesn't support multiple inheritance. What you can have, is something like so:
public class A
...
public class B extends A
...
public class C extends B
...
In your generic signature, you can then specify that T must extend C: <T extends C>.
You could give a look at Default Methods (if you are working with Java 8), which essentially are methods declared within interfaces, and in Java, a class can implement multiple interfaces.

A simple way for this problem is inheritance.
public class A { // some codes }
public class B extends A { }
<T extends A>

Java does not have multiple inheritance as a design decision, but you may implement multiple interfaces.
As of Java 8 these interfaces may have implementations.
To use multiple classes there are other patterns:
If the parent classes are purely intended for that child class, but handle entirely different aspects, and were therefore separated, place them in a single artificial hierarchy. I admit to doing this once.
Use delegation; duplicate the API and delegate.
Use a lookup/discovery mechanism for very dynamic behaviour.
public T lookup(Class klazz);
This would need an API change, but uncouples classes, and is dynamic.

Java instance vs Abstract Classes and methods

I am new to Java and have been reading up on its main topics. I recently covered abstract classes and instances. I have read their definitions so its not a definition i am looking for.
I need help understanding why I would need to use an interface. All the examples I have seen of interfaces on java tutorials online to me seem like they can be implemented using an abstract class/method combination instead.
Is there a common scenario where only an interface can be used to solve the issue and a combination of abstract class/method would not?

A good example from the Java APIs is the LinkedList class.
As you can see from the link, it implements both the List and the Deque interfaces (as well as a few others), allowing it to be used whenever one or the other is needed. This would not have been possible using only abstract classes.

An interface defines a new secondary
datatype in Java.
It (interface) is a group of final variables
and abstract methods only.
The members of an interface are "public"
by default. Infact private and protected
modifiers are not allowed in an interface.
An interface is a reference type only
its objects cannot be created.
An interface can inherit another interface
but cannot inherit any class.
A class cannot inherit any interface but
it (a class) can implement zero to many
interfaces.
If a class implements interfaces then
1) It has to override all the abstract
methods of all the implemented interfaces.
2) Type compatibilty gets created between
the interface and the class. It allows an
interface reference can refer to object
of implementing class.
interface Iface
{
int x = 3;//final and public by default
void f();//abstract and public by default
}
interface AnotherI extends Iface
{
//more declarations possible here
}
class InterfaceDemo implements Iface
{
public void f()
{
int i;
for(i =0 ; i< x; i++)
System.out.println("Interfaces are widely used");
}
public static void main(String args[])
{
Iface ref = new InterfaceDemo();
ref.f();//allowed
//ref.newMethodsOfClass();//not allowed
}
}

The main difference is that you can only extend one class but you can implement multiple interfaces.
This can be important if you want to (for example) implement a listener while also extending another class. Note though that in many cases you are better off using an anonymous inner class to do the listening.

Java does not support polymorphic inheritance - where a class can extend multiple classes. This choice was made to avoid the problems associated with hierarchical conflict resolution (where a method exists in both parent classes - which one do you use?). In simple parlance, in java there can only be one "is a" relationship.
However, to allow a form of polymorphism, interfaces were introduced. These are hollow templates for which the class must provide implementations, and offer a way of creating a "look like a" relationship. While only allowing an object to "be" a instance of one (parent) class, it may "look like" any number of interfaces.
By taking inheritance out of interfaces, it allows cross-cutting concepts to be handled - ie where classes of completely different inheritance structures may nevertheless share some abstract similarity. A good example from the JDK is Serializable, which is a marker interface (one without methods). Virtually any class has the possibility to be serializable, but virtually all serializable classes don't share any of their inheritance hierarchy. This concept couldn't be handled with abstract classes - you have to step out of the class hierarchy to achieve it - ie interfaces is the only way to do it.

Can an interface extend multiple interfaces in Java?

Can an interface extend multiple interfaces in Java? This code appears valid in my IDE and it does compile:
interface Foo extends Runnable, Set, Comparator<String> { }
but I had heard that multiple inheritance was not allowed in Java. Why does there appear to be an exception for interfaces?

Yes, you can do it. An interface can extend multiple interfaces, as shown here:
interface Maininterface extends inter1, inter2, inter3 {
// methods
}
A single class can also implement multiple interfaces. What if two interfaces have a method defining the same name and signature?
There is a tricky point:
interface A {
void test();
}
interface B {
void test();
}
class C implements A, B {
#Override
public void test() {
}
}
Then single implementation works for both :).
Read my complete post here:
http://codeinventions.blogspot.com/2014/07/can-interface-extend-multiple.html

An interface can extend multiple interfaces.
A class can implement multiple interfaces.
However, a class can only extend a single class.
Careful how you use the words extends and implements when talking about interface and class.

From the Oracle documentation page about multiple inheritance type,we can find the accurate answer here.
Here we should first know the type of multiple inheritance in java:-
Multiple inheritance of state.
Multiple inheritance of implementation.
Multiple inheritance of type.
Java "doesn't support the multiple inheritance of state, but it support multiple inheritance of implementation with default methods since java 8 release and multiple inheritance of type with interfaces.
Then here the question arises for "diamond problem" and how Java deal with that:-
In case of multiple inheritance of implementation java compiler gives compilation error and asks the user to fix it by specifying the interface name.
Example here:-
interface A {
void method();
}
interface B extends A {
#Override
default void method() {
System.out.println("B");
}
}
interface C extends A {
#Override
default void method() {
System.out.println("C");
}
}
interface D extends B, C {
}
So here we will get error as:-
interface D inherits unrelated defaults for method() from types B and C interface D extends B, C
You can fix it like:-
interface D extends B, C {
#Override
default void method() {
B.super.method();
}
}
In multiple inheritance of type java allows it because interface doesn't contain mutable fields and only one implementation will belong to the class so java doesn't give any issue and it allows you to do so.
In Conclusion we can say that java doesn't support multiple inheritance of state but it does support multiple inheritance of implementation and multiple inheritance of type.

Can an interface extend multiple interfaces in java?
Answer is: Yes.
According to JLS
An interface may be declared to be a direct extension of one or more
other interfaces, meaning that it implicitly specifies all the member
types, abstract methods, and constants of the interfaces it extends,
except for any member types and constants that it may hide.

You can extend multiple Interfaces but you cannot extend multiple classes.
The reason that it is not possible in Java to extending multiple classes, is the bad experience from C++ where this is possible.
The alternative for multipe inheritance is that a class can implement multiple interfaces (or an Interface can extend multiple Interfaces)

I think your confusion lies with multiple inheritance, in which it is bad practise to do so and in Java this is also not possible. However, implementing multiple interfaces is allowed in Java and it is also safe.

A Java class can only extend one parent class. Multiple inheritance is not allowed. Interfaces are not classes, however, and an interface can extend more than one parent interface.
for example, take a look here: http://www.tutorialspoint.com/java/java_interfaces.htm