Why there is no multiple inheitance in java?

[Neha Deshmukh]

I am fresher. I want to improve java skills. So help me.

[dswastik]

Why not multiple inheritance? - JavaWorld

[Neha Deshmukh]

sir i want only explanation not a link

[subith86]

the reason is very well described in that link.

[JosAH]

I am fresher. I want to improve java skills. So help me.

Java doesn't have multiple inheritance (MI) of implementation; it does have MI of type (interface). MI of implementation is a burden because it needs carefull fiddling with the 'this' pointer and Java tries to keep things simple so it doesn't implement it. If a class D already extends a class B and you also want to 'extend' it a class C, class C needs to implement an interface CI, so you have:

interface CI { void aMethod(); }
class C implements CI { ... }
class D extends B { ... }

Now create an instance of C and pass it to D as follows:

class D extends B implements CI {
   private C c;
   public D(C c) { this.c= c; }
   public void aMethod() { c.aMethod(); }
}

As you can see a B passed the call to aMethod() to its member c and it implements CI, just as a C does. Through composition you have the same effect as if MI of implementation were allowed.

kind regards,

Jos

[sanjeevtarar]

There is a way of Multiple inheritances in Java using Interfaces

One reason why multiple class inheritance in not allowed because class describe HOW to do a thing and in interface describes only WHAT to do that's why it is allowed at interface level only

because in case of class, a subclass can not decide which implementation to pick

[sunde887]

Say you subclassed two different classes, and both classes have a method of the same name, how would the compiler be able to tell the difference?

This is one of the things that makes multiple inheritance more difficult. In the end it comes down to the fact that using single inheritance is easier.

[JosAH]

Say you subclassed two different classes, and both classes have a method of the same name, how would the compiler be able to tell the difference?

C++ can't tell the difference either, it picks the implementation that is first in the list of extended classes, i.e.

class C : B1, B2 { ... }

if a method M would've been present in both B1 and B2, the implementation of M in B1 is chosen because B1 comes first in the list.

kind regards,

Jos

[sunde887]

Ah, thanks for the information, one of the books I had read said that was one fault of multiple inheritance.