Multiple Inheritance is not supported by java in order to
avoid ambiguity between variables of different classes and
to rudece memory overloading.

There is a big reason behind that(java does not support 
multiple inheritance). Please go through the following 
example.

1. Assume that java is supporting multiple inheritance 

class A {

  void m1() {
        // implement method 
  }
}

class B {
  void m1() {
        // implement method
  }
}
//As for the assumption (1) the following code will compile

class C extends A,B {

   public static void main( String s[]) {
   
     C c = new C();
     c.m1();
   }
}

Note : In main method i am calling c.m1() method In this 
situation which super class m1 method has to call (from A 
or B) JVM will confuse.

So our assumtion(1) is wrong .

This is the  reason why java does not support multple 
inheritance through classes.

Note : This same cocept is applicable for classes.

ya java don't support multiple interitence but by achieving
it the interface are came

The famous "diamond shaped problem " is the reason behind NOT using multiple inheritance in java.
   check out this link for full details
       http://en.wikipedia.org/wiki/Diamond_problem

java support multiple inheritance not through the use of
class, but through the implementation of interface we can
achieve multiple inheritance.

By using interface we can implement multiple interfaces for
a class which can solve the problem of our multiple inheritance.

Java Does not support Multiple inhertiance through class
because ambiguity between variables  of different classes
and to rudece memory overloading.and another reason java 
extended only one class at time

java support Multiple inhertiance through interfaces.because
java class implements any number of interface at  time

Why cant we face same ambiguity when we declare variables?  
interface A{
int i = 10;
}
interface B{
int i = 20;
}
Class C implement A, B{
what is the value of C.i?
}