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.