Why java does not support multiple inheritance or diamond problem in multiple inheritance

package com.javaeasy;

class A {

public void add() {

System.out.println("I am in class A");

}

}

class B extends A {

public void add() {

System.out.println("I am in class B");

}

}

public class NotSupportingMultipleInheritance extends A,B {

//Confusion seen here and cant decide to call class A or B method

//Diamond Problem

public static void main(String[] args) {

// TODO Auto-generated method stub

NotSupportingMultipleInheritance obj=new NotSupportingMultipleInheritance();

obj.add();

}

}