why Java class can extends only one class but implements many interfaces? [duplicate]

Question

In C++, you can extends many classes, so what's the advantages of this design in Java that a class can only extends one class ? Since interface is a pure kind of class(abstract class actually), why not limit the number of interfaces implementation just like class extension ?

Answer 1

Being able to extend only one base class is one way of solving the diamond problem. This is a problem which occurs when a class extends two base classes which both implement the same method - how do you know which one to call?

A.java:

public class A {
    public int getValue() { return 0; }
}

B.java:

public class B {
    public int getValue() { return 1; }
}

C.java:

public class C extends A, B {
    public int doStuff() { 
        return super.getValue(); // Which superclass method is called?
    }
}

Since interfaces cannot have implementations, this same problem does not arise. If two interfaces contain methods that have identical signatures, then there is effectively only one method and there still is no conflict.