Why does Java not support multiple inheritance of classes?

If a class could extend two classes with the same method, Java would not know which one to use. This is the diamond problem. So a class can extend only one class.

But a class can implement many interfaces. Since interfaces can have default methods now, a clash must be solved by the class:

interface A { default String hi() { return "A"; } }
interface B { default String hi() { return "B"; } }

class C implements A, B {
    public String hi() {
        return A.super.hi() + B.super.hi();      // you choose
    }
}

public class Main {
    public static void main(String[] args) {
        System.out.println(new C().hi());
    }
}

See Java Interfaces.

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