Java编译器如何生成重载和覆盖方法代码

package simplejava;

class A {
    public void M(int i) {
        System.out.println("int");
    }

    public void M(String s) {
        // this is an overloading method
        System.out.println("string");
    }
}

class B extends A {
    public void M(int i) {
        // this is overriding method
        System.out.println("overriden int");
    }
}

public class Q13 {

    public static void main(String[] args) {
        A a = new A();
        a.M(1);
        a.M("abc");
        A b = new B();
        b.M(1234);
    }

}