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class A {
 
public void ml(){
    mx();
}
 
public static void main(String[] args){
 
    A a = ( B) new C(); 
    a.m1();
    B b = (B) new A(); 
    b.m1();
}
 
public void mdx(){ 
     System.out.print(10);
}
}
 
 
class B extends A{
public void mx(){
    System.out.print(30);
}
}
 
class C extends B {
public void mx(){
    System.out.print(40);
}
}

Main.java:4: error: cannot find symbol
    mx();
    ^
  symbol:   method mx()
  location: class A
Main.java:10: error: cannot find symbol
    a.m1();
     ^
  symbol:   method m1()
  location: variable a of type A
Main.java:12: error: cannot find symbol
    b.m1();
     ^
  symbol:   method m1()
  location: variable b of type B
3 errors

Standard output is empty