Question

I have a base class and a derived class and another external class.
I try to update a value in the base class from the external class and
access it from the derived class.

My class structure is like below:

class B:{

bool flag;

setFlag(bool value){
flag = value;
}
printFlag(){
print flag;
}

ExternalClass e = new ExternalClass(this);
}

class External {
B b = null;
External( B b){
this.b = b;
}
b.setFlag(true);

}

Class Derived : extends B{

printFlag();
}

Here though i have set the flag to true, the print method prints false.
I dont have a clue as to what is happening . Kindly help me out.

Answer 1

Here is some code that does what you wish:

class Derived extends B{
    public Derived(){
        super(); 
        // this is the important bit, by calling super() you call the parent classes
        // constructor, which in this case changes the attribute "flag"
        // by using the constructor of the external class on the class
    }
}

class B {
    boolean flag;
    ExternalClass e;

    public B(){
        e = new ExternalClass(this);
    }

    public void setFlag(boolean value) {
        flag = value;
    }

    public void printFlag() {
        System.out.println(flag);
    }

}

class ExternalClass {

    B b = null;

    public ExternalClass(B b) {
        this.b = b;
        b.setFlag (true);
    }
}