Suppose I have two classes SuperClass
and SubClass
which extends SuperClass
, such as below:
public abstract class SuperClass {
private Object field1;
protected SuperClass(Object obj) {
setField1(obj);
}
public void setField1(Object obj) {
// perform some check on obj and
// then set field1 such that field1==obj
}
}
public class SubClass extends SuperClass {
public SubClass(Object obj) {
super(obj);
}
@Override
public void setField1(Object obj) {
super.setField1(obj);
// do some work that is necessary only when
// field1 is set through SubClass.setField1()
}
}
What I need is, when I create an object of SubClass
, I need method SuperClass.setField1()
to be called from inside SuperClass
constructor, not SubClass.setField1()
. But with the above code, method SubClass.setField1()
is called which causes a NullPointerException
to be thrown, since the work done in SubClass.setField1()
is performed on a field that's yet null.
Is there any way to explicitly call SuperClass.setField1()
from inside SuperClass
constructor?
You could move said method body to a private method and let the default method (the one which may be overridden by the subclass) delegate to the former. See this example
public abstract class SuperClass {
private Object field1;
protected SuperClass(Object obj){
// call the safe implementation
setField1Safe(obj);
}
public void setField1(Object obj){
// just delegates
setField1Safe(obj);
}
private void setField1Safe(Object obj){
// perform some check on obj and
// then set field1 such that field1==obj
}
}
public class SubClass extends SuperClass{
public SubClass(Object obj){
super(obj);
}
@Override
public void setField1(Object obj){
super.setField1(obj);
// do some work that is necessary only when
// field1 is set through SubClass.setField1()
}
}
That way the sub class can still override setField1
but if you really depend on the implementation then you can call the private setField1Safe
method.
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