[ACCEPTED]-Java: how to initialize child when super constructor requires parameter-inheritance
Assuming var is private and you need to set the 7 value with the constructor (which seems 6 to be the point of the question, otherwise 5 there are many easy solutions), I would 4 just do it with a static factory-like method.
class B extends A {
int var2;
public static B createB(int x, int y) {
x = f(y);
return new B(x, y);
}
public B(x, y) {
super(x);
this.var2 = y;
}
}
something 3 like that. You have no choice, as explicit 2 constructor invocation must happen on the 1 first line of the wrapping constructor.
You can do it like this :
class B extends A {
int var2;
public B(int x, int y) {
super(calculateX(y));
var2 = y;
}
private static int calculateX(int y) {
return y;
}
}
Calling a static 2 method is the only thing you can do before 1 calling the superclass constructor.
Alternative to hvgotcodes, since it looks 1 like you also want to set A's variable...
class B extends A {
int var2;
public B(int x, int y) {
super(x);
var2 = y;
x = f(y);
super.var = ...;
}
}
Another approach could be to add a protected 4 constructor without parameters to A that 3 relies on lazy initialization:
class A {
int var;
public A(int x) {
var = x;
}
/**
* Just use this constructor if you initialize var
*/
protected A(int x) {
}
}
class B extends A {
int var2;
public B(int x, int y) {
super();
var2 = y;
var = f(y);
}
}
But that's 2 hard to document, not very obvious to team 1 members and shouldn't be used for an api.
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