Invoke super class constructor of super class' parent class

I would like to invoke a constructor of a super class that is the parent of the direct super class. For instance:
class C extends class B, and class B extends class A.
From class C, is it possible to invoke class A's constructor without first invoking class B constructor?
Something like super.A() ??
Thanks.
Joe

try this,
abstract class GrandParent
      private Object pObj = null;
      protected Via via = new Via();
      protected class Via
         public Object doMethod1( Object obj )
            pObj = obj;
            return "GrandParent m1: " + pObj;
         public Object doMethod2( Object obj )
            pObj = obj;
            return "GrandParent m2: " + pObj;
         public Object get()
            return "gp get: " + pObj;
      public abstract Object doMethod1( Object obj );
      public abstract Object doMethod2( Object obj );
      public abstract Object get();
class Parent extends GrandParent
      private Object pObj = null;
      public Object doMethod1( Object obj )
      pObj = obj;
      return "Parent m1: " + pObj;
      public Object doMethod2( Object obj )
      pObj = obj;
      return "Parent m2: " + pObj;
      public Object get()
      return "p get: " + pObj;
public class GPMethod extends Parent
      public static void main( String[] args )
      GrandParent gp = new Parent();
      System.out.println( gp.doMethod1( "calling parent" ) );
      System.out.println( gp.doMethod2( "calling parent m2" ) );
      System.out.println( gp.get() );
      System.out.println( "" );
      System.out.println( gp.via.doMethod1( "calling via to GP" ) );
      System.out.println( gp.via.doMethod2( "calling via to GP m2" ) );
      System.out.println( gp.via.get() );
}

Similar Messages

How can a custom class call a function in "parent" class?

Say I have an application (ultrasimplified):
public class myApp {
myClass mc;
boolean foo=false;
public static void main(String[] args) {
mc = new myClass();
public static void myFunc(boolean blah) {
foo=blah;
in a separate .java file where my questions lie:
public class myClass {
boolean bar=true;
public void myClass() {
// this is wrong, but how would I do this:
foo = bar; // foo in myApp set to true
// or how would I call "myFunc()" in myApp from this class:
myFunc(bar);
my problem is that I've created a new class that I share between two applications so I could share the code. However, I want this class I created to call a function in the application class that instanciated it. Or alternatively, I would like to set a variable in the class that instanciated myClass.
How would go about this? I've used the "this" parameter in applets to pass the parent class to an inner class, but main() in applications doesn't allow the non-static "this":
myClass my = new myClass(this);
Is there something similar I can do?

You can let MyApp implement an interface and refer to that object in MyClass:
class MyApp implements Something {
main() {
MyApp app = new MyApp();
MyClass mc = new MyClass(app);
public void foo() { }
class MyClass {
Something app;
MyClass(Something app) {
this.app = app;
app.foo();
interface Something {
public void foo();
Better yet, you can let MyApp extend an abstract class that defines foo(). Then MyApp can override the foo() method. If later on, the abstract class needs to add a bar() method then default implementation can be done in the abstract class. If you make it an interface then all implementing classes will have to be updated to implement the new method.

Why does the child class need to implement the parent classes constructor?/

As I was playing around with some code I came across this point :
First Class
public class A {
     public int x;
     A(int i){
          x=i;
          System.out.println("A is initialised");
}Second Class extending it :
public class B extends A{
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// My guess is so that when i make an object of class B referring to class A it should make sense?
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public static void main(String args[]){
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      A b = new B(1); make an object of class B referring to class A it should work!!
      B c = new B(2);
      B d =(B) new A(2); --> gives class cast exception!
}I am little confused here, Can someone throw more light on it.
Thanks

You don't override constructors. However, every class, in it's constructor, must call some constructor from the class it's extending. In most cases this is simply super(). However, if your class does not have a default constructor (i.e. you've declared any other constructor, or the sub class does not have access to it, I.E. you've declared it private) then you must include a call to some other constructor in the super class. The constructor in the subclass does not have to be the same as the super class one, but you do have to invoke a constructor from the super class. I.E.
class A {
A(int i) {}
class B extends A {
B(String b) {
    super(0);
}

How to reference the class-instance, created in parent class.

Hi, I have following scenario. During compilation I am gettting error message -- "cannot resolve symbol - symbol : Variable myZ"
CODE :
under package A.1;
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under package A.2;
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How to reference the class-instance created in the parent class?

some corrections ...
under package A.1;
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under package A.2;
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How to listen to user actions in child class from parent class?

Hi,
I have a basic custom class ChildCustomForm that include a JTextField. In order to know what user types, I add a listener to
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its own userTyped flag.
My problem is: since I added listener in child class, I cannot get textfield and add listener again in parent class, so parent class will not be able to know as soon as user types (polling is not a good solution here).
I am wondering if there is a way to do this?
regards,

jack_wns wrote:
I have a basic custom class ChildCustomForm that include a JTextField. In order to know what user types, I add a listener to
this textbox:You want to listen for input into the textbox, correct? This may take the form of keyboard input, or could be a paste-text event in which case your keylistener will miss it. I recommend that you look into a DocumentListener here so you will catch any changes, be they keyboard or cut or paste.
My problem is: since I added listener in child class, I cannot get textfield and add listener again in parent class, so parent class will not be able to know as soon as user types (polling is not a good solution here).The observer pattern may work here.

Invoked super class constructor means create an object of it?

Hei,
i have create one class that extends another class. when i am creating an object of sub class it invoked the constructor of the super class. thats okay.
but my question is :
constructor is invoked when class is intitiated means when we create an
object of sub class it automatically create an object of super class. so means every time it create super class object.

Hi,
   An object has the fields of its own class plus all fields of its parent class, grandparent class, all the way up to the root class Object. It's necessary to initialize all fields, therefore all constructors must be called! The Java compiler automatically inserts the necessary constructor calls in the process of constructor chaining, or you can do it explicitly.
   The Java compiler inserts a call to the parent constructor (super) if you don't have a constructor call as the first statement of you constructor.
Normally, you won't need to call the constructor for your parent class because it's automatically generated, but there are two cases where this is necessary.
   1. You want to call a parent constructor which has parameters (the automatically generated super constructor call has no parameters).
   2. There is no parameterless parent constructor because only constructors with parameters are defined in the parent class.
   I hope your query is resolved. If not please let me know.
Thanks & Regards,
Charan.

Is it possible to override super class constructor?

Is it possible to override super class constructor form subclass?

However, you can achieve do something that looks similar to overriding.
class Parent {
Parent(int i, String s) {
    // do stuff
class Child extends Parent {
Child(int i, String s) {
    super(i, s);
    // do Child stuff here
new Parent(1, "abc");
new Child(2, "xyz");Although that's not overriding, it sort of looks similar. Is this what you were talking about?

Calling constructor of super class

Hello everyone! I'm a student. I hope I can find guidance. Here's the issue:
Super class: Property
Sub class: House
constructor of parent class:
protected Property(String id, char status, String address,
        String tenet, String landlord, long rent, char freq,
        long amtDue, String date, boolean repair, char tradesman)
        this.id = id;
        this.status = status;
        this.address = address;
        this.tenet = tenet;
        this.landlord = landlord;
        this.rent = rent;
        this.freq = freq;
        this.amtDue = amtDue;
        this.repair = repair;
        this.tradesman = tradesman;
        SimpleDateFormat formatter = new SimpleDateFormat("dd.MM.yy");
        this.dateDue = formatter.parse(date, new ParsePosition(0));
    }the constuctor of the sub class:
public House(String id, char status, String address,
        String tenet, String landlord, long rent, char freq,
        long amtDue, String dateDue, boolean repair, char tradesman,
        int broom, int proom, int throom, boolean garden,
        boolean garage, boolean heating)
    super(id, status, address, tenet, landlord, rent, freq,
        amtDue, dateDue, repair, tradesman);
    this.broom = broom;
    this.proom = proom;
    this.throom = throom;
    this.garden = garden;
    this.garage = garage;
    this.heating = heating;
    }I'm sure you notice I'm calling the constructor of the Property in House. That;s where the error is when i try to compile either class. This is the error it shows within the House class.
Object() in java.lang.Object cannot be applied to (java.lang.String,char,java.lang.String,java.lang.String,java.lang.String,long,char,long,java.lang.String,boolean,char)
Maybe its elementary? Thanks in advance..

You haven't pasted all the code so I can only guess that the class House does not extend Property class.
public class House extends Property
// put the constructor here
}If the House class does not extend Property (or any other class) it just extends (by default) the Object class, which does not have the constructor of Property class.
Hope it helps
Nick

Don't need call to super class constructor

Hi, I have
class A {
public A() { System.out.println("in A()");}
public class B extends A
{ public B() {
System.out.println("in B()");}
public static void main( String args[] ) {
B b = new B();}
I don't want the super class constructor to be called... What to do? Please tell me solution other than usage of parameterised constructor?

I don't want the super class constructor to be called... What to do? Can't be done. One of the constructors of the super class must be invoked. (Implicitly or explicitly)
Kaj

How to inherit super class constructor in the sub class

I have a class A and class B
Class B extends Class A {
// if i use super i can access the super classs variables and methods
// But how to inherit super class constructor
}

You cannot inherit constructors. You need to define all the ones you need in the subclass. You can then call the corresponding superclass constructor. e.g
public B() {
super();
public B(String name) {
super(name);
}

Constructor of derived-class has to call constructor of super-class?

In java, constructor of derived-class has to call constructor of super-class? there is no way to omit this step?

Correct. If you do not explicitly call the constructor, a call to the no-arg c'tor, super(), is automatically inserted.
It would be a mess to have it any other way. You'd be creating objects that are not completely initialized. They'd be in an invalid state.
Constructor rules:
1) Every class has at least one ctor.
1.1) If you do not define an explicit constructor for your class, the compiler provides a implicit constructor that takes no args and simply calls super().
1.2) If you do define one or more explicit constructors, regardless of whether they take args, then the compiler no longer provides the implicit no-arg ctor. In this case, you must explicitly define a public MyClass() {...} if you want one.
1.3) Constructors are not inherited.
2) The first statement in the body of any ctor is either a call to a superclass ctor super(...) or a call to another ctor of this class this(...) 2.1) If you do not explicitly put a call to super(...) or this(...) as the first statement in a ctor that you define, then the compiler implicitly inserts a call to super's no-arg ctor super() as the first call. The implicitly called ctor is always super's no-arg ctor, regardless of whether the currently running ctor takes args.
2.2) There is always exactly one call to either super(...) or this(...) in each constructor, and it is always the first call. You can't put in more than one, and if you put one in, the compiler's implicitly provided one is removed.

Can defualt inherited the Super Class constructor to sub class ?

Hi,
is it passible to inherit the super class constructor by defualt when extends the super class.
Thanks
MerlinRoshina

Constructor rules:
1) Every class has at least one ctor.
1.1) If you do not define an explicit constructor for your class, the compiler provides a implicit constructor that takes no args and simply calls super().
1.2) If you do define one or more explicit constructors, regardless of whether they take args, then the compiler no longer provides the implicit no-arg ctor. In this case, you must explicitly define a public MyClass() {...} if you want one.
1.3) Constructors are not inherited.
2) The first statement in the body of any ctor is either a call to a superclass ctor super(...) or a call to another ctor of this class this(...) 2.1) If you do not explicitly put a call to super(...) or this(...) as the first statement in a ctor that you define, then the compiler implicitly inserts a call to super's no-arg ctor super() as the first call. The implicitly called ctor is always super's no-arg ctor, regardless of whether the currently running ctor takes args.
2.2) There is always exactly one call to either super(...) or this(...) in each constructor, and it is always the first call. You can't put in more than one, and if you put one in, the compiler's implicitly provided one is removed.

Cannot use super(msg) in asbstract class constructor!!

Hi, I'm getting compiling errors (compiler says I must call super first thing I do from constructor, which is exactly what I'm doing!) when trying to call super(String msg) from my subclass constructor. Superclass is abstract and subclasses Exception, on which I also want to call super(msg), to initialize the Exception class with a String message.
What is wromg ? Please any help in resolving this issue will be highly appreciated...
/Alcoolio
abstract class SuperExceptionClass extends Exception{
void SuperClass(String msg){
super(msg);
void someCoolCommonMethod(){
//dostuff...
class SubExceptionClass1 extends SuperClass{
void SubClass(String msg){
super(msg);
}

Hi, I'm getting compiling errors (compiler says I must
call super first thing I do from constructor, which is
exactly what I'm doing!) when trying to call
super(String msg) from my subclass constructor.
Superclass is abstract and subclasses Exception, on
which I also want to call super(msg), to initialize
the Exception class with a String message.
What is wromg ? Please any help in resolving this
issue will be highly appreciated...
/Alcoolio
abstract class SuperExceptionClass extends Exception{
void SuperClass(String msg){
super(msg);
void someCoolCommonMethod(){
//dostuff...
class SubExceptionClass1 extends SuperClass{
void SubClass(String msg){
super(msg);
}First:
Constructor cannot have a return type. Not even void
Second:
Constructor should have same name as the class name. Otherwise it is a function. You can user "super()" only in constructor (although you could do super.xxx / super.xxx() in methods ).
abstract class SuperClass extends Exception{
SuperClass(String msg){ // change this
super(msg);
void someCoolCommonMethod(){
//dostuff...
class SubClass extends SuperClass{
SubClass(String msg){
super(msg);
}

How to override a method in an inner class of the super class

I have a rather horribly written class, which I need to adapt. I could simply do this if I could override a method in one of it's inner classes. My plan then was to extend the original class, and override the method in question. But here I am struggling.
The code below is representative of my situation.
public class ClassA
   ValueChecks vc = null;
   /** Creates a new instance of Main */
   public ClassA()
      System.out.println("ClassA Constructor");
      vc = new ValueChecks();
      vc.checkMaximum();
     // I want this to call the overridden method, but it does not, it seems to call
     // the method in this class. probably because vc belongs to this class
      this.vc.checkMinimum();
      this.myMethod();
   protected void myMethod()
      System.out.println("myMethod(SUPER)");
   protected class ValueChecks
      protected boolean checkMinimum()
         System.out.println("ValueChecks.checkMinimum (SUPER)");
         return true;
      protected boolean checkMaximum()
         return false;
}I have extended ClassA, call it ClassASub, and it is this Class which I instantiate. The constructor in ClassASub obviously calls the constructor in ClassA. I want to override the checkMinimum() method in ValueChecks, but the above code always calls the method in ClassA. The ClassASub code looks like this
public class ClassASub extends ClassA
   public ClassAInner cias;
   /** Creates a new instance of Main */
   public ClassASub()
      System.out.println("ClassASub Constructor");
   protected void myMethod()
      System.out.println("myMethod(SUB)");
   protected class ValueChecks extends ClassA.ValueChecks
      protected boolean checkMinimum()
         System.out.println("ValueChecks.checkMinimum (SUB)");
         return true;
}The method myMethod seems to be suitably overridden, but I cannot override the checkMinimum() method.
I think this is a stupid problem to do with how the ValueChecks class is instantiated. I think I need to create an instance of ValueChecks in ClassASub, and pass a reference to it into ClassA. But this will upset the way ClassA works. Could somebody enlighten me please.

vc = new ValueChecks();vc is a ValueChecks object. No matter whether you subclass ValueChecks or not, vc is always of this type, per this line of code.
// I want this to call the overridden method, but it does not, it seems to > call
// the method in this class. probably because vc belongs to this class
this.vc.checkMinimum();No, it's because again vc references a ValueChecks object, because it was created as such.
And when I say ValueChecks, I mean the original class, not the one you tried to create by the same name, attempting to override the original.

Inner classes can't access parent classes in constructor

I'm having a problem where I have class A, which has an Inner class B, which has it's own inner class C. In C's constructor (the inner most class), i'm trying to access a method of A (the top most class), and I get a NullPointerException with trace:
at mearns.finance.DefaultPortfolio.access$0(DefaultPortfolio.java:1)
at mearns.finance.DefaultPortfolio$AccountsEditor$AccountsTableModel.<init>(DefaultPortfolio.java:253)
In this case "DefaultPortfolio" is class A, AccountsEditor is class B, and AccountsTableModel is class C. The line given in the second stack trace element is the line in C's constructor which calls Class A's method.
Debugging, I stop inside C's constructor. Before anything happens, debugger says this$1 is null. Then I step, and it calls super(), and now this$1 is an instance of class B (AccountEditor), but it's own this$1 (which should be an instance of class A) is still null.
I'm calling C's constructor from within B's constructor (but not A's), not sure if that makes a difference.
Can anyone explain what's going on here, and (hopefully) how I can work around it?
Thanks for any help.
When i debug

hm, I really don't know what is happening but I want to tell you about something that is not nice in your code and possibly it could cause the error.
Code behaves somwhat strange when you pass this out of a constructor. You do this implicitly when you create an inner classe which implicitly gets a reference to the outer class. Also just simple method calls can cause such effects.
This is because the construction process it not finished but methods are already called.
Even worse: the sub classes constructor possibly did not even start. Special to java is the fact that a method call can lead to an overridden method of a sub class who's constructors has not even passed the super() command.
My guess now is that you have that some kind of this situation in your code. You create an inner class in a constructor. That inner class calls back a method on the outer class. Now say that the method you are calling is defined in a sub class who's constructor still stucks in super() call. There we are.
I found a thread in a news group that covers exactly this problem:
It is therefore a good idea only to call private methods from constructors (that should then also call only private methods). Also if inner classes are created in the constructor then they should not call any non trivial / non private methods of the outer class. Calling overridden methods out of constructors should be avoided strictly!
Perhaps this has nothing to do with your problem. I cannot tell for sure.
But this sounds quite interesting.
Please tell me if my guess was right and if not post simple code the illustrated your problem.
Here a simple example also throwing NullPointerException:
class Outer {
int i = 42;
abstract class InnerSuper {
    InnerSuper() {
      foo();
    abstract void foo();
class InnerSub extends InnerSuper {
    void foo() {
      System.out.println(i);
public void bar() {
    new InnerSub();
public static void main(String[] args) {
    Outer o = new Outer();
    o.bar();
} It causes a NullPointerException because the InnerSub constructor did not run. I copied the example from a news group thread i found.
http://groups.google.de/group/comp.lang.java.programmer/browse_thread/thread/897fba792d689b29/a1ba2ed708636a30?q=inner+class+outer+this+reference+NullPointerException&rnum=4&hl=de#a1ba2ed708636a30
Here is a even simpler example of strange behavior - even without NullPointerExceptions.
class A {
     A() {
          System.out.println(getName());
     String getName() {
          return "A";
class B extends A {
     String NAME = "B";
     String getName() {
          return NAME;
new B();It will output null instead of B.
regards
Sven

Invoke super class constructor of super class' parent class

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