Sub class calls super in constructor

when a sub calss calls super() in its constructor is it overriding the constructor of base class ?
Class A {
A(Strin neme){
class B extend A{
B(){
super("test")
Systemout......
I donot know the term explaning this feature is it called overriding constructor?

miro_connect wrote:
so how to describe this code, are there any terms to explain this methodology to not technical guys ?Yeh. "Magic". Seriously. There's little point explaining such things to non-technical people. Ever tried to teach your mum how to program a VCR?
By definition, non-tech people will simply not understand what you're on about, and won't need to.

Similar Messages

Trouble assigning sub class to super class array

Hi,
I would greatly appreciate some help with the following:
I want to assign a sub class to a super class array but the following code does not work
where the board is comprised of the super class
     private static void makeMove( int X, int Y, int moveX, int moveY )
          ChessPiece tempChessPiece = ( ChessPiece ) board[ X ] [ Y ];
          board[ X ] [ Y ].setType( UNDEFINED );
          board[ moveX ] [ moveY ] = tempChessPiece;
     }

I have got this code to work but it does not appear
to be very efficient to me as i dont recycle the
objects.
Any thoughts?The objects will be recycled by the garbage collector. It's very efficient so there's very little performance penalty in creating objects and releasing objects.
Still, another alternative is to represent an empty square with null. In that case the code becomes,
private static void makeMove( int selectedX, int selectedY, int moveToX, int moveToY ) {
   board[moveToY][moveToX] = board[selectedX][selectedY]; // piece to new position
   board[selectedX][selectedY] = null; // remove from old
}I don't know your exact design but that should work. It's kind of natural too. If a square is empty there's no piece object there at all. No new object has to be created and that explicit cast is gone.

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.

Even i call this() paramerterised constuctor in my class, Is super class su

Even i call this() paramerterised constuctor in my class, Is super class super() parameter less constuctor invokes?
I have excuted the following program. And result will be as follows:
Grandparent() constructor
Parent 25 constructor
Parent() constructor
Child() constructor
The program is below:
class ConstructorChain {
public static void main(String[] args) {
Child c = new Child();
class Child extends Parent {
Child() {
System.out.println("Child() constructor");
class Parent extends Grandparent {
Parent() {
this(25);
System.out.println("Parent() constructor");
Parent(int x) {
System.out.println("Parent(" + x + ") constructor");
class Grandparent {
Grandparent() {
System.out.println("Grandparent() constructor");
for this my excepected answer is
Parent 25 constructor
Parent() constructor
Child() constructor
because in parent class i defined this() constructor so, as my undersatnd is it never call Grand Parent Constructor as it is default parameterless constructor.
please Advise me
Aruna

You can't initialize a class without it's super classes constructor being run. So even if you call another constructor (of the same class), the parent classes constructor will still be called.

[OO Concept] Make a parent class perform code after constructor calls?

Hello,
I want to do something like this:
class Parent {
   Parent(){
      // do some parent stuff
   private void postConstruction(){
      // parent and all subclasses have completed construction, now do some post-construction code
      // analyze some of the child construction stuff
class Child extends Parent{
     Child(){
       // do some child stuff
     public static void main(String[] args){
          Child child = new Child();
}I assume I am having this problem because of bad OO design. What would be the problem way to design this so that the parent can check the values of its members after all of its subclasses have been constructed?
Thanks..

You can certainly call the postConstruction() method from your Parent constructor. But then (as you can see) it will be called before anything in your Child constructor. Bad design? Yes, bad design of the Java language in my opinion. It should have allowed the user to control the order of initialization more. But it doesn't. So you can't do that. Which basically means you can't use the constructor to construct your objects. You'll have to call some other method where you aren't required to call super.postConstruction() at the beginning.

Exception in super and sub class

when super class method throws an exception then sub class overridden method can throws child exception but when we talk about constructor why we throws parent class exception in derived class constructor????

tcbhardwaj wrote:
C() throws Throwable // why here parent of Exception class
void ok() throws ArithmeticException // why here child of RunTimeException classFirst, you never need to declare a throws clause for unchecked exceptions--RuntimeException, Error, and their descendants.
However, there are a couple of general rules for checked exceptions (such as IOException, SQLException, etc.). As you're studying these, keep in mind that a throws clause is a contract that promises what the method will not do. In particular, it doesn't promise that the method will throw those exceptions. It promises that it will not throw any other checked exceptions not covered by that throws clause.
1. A child method that overrides a parent method cannot throw any checked exception outside what's covered by the parent's throws clause. So if the parent method declared throws IOException, the child cannot declare throws Exception, or throws SQLException, because both of those are outside the IOException "sub-hierarchy."
2. A child method that overrides a parent method can declare to throw less than the parent throws. This is because, if the parent promises not to throw outside of some set, and the child promises not throw outside of a subset of that set, then clearly he's also not throwing outside of the parent's set. If the parent method declares throws SQLException, IOException, then the child can declare no exceptions at all, or just SQLException, or just IOException, or any combination of any of the subclasses of SQLE and IOE.
Rules 1 and 2 do not apply in the case of constructors, because no constructor can ever override another constructor.
3. When any method or constructor, A, invokes any other method or constructor, B, then any checked exception declared to be thrown by B must be either caught or declared to be thrown by A. If A catches or throws a parent of an exception thrown by B, then he's also implicitly catching or throwing the one that B mentions.

Instantiation of similar object over a super class deciding the sub class

Hello all
First, sorry if I'm duplicating an already answered question. I didn't searched very deep.
Initial position:
I have 2 Object (A1 and A2) which share the most (about 90%) of their instance variables an the associated methods. The values of the instance variables are retrieved in the real implementation from a stream. Depending of the data of the stream, I have to instantiate either a A1 or A2 object.
A test implementation (using an int in case of the stream):
The super class A:
package aaa;
public class A
protected int version = -1;
protected String name = null;
protected AE ae = null;
protected A()
protected A(int v)
    // Pseudo code
    if (v > 7)
      return;
    if (v % 2 == 1)
      this.version = 1;
    else
      this.version = 2;
public final int getVersion()
    return this.version;
public final String getName()
    return this.name;
public final AE getAE()
    return this.ae;
}The first sub class A1:
package aaa;
public final class A1 extends A
protected A1(int v)
    this.version = v;
    this.name = "A" + v;
    this.ae = new AE(v);
}The second subclass A2:
package aaa;
import java.util.Date;
public final class A2 extends A
private long time = -1;
protected A2(int v)
    this.version = v;
    this.name = "A" + v;
    this.time = new Date().getTime();
    this.ae = new AE(v);
public final long getTime()
    return this.time;
}Another class AE:
package aaa;
public class AE
protected int type = -1;
protected AE(int v)
    // Pseudo code
    if (v % 2 == 1)
      this.type = 0;
    else
      this.type = 3;
public final int getType()
    return this.type;
}To get a specific object, I use this class:
package aaa;
public final class AFactory
public AFactory()
public final Object createA(int p)
    A a = new A(p);
    int v = a.getVersion();
    switch (v)
    case 1:
      return new A1(v);
    case 2:
      return new A2(v);
    default:
      return null;
}And at least, a class using this objects:
import aaa.*;
public final class R
public static void main(String[] args)
    AFactory f = new AFactory();
    Object o = null;
    for (int i = 0; i < 10; i++)
      System.out.println("===== Current Number is " + i + " =====");
      o = f.createA(i);
      if (o instanceof aaa.A)
        A a = (A) o;
        System.out.println("Class   : " + a.getClass().getName());
        System.out.println("Version : " + a.getVersion());
        System.out.println("Name    : " + a.getName());
        System.out.println("AE-Type : " + a.getAE().getType());
      if (o instanceof aaa.A2)
        A2 a = (A2) o;
        System.out.println("Time    : " + a.getTime());
      System.out.println();
Questions:
What would be a better way to encapsulate the logic into their respective objects ? Is there a way to let the super class A itself identify the type of the object and then extend from A to either A1 or A2 ?
Thanks in advance
Andreas

Hello jduprez
First, I would thank you very much for taking the time reviewing my problem.
Just for the record: have you considered regular serialization? If you control the software at both ends of the stream, you could rely on standard serialization mechanism to marshall the objects and unmarshall them automatically.In my case, I can't control the other site of the stream. At the end, the data comes from a FileInputStream and there aren't objects on the other site, only pur binary data.
- It seems you have one such factory class. Then you already have encapsulated the "determine class" logic, you don't need to add such logic in superclass A.I thought from an OO view, that the super class A is responsible of doing that, but that's where the problem starts. So at the end, it's better doing it in the factory class.
- A itself encapsulates the logic to load its own values from the stream.
- A1 and A2 can encapsulate the logic to load their own specific value from a stream (after the superclass' code has loaded the superclass' attributes values).
My advise would be along the lines of:
public class A {
.... // member variables
public void load(InputStream is) {
... // assign values to A's member variables
// from what is read from the stream.
public class A1 extends A {
... // A1-specific member variables
public void load(InputStream is) {
super.load(is);
// now read A1-specific values
public class AFactory {
public A createA(InputStream is) {
A instance;
switch (is.readFirstByte()) {
case A1_ID:
a = new A1();
break;
case A2_ID:
a = new A2();
break;
a.load(is);
}The example above assumes you have control over the layout of the data in the stream (here for a given A instance, the attributes defined in A are read first, then come the subclass-specific attributes.
The outcome is: you don't have to create a new A( ) to later create another instance, of a subclass.I like the idea. In the AFactory, is the "A instance;" read as "A a;" ?
Is there a way to let the super class A itself identify the type of the object and then extend from A to either A1 or A2 ?Note I initially read this question as "can an instance of a class mutate into another class", to which the answer is no (an object has one single, immutable class; it is an instance of this class, and of any superclass and superinterface, but won't change its class at runtime).Yes, I have been thinking about a way for mutating into a subclass to keep the already initialized values from the A class without copying or parsing again. But preventing an instance of an A class will be my way. So, in this aspect, Java didn't changed in the last 10 years... It's a long time ago I've used Java for some real projects.
You can, however, create an instance of another class, that copies the values off a priori A instance. Your example code was one way, another way could be to have a "copy constructor":
public class A {
public A(A model) {
this.att1 = model.att1;
this.att2 = model.att2;
public class A1 {
public A1(A model) {
super(model);
... // do whatever A1-specific business
)Still, I prefer my former solution less disturbing: I find the temporary A instance redundant and awkward.Nice to know. I prefer the first solution too.
Thank you again for the help and advices. My mind is searching sometimes for strange solutions, where the real is so close ;-)
Andreas

How to inheritance a super class without no-argument constructor

i try to inheritance javax.swing.tree.DefaultTreeModel:
public class myTreeModel extends DefaultTreeModel
but the compiler say:
'constructor DefaultTreeModel() not found in class javax.swing.tree.DefaultTreeModel'
and stoped.
How can I get around this?
THANK YOU for your consideration.

Inside myTreeModel, i tried several things:
1. add a no-argument constructor;
Your no argument constructor should be either one of the below :
public myTreeModel() {
   super(new DefaultMutableTreeNode());
public myTreeModel() {
   super(new DefaultMutableTreeNode(), true);
2. add a contructor with (DefaultTreeNode) argument;
Your constructor with tree node argument should be either one of the below :
public myTreeModel(DefaultMutableTreeNode node) {
   super(node);
public myTreeModel(DefaultMutableTreeNode node) {
   super(node, true);
}You would get an error if you did the following:
public myTreeModel() {
public myTreeModel(DefaultMutableTreeNode node) {
}In both of the cases the default no arguement constructor of the super class is called implicitly like:
public myTreeModel() {
   super();
public myTreeModel(DefaultMutableTreeNode node) {
   super();
}In this case the call super() is refering to a no arguement constructor in DefaultTreeModel. However, no such constructor exists in the DefaultTreeModel class resulting in a compile time error.
Note: You do not need to use DefaultMutableTreeNode. You an use some other class that implements the TreeNode interface.

Is it possible to OVERLOAD a super-class method in a sub-class?

Hi all,
I have a query that
Is it possible to OVERLOAD a super-class method in a sub-class?
If it is possible, please give me an example.
Thanks,
Hari

Hi,
Is the method int Display(int a){} overloading
the super-class's void Display() method? If
possible, please clarify this and how it would be
method overloading?
hanks,
Hari
Hi Hari,
Yes, it is possible. Look at this piece of code:
class Senior
     void Display()
          System.out.println("Super class method");
class Junior extends Senior
     int Display(int a)
          System.out.println("Subclass method: "+a);
          return(a+10);
     }> }
class example
     public static void main(String args[])
          Junior j = new Junior();
          j.Display();
System.out.println("Subclass method
od "+j.Display(5));
Is this what you were asking? Hope this helped.Hi,
I guess you guys are confused here...
Overloading is achieved by methods in the same class...
Overriding is across a superclass subclass methds.

Servicegen for sub-class inside vector variable of Super

java.lang.NoSuchMethodError
at com.netsboss.WSBE.model.QueryItemCodec.typedInvokeGetter(QueryItemCod
ec.java:87)
at com.netsboss.WSBE.model.QueryItemCodec.invokeGetter(QueryItemCodec.ja
va:56)
at weblogic.xml.schema.binding.BeanCodecBase.gatherContents(BeanCodecBas
e.java:295)
at weblogic.xml.schema.binding.CodecBase.serializeFill(CodecBase.java:25
3)
at weblogic.xml.schema.binding.CodecBase.serialize(CodecBase.java:195)
at weblogic.xml.schema.binding.RuntimeUtils.invoke_serializer(RuntimeUti
ls.java:184)loop
at weblogic.xml.schema.binding.RuntimeUtils.invoke_serializer(RuntimeUti
ls.java:170)
QueryItem {
private Vector airItiners;
public Vector getAirItiners() {
return airItiners;
public class AirItinerary implements Serializable{}
QueryItem is my return class. The return result will include sub class AirItinerary
in QueryItem's Vector. I notice servicegen will only generate stub and web.xml
for QueryItem.
I get above error, when the result return to client. How to generate necessary
sub-class inside a vector variable of Super class?
Stephen

Hi Stephen,
write my own ser/deser? Any other quick way?Our excellent support group ([email protected]) may be able to help with
an alternative solution. If you could create a small reproducer, then
this will help them with a clear picture of your goal.
One more problem, wls deloy my WSBE.ear as a war correctly. But error show noDouble check the console log for any messages. Also try:
http://[host]:[port]/[contextURI]/[serviceURI]
See: http://edocs.bea.com/wls/docs70/webserv/client.html#1051033 and
also check the console to verify the app is or is not deployed. See:
http://edocs.bea.com/wls/docs70/programming/deploying.html
HTHs,
Bruce
Stephen Zeng wrote:
>
Hi Bruce:
Our company use wsl7.0. We are not able to update to wls8 in this project. Do
I have to
write my own ser/deser? Any other quick way?
sub class variable:
public class AirItinerary implements Serializable{
private String air;
private Vector flightItem; //sub class of AirItineray
One more problem, wls deloy my WSBE.ear as a war correctly. But error show no
deloyment found. web-services.xml has been generated by servicegen under web-inf
path. Thanks Bruce.
Stephen
Bruce Stephens <[email protected]> wrote:
Hi Stephen,
The java.util.vector should be converted to a SOAP Array, see:
http://edocs.bea.com/wls/docs81/webserv/assemble.html#1060696 however
the issue of the sub-class is most likely the problem. Can you simplify
the data types? You may just have to write your own ser/deser, see:
http://edocs.bea.com/wls/docs81/webserv/customdata.html#1060764
This is with WLS 8.1, right?
Thanks,
Bruce
Stephen Zeng wrote:
java.lang.NoSuchMethodError
at com.netsboss.WSBE.model.QueryItemCodec.typedInvokeGetter(QueryItemCod
ec.java:87)
at com.netsboss.WSBE.model.QueryItemCodec.invokeGetter(QueryItemCodec.ja
va:56)
at weblogic.xml.schema.binding.BeanCodecBase.gatherContents(BeanCodecBas
e.java:295)
at weblogic.xml.schema.binding.CodecBase.serializeFill(CodecBase.java:25
3)
at weblogic.xml.schema.binding.CodecBase.serialize(CodecBase.java:195)
at weblogic.xml.schema.binding.RuntimeUtils.invoke_serializer(RuntimeUti
ls.java:184)loop
at weblogic.xml.schema.binding.RuntimeUtils.invoke_serializer(RuntimeUti
ls.java:170)
QueryItem {
private Vector airItiners;
public Vector getAirItiners() {
return airItiners;
public class AirItinerary implements Serializable{}
QueryItem is my return class. The return result will include sub classAirItinerary
in QueryItem's Vector. I notice servicegen will only generate stuband web.xml
for QueryItem.
I get above error, when the result return to client. How to generatenecessary
sub-class inside a vector variable of Super class?
Stephen

Can we chagne Super class method parameters in Sub class

Hi,
I created a super class. In that class i created a method. That method is having 4 input parameters and 4 export parameters.
I created a sub class for that super class. I need to use only 2 input parameters in this class rather than 4 parameters. I want to delete 2 Input parameters in the sub class of the super class method. Is it possible.
If possible. can we give an simple code or pseudo code?
regards,
krishna

Hi,
I think you can not.
Because, only public attributes can be inherited and they will remain public in the subclass.
for further detail check,
http://help.sap.com/saphelp_nw70/helpdata/en/1d/df5f57127111d3b9390000e8353423/content.htm
regards,
Anirban

Calling sub class method from superclass constructure

hi all
i have seen a program in which a super class constructure class methods of sub class before initialization of fields in subclass ,i want how this is posibble ?
thanks in advance

Hear is the code n other thing i have used final variable without initialization n compiler dosen't report error
abstract class Test
public Test()
System.out.println("In DemoClass Constructer");
this.show();
public void show()
System.out.println("In DemoClass Show() method");
class Sub1 extends Test
private final float number;
public Sub1(float n)
this.number=n;
System.out.println((new StringBuilder()).append("Number is==").append(number).toString());
int j;
public void show()
System.out.println("In Sub1 Class Show method ");
public class DemoClass
public static void main(String s[])
Sub1 obj1=new Sub1(5);
Sub1 obj2=new Sub1(6);
thanks for reply

Can we change the Super class attribute scope in Sub class

Hi.
I created a super class. In that i have 4 attributes. That attributes are PUBLIC.
I created a sub class. In that i got all super class attributes. I want to change that attributes as a Private. Is it possible.
If it is possible.Give me an Example with code or Pseudo code.
Regards.
Krishna.

Hi Krishna,
It is not possible... If you declare the Attributes again in Subclass of the same name as that of Super class
then the way of accessing them would be different from that of attributes in the main class.
Hope this would help you
Good luck
Narin

Why the constructor of the base class calls first when u run the java app.

why the constructor of the base class calls first when u run the java application

For the record the other very exciting questions are:
pls give the differences between application server and web server with examples
will u pls narrate the differences between servlet context and servlet config.....
where can we find servlet config...
is there any methods to access servlet config

Super and sub classes

Using an Super class and couple of subclasses of this super.
Super{
m1(){
subclass1, subclass2, subclass3...etc.
these subclasses call super class method m1().
In super class m1() want to know which subclass called this method m1(). how to find this?
Ofcourse can use a variable and in super and set it in subclass but is there a smart way in java to find this. I would appreciate your help.
Thanks.

if (this instanceof SuperClass)
if (this instanceof SubClass1)
etc.
But this is very poor design. You should override m1() in each subclass to have it do whatever is necessary in each case.

Sub class calls super in constructor

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