I understand how to write a child object. I know what can access what and the order of execution of each statement, including fields, initialization blocks, and constructors. I know what will be inherited by the child and how private fields and methods are not inherited. I also know that private fields and methods in Parent are still accessible indirectly through constructors, and non-private methods. I know how to use super() and this() with or without parameters. I know when super() will be automatically inserted by the compiler and how the Object class will always be the ultimate parent class. However, I have not been able to find an explanation of exactly (or even approximately) how all this is actually put together into an actual object in memory.
For instance, if Parent.field is private and Parent.fieldGetter() is public then Child inherits fieldGetter() and can call it directly as if it is a member of Child. In fact other classes can call Child.fieldGetter() with no clue that it is not an actual member of Child. But, if fieldGetter() is now part of Child and Parent was never actually instantiated, then how is Parent.field available for Child.fieldGetter() to read? In fact, how does Parent.field exist at all? Where is it stored? (OK, I know, "on the heap.") But I want to know what it is associated with in memory. Is it treated like part of Child? Is there really a Parent object on the heap and Child simply contains references to the parts of Parent that it inherited? What?
Below mentioned classes, create object system accept in both way so what is it significant.
============ ABC obj = new Test();
Test obj = new Test(); ==================
--file ABC class
class ABC{ public void disp() { System.out.println("disp() method of parent class"); } public void abc() { System.out.println("abc() method of parent class"); } }
--file Test class
class Test extends ABC{ public void disp(){ System.out.println("disp() method of Child class"); } public void xyz(){ System.out.println("xyz() method of Child class"); } public static void main( String args[]) { //Parent class reference to child class object ABC obj = new Test(); obj.disp(); obj.abc(); }}
I want to know is there any way we can call parent class method using child class object without using super keyword in class B in the following program like we can do in c++ by using scoop resolution operator
class A{ public void hello(){ System.out.println("hello"); } } class B extends A{ public void hello(){ //super.hello(); System.out.println("hello1");
I'm trying to fill a List<String>, named overlappedGrid, from another List<String>, named listGrid. I'm facing an exception:Exception in thread "main" java.lang.RuntimeException: Uncompilable source code - unexpected type
required: variable found: value at arab2004_d.ProcessingLayer.printShape(Arab2004_D.j ava:101) at arab2004_d.Arab2004_D.main(Arab2004_D.java:30)
Java Result: 1
Here is my source code (the exception line is commented "here is the exception"):
I keep getting an error every time saying there is no main class ...
Loan
public class Loan implements LoanConstant{ public static int loanNumber; public static String lastName; public static int loanAmount; public static int interestRate; public static int term; public int primRate;
public class User implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) @Column(unique = true, nullable = false) private int id;
public List<UserReason> getUserReasons() { return userReasons; } public void setUserReasons(List<UserReason> userReasons) { this.userReasons = userReasons; }
public UserReason addUserReason(UserReason userReason) { if (userReasons == null) { userReasons = new ArrayList<UserReason>();
[Code] ....
I want to be able to add userReason to the list, and that Hibernate will automatically update the reference between the parent & child object.
When using the above code, when trying to start the server, i'm getting the error message:
Repeated column in mapping for entity: com.commit.safebeyond.model.UserReason column: userId (should be mapped with insert="false" update="false")
Please notice that i mapped the userId in UserReasonPK with insertable = false, updatable = false.
If i change it, and add this on the User property in UserReason object, server is up, but when trying to insert new User I'm getting the following error:
I want to make an application and must use strategy pattern my idea is to create a super class in this case Movie Player and three sub classer and they'll komminesera with each other using strattegy pattern, one of the sub classes is Button Panel and I want to add it to Movie Player and it was to be its child,so how can I add the butt panel to Movie Player and it shall be its children?
I keep hearing these two term when it comes to painting in Swing, however, I'm not sure which is which. To my understanding is that the child components are the ones that already exist on screen (could be a JButton, JFrame, or custom painting) . and the parent components are the one to be added/drawn next. (hence, if we override the paintChildren() method when painting, the components that were already on the screen don't appear any more).
I can call a child method from a main method. If I have a parent called "Assessment", a child called "Quiz", and another child called "test". Can I instantiate an object like Assessment a = new test(); and call a method in test.
I know the method can be called if I instantiate the test t = new test() but that defeats the purpose of inheritance...
i have created two(displaypanel & buttonpanel) main panels in a JFrame and many child panels,one of the panel is for holding buttons and displaypanel mainly swap child panel as directed from buttonpanel, but the problem arises i cannot navigate from child panel to another child panel,
as i have made a button on one of a child panel and from button panel i add the childpanel to displaypanel.it is working but when i tried to navigate from the button which is on child panel nothing happened. "i have made a function in main form which swap the content of mainpanel (displaypanel) and in childpanel i have acces the function through object of mainform"
I can call a child method from a main method. If I have a parent called "Assessment", a child called "Quiz", and another child called "test". Can I instinate an object like Assessment a = new test(); and call a method in test.I know the method can be called if I instinate the test t = new test() but that defeats the purpose of inheritance which I'm learning in class.
I have been working on a simple problem, but I am stuck. I am trying to learn parent and child classes and how they work. The program in broken into three classes; the DemoBook class that runs the various methods, the Book class that gathers information and displays it, and finally a child class of Book (called TextBook) that just gets one piece of data and then is suppossed to return that data back to Book. However, this is not working and I know I am missing something; I believe it has to do with Set and Get methods, but I am confused with how these work.
Java Code:
public class DemoBook { public static void main (String[] args) { Book aBook = new Book(); Textbook aText = new Textbook();
I am creating a commenting system for a side project of mine I'm building using AnuglarJS for the front-end and Spring MVC for the backend.
I am having difficulty coming up with an algorithm that will populate each comment object with a list of the comments that are responses/children of it.
The below code is what I have so far. The problem is is that it duplicates comments.
public List<Comment> getComments(int id) { MapSqlParameterSource params = new MapSqlParameterSource(); params.addValue("id", id); List<Comment> allComments = jdbc.query("select * from comments where debate_id=:id", params, new RowMapper<Comment>()
Everything is working fine but in my case One customer has Many orders but when i do customer.getOrders() the child objects are not loading . I dont know why.am i missing something here im using MYSQL database
I am working with a program where I am required to use a JFrame in a child class. The only way that I know how to access a JFrame is to do, example (public class Example extends JFrame), but since it is already extending the parent class, I am kind of stuck. I do not think that you can extend two separate classes, so..... I am stuck.
If I lets say have an interface Animal, and I create a lot of classes with a different animal name that implement the interface Animal. Then I create an ArrayList of Animal. Then I would put in lets say Dog class into the ArrayList, which has custom methods and data that the Animal Interface doesn't have, is this data ripped away except for the methods that are put in the Animal interface? So if I would cast the Animal back to Dog, would it retain all the data that existed before it was placed in the ArrayList?
I keep hearing these two term when it comes to painting in Swing, however, I'm not sure which is which. To my understanding is that the child components are the ones that already exist on screen (could be a JButton, JFrame, or custom painting) . and the parent components are the one to be added/drawn next. (hence, if we override the paintChildren() method when painting, the components that were already on the screen don't appear any more) ....
The company entity contains companyName, Sector and Segment columns. The mapping is 3 entities (Company, Sector, Segment) where Sector and Segment are used to create a company record. Sector has a OneToMany relationship with Segment and with Company. I put the Sector and Segment values into two select menus as use these to create a Sector and Segment reference for the Company table. I'm getting the following exception:
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`testdummy`.`company`, CONSTRAINT `FK_COMPANY_FK_COMPANY_SECTORID` FOREIGN KEY (`FK_COMPANY_SECTORID`) REFERENCES `sectors` (`SECTORID`)) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
I'm thinking that the problem is that since the Segment entity is a child of Sector it must be entered through an instance of Sector. Because it's being entered as a separate value I'm getting this error. The problem is Segment is defined as a Set in the Sector entity and I can't figure out how to declare Segment as an instance using its parent entity (Sector).
My code is as follows, starting with the Sector entity:
@Entity @Table(name = "SECTORSNEW") public class SectorsNew { @Id @GeneratedValue(strategy = GenerationType.AUTO) private int sectorId; private String sectorName; @OneToMany(cascade = CascadeType.PERSIST)
I found the following inheritance and encapsulation issue . Suppose you have a parent class with a non-static protected attribute.
package package1; public class Parent{ protected int a = 10; // this is the non-static protected attribute in question public static void main(String args[]){ // whatever logic }// end Parent class }// end main()
Now suppose you have a child class in another package and you have imported in the parent class.
package package2; import package1.Parent; public class Child extends Parent{ public static void main(String[] args){ Parent p = new Parent(); Child c = new Child();
System.out.println(p.a); //should print out 10 BUT DOES NOT System.out.println(c.a); //should print out 10 }// end main() }// end Child class
My observation is that p.a produces an error even though, to the best of my knowledge, it should not. I believe the statement "System.out.println(p.a);" should print out a 10.
Am I misunderstanding something about inheritance and encapsulation?
I have a project I am currently working on using Primefaces and MySQL. I have a page that will display information queried from the database. I have textfields that will display the data from a given record. But I want to ensure that the displayed data cannot be altered. I decided on disabling the textfields unless the create or edit button were clicked. At which point all textfields will be enabled for editing, and cleared if create button was clicked. I want to push the disabling/enabling of the elements back to a managed bean, but I want to have the bean take in two lists or arrays, one containing all elements by ID and one containing a list of exempt elements. Is there a way I can create a List or Array of the ID's that I can send to the bean? I know little in Javascript and previous attempts to implement it have met with little success.
I want to create a list that would contain all and another that would contain the exemptions such as searchField, searchCriteria, searchButton, projectList and viewButton. The actual exemption list is far smaller than the list of all children. I have found sources that can disable the elements with a java bean, but I have not been able to find one that would allow me to define those that should and should not be disabled, then vice versa for enabling.
As you can see instead of displaying the champion name it is displaying the memory location and I do not know how to fix it.
class Champions { String name; Champions [] weak = new Champions [3]; Champions [] strong = new Champions [3]; String [] items = new String [3]; public static void main (String [] args) {
For some reason my code returns the memory address of the array when its a print statement with a string, but it works fine when its in a separate print statement all by itself. Why? Do I need to create a toString method that converts a char array to a String to something? The reason why I ask that is becuase on Eclipse line 10 has a warning stating "Must explicitly convert char[] to a String".
public class Ex { private String word; public Ex(String word) { this.word = word; } public char[] Display(){ char[] wordChars = this.word.toCharArray(); return wordChars;
[Code] .....
Result:
Hello world The word is: [C@1db9742
I also tried this, knowing that it's a long shot, but that didnt do anything...
public String toString(){ Ex ex = new Ex(this.word); char[] word = ex.Display(); String updated = word.toString();//counter intuitive? return updated; }
So I have that traditional memory game homework assignment and for some reason I can't figure out how to put the codes in order. I can't figure out the arrangement to make it work. So far I have
import java.util.Random; import java.util.Scanner; public class MemoryGame {
