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 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 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 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>()
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)
Regarding the lifecycle of servlet , in headfirst servlet i can find :
You normally will NOT override the service() method, so the one from HttpServlet will run. The service() method figures out which HTTP method (GET, POST, etc.) is in the request, and invokes the matching doGet() or doPost() method. The doGet() and doPost() inside HttpServlet don’t do anything, so you have to override one or both. This thread dies (or is put back in a Container-managed pool) when service() completes.
How can I call the doGet method of the subclass from the superclass. i am not getting this .
I am very new to Java Swing. I have to create a TreeTable in Java Swing with a Parent Row having say 6 columns and its all child row having just 4 columns. like shown below
I've a parent class with a argument constructor like below(a sample code)
public class Parent { Parent(String name) { System.out.println(name); } public static void main(String[] args) { } }
Also I've child.class which extends Parent.class as shown below,
public class child extends Parent { child(String name) { super(name); } }
Now, I want create/modify the constructor which is in child, by taking "int i" as an input instead of "String name". How can I do that? Run time I want to execute child constructor not a parent constructor.
Condition is: Without making any changes to the Parent class
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 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 two classes (Daughter and Son) that contain some very similar method definitions:
public class Family { public static void main(String[] args) { Daughter d = new Daughter(); Son s = new Son(); d.speak(); s.speak();
[Code] .....
Each of those classes has a "speak" method with two out of three lines being identical. I could move those into a parent class, but I need each of the child classes to continue to exhibit its unique behavior. I'm trying the approach below, which replaces the unique code with a call to a "placeholder" method that must be implemented by each child class:
public class Family { public static void main(String[] args) { Daughter d = new Daughter(); Son s = new Son();
[Code] .....
This works and moves the shared code from two places (the Daughter and Son classes) into one place (the new Mother class, which is now a parent class of Daughter and Son). Something about this feels a bit odd to me, though. It's one thing for a child class to override a parent class's methods to extend or alter their behavior. But, here, I've implemented an abstract method in the parent class to alter what happens when the parent class's method (speak(), in this case) is called, without overriding that parent class method itself.
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'm working on a simple 2D Game Framework. Currently it's creating a window, but I'm working on an update method.
I constantly export the framework as a .jar file, and I've added it to the game's build path (using eclipse). I wonder if I can check all classes in the game-project (the project in which I've refecrenced the Framework in) for a specific method (for example update()) and call all found methods with that name from the framework's main class, like this:
public class FrameworkClass1 { private void checkForUpdateMethods() { // Check for update methods on program start } public void update() { runAllFoundUpdateMethods(); // Run all update methods found in the scan } }
I want to do this because it would be a simple way to update and render the game. If the main game-class look something like this:
public class Game { public void update() { // Update the game every time this is ran } }
it will be automatically updated, because it contains a method named update(), instead of naming the main game-class with a specific name etc. It will simply be more flexible that way!
I was reading the book, "Head First Java" and it was talking about how there may be multiple classes in a large application, but there will be only one main method.how does it work that way? How can you have multiple classes, but only one main method?
My current assignment involves me outputting these 2 classes. Yet I'm not really sure in what manner I should go about doing this. I have tried creating a separate class and outputting my toString methods there but for some reason I am getting an error. .
The error message is thus;
Exception in thread "main" java.lang.NullPointerException at Vehicle.toString(Vehicle.java:91) at Run.main(Run.java:17) Process completed.
class Test3 { } class MySub extends Test3 { } class Test4{ public static void main(String args[]) { MySub m = new MySub(); } }
I learned that if a class and its parent class both have no constructors, the compiler is supposed to complain. When I compiled Test4, i got no errors. why did it give no errors?
I'm working on a program using GUI. My problem is that I'm reaching **1000 Line** and this is stressful because all my code are in one file. I'm not liking this. So I research the internet about Inheritance. However, what I know about Inheritance that Inherit everything in the parent class. However, when I try to use a variables in the child class to override it in the parent class I can't for example let say that I have in the parent class something like this:
JButton getButton = new JButton("Enter");
Now when I go to the child class. I want to Inherit and use this variable so I can use the ActionListener on the getButton and override for the parent class, but it's not working.
This is my code:
public class H_Store extends JFrame { private String s ="Kinds: "; private JButton calculateButton; private JPanel mainPane; private JPanel getProfitPanel; private JTextField ground_M_QTextField;
[Code] ....
What I want to do exactly is to take the last code into another class or do something with it so I can use it in the Parent class, in other word any math calculation method or class I want them outside the Parent class. I mean this code :
private class CalcButtonListener implements ActionListener{ // vairbles for the ground Meat check box private double total_GM; private double weightPrice_1; private String stringQ; private String stringW; private String stringP;
We created one web application which runs on tomcat 7.0.35 using spring mvc 3.0 . Its working perfectly on 32-bit windows machine in IE 8 on Windows 7 OS, when we tried to run this on 64-bit windows 2008 Server, jquery is not working. Also I populate data from Pop-up JSP to parent JSP, and it works 3/10 times only and does not work always.
We used the following jquery plugins in our project
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?
