How To Maintain List Of Static Class And Instantiate From It
Feb 26, 2015
I have a list of uninstanciated class types and I wanted to call a static function from these "Class<? extends PropControl>" (without using reflection) that would create a new corresponding object instance but it appears I cant do that in java so now I want to create a factory that takes a class type as aparameter to create the corresponding object instance but this code dont compile:
Java Code:
public PropControl Create(Class<? extends PropControl> cls)
{
if(cls==HouseControl.class) <---- ERROR
{
here I create a new instance of HouseControl (that inherits PropControl)
}
} mh_sh_highlight_all('java');
I get this error :
incomparable types: Class<CAP#1> and Class<HouseControl>
where CAP#1 is a fresh type-variable:
CAP#1 extends PropControl from capture of ? extends PropControl
I am stuck on what to put in my functions for this question: Write a program to maintain a list of the high scores obtained in a game. The program should first ask the user how many scores they want to maintain and then repeatedly accept new scores from the user and should add the score to the list of high scores (in the appropriate position) if it is higher than any of the existing high scores. You must include the following functions:
-initialiseHighScores () which sets all high scores to zero.
-printHighScores() which prints the high scores in the format: "The high scores are 345, 300, 234", for all exisiting high scores in the list (remember that sometimes it won't be full).
-higherThan() which takes the high scores and a new score and returns whether the passed score is higher than any of those in the high score list.
-insertScore() which takes the current high score list and a new score and updates it by inserting the new score at the appropriate position in the list
here are my functions the insertScore is missing because I am having troubles with it.
public static void initialiseHighScores (int[] scores, int size) { for (int i = 0; i < size; i++) { scores [i] = 0; } } public static boolean higherThan (int[] scores, int size, int newScore) {
I have a quick polymorphism question. I have a parent class and a sub class that extends the parent class. I then declare an array of parent class but instantiate an index to the sub class using polymorphism. Do I have to have all the same methods in the child class that I do in the parent class? Here is an example of what I mean.
public class ParentClass { public ParentClass(....){ } public String doSomething(){ } } public class ChildClass extends ParentClass { public ChildClass(....)
[Code] ....
Is polymorphism similar to interfaces where the child class needs all the same methods?
Currently my application is on Tomcat5.0.16.I use struts1.2, jstl 1.1 , jsp-api 2.0.I tried to migrate my application from tomcat5.0 to tomcat 6.0.26.I didn't see any issue in deployment but when i tried to access jsp pages i got this exception.
HTTP Status 500 -
type Exception report
message
description The server encountered an internal error () that prevented it from fulfilling this request.
exception
org.apache.jasper.JasperException: /pbuilder/login/legacyLogin.jsp(6,4) Failed to load or instantiate TagLibraryValidator class: org.apache.taglibs.standard.tlv.JstlCoreTLV org.apache.jasper.compiler.DefaultErrorHandler.jspError(DefaultErrorHandler.java:40) org.apache.jasper.compiler.ErrorDispatcher.dispatch(ErrorDispatcher.java:407) org.apache.jasper.compiler.ErrorDispatcher.jspError(ErrorDispatcher.java:88) org.apache.jasper.compiler.Parser.processIncludeDirective(Parser.java:297)
[code]....
i found that jstl1.1 jar didn't have the above mentioned class.I replaced jstl1.1 with jstl1.2 jar.i verified that jstl1.2 jar had JstlCoreTLV calss.but even after this replacement of jar i am facing the same issue.
I currently use Eclipse to maintain our Java application. I recently upgraded from Java 6 to Java 7. I updated my Eclipse projects to use the Java 7 .jar files. I can run the application from Eclipse via the Run Configuration.
I can also run the Ant build and it completes successfully. When I install the application on my desktop, I receive the "Java Virtual Machine Launcher: Could not find main class..." error. My CLASSPATH is set to ".".
From what i understand static methods should be called without creating an instance of the same class . If so why would they return an instance of the same class like in the following : public static Location locateLargest(double[][] a) , the Location class being the same class where the method is defined . I don't understand this , does it mean that every field and every method in the class must be static ? Meaning that you cannot have instances of the class because everything is static . Or it's just a mistake and the class Location cannot have a static method: public static Location locateLargest(double[][] a) ?
This is a someway special question, because I am using jmonkeyEngine.
But the topic is simple:
I have 2 classes:
public class Spielbrett extends SimpleApplication { public static void main(String[] args) { Spielbrett app = new Spielbrett(); app.start(); } @Override public void simpleInitApp() {
[Code]...
as the main class and a second class for the chips:
public class Spielstein { public Spatial stone; public int player; public int team; private AssetManager assetManager = Spielstein.getAM(); //THIS IS THE PROBLEM public Spielstein(int t_player, int t_team){
[Code]...
My problem is: I can't access getAM() from the first in the second class. If you know why I would be glad for an answer.
I have this ListInterface class that has operations for my linked list and a LList class. The Llist and ListInterface classes are perfect. My job is to create a driver, or a demo class that showcases these operations. That being said, heres the driver so far:
import java.util.*; public abstract class DriverWilson implements ListInterface { public static void main(String[] args) {
I’m trying to understand how to decide when to make a nested class static or non-static. These are my assumptions.
1) Make a nested class static if each instance of its enclosing class may have one or more instances of its nested class, for example, a HashMap has a static HashMap.Entry nested class because each HashMap instance may have one or more HashMap.Entry instances
2) Make a nested class non-static if each instance of its enclosing class must have only one instance of its nested class, for example, an AbstractButton has a non-static AbstractButton.Handler nested class because each AbstractButton instance must have only one AbstractButton.Handler instance.
I wrote a code to use static class. But, when I call the class in a outer class but, it gives an error. Is it mandatory to have a static class should have static variables when we declaring them??
public class StaticClassMain { static class Sub{ String str="Example 1"; } public static void main(String[] args) { System.out.println(Sub.str); } }
I have a fixed list of 20+ values to be populated in a dropdown. The set of values are always going to remain the same, no future scope of modifications, additions or deletions.
Listing each of them as <option> in JSP is making the page look cluttered. Or is it better reading it as a comma-separated string from a properties file and then iterating to populate the dropdown.
What will be the best approach to populate such a dropdown in JSP?
I am working on a project involving a class that has the attributes of one of its inner classes. Now, if possible, I would like to make it so that the inner class is not visible outside of the class. Also, some of the functional mechanics require that the class be an instance of the nested inner class (it extends the inner class). The following code snippet demonstrates the situation.
public class A extends A.B { public static class B { //ideally I would like this to be private/protected. } }
When I try to compile this program, I get the error message "Cyclical inheritance involving A." This error does not make much sense because, since the inner class "B" is static, it requires no instance of "A" (it does not inherit from "A" or uses it). My question is "Is it possible to do something similar to this structure?" I have searched many forums in search of the answer but have not found anything that attempts to explain it. The closest problem that I have found is one relating to the inheritance of a nested inner class from another class. I would like to express that the problem that I am having involves a class defined within the inheriting class.
I have an Abstract Class called GameColorEffect which contains a number of non-static Inner Classes that extend their Parent Class, GameColorEffect. I want to be able to create instances of the Inner Classes, however my IDE, eclipse, prompts me with the error:
No enclosing instance of type GameColorEffect is accessible. Must qualify the allocation with an enclosing instance of type GameColorEffect
And eclipse shows me a possible solution which is to turn the Inner Classes to static, this would allow me to create instances, but not really. This is because using methods from the static Inner Classes that change values in the Inner Classes will do this for every instance of the same Inner Class which is literally like a single instance. However, I want these Inner Classes to be individual with their values and still be able to use them outside as instances. I've found out a possible solution, which I'm not sure works like I want it to:
Java Code : GameColorEffect = new GameColorEffect.ExampleEffect(); mh_sh_highlight_all('java');
However, this is in-compact because sometimes all I need is to use just a method like:
Java Code : new GameColorEffect.ExampleEffect(intensity).applyEffect() mh_sh_highlight_all('java');
And another solution that I already knew prior was that I could make the Inner Classes proper classes not inside of the GameColorEffect class, but this is also in-compact because I will have to have so many classes for the so many effects that I have.
I have a class Tree in which all the methods to build a tree are in place. But however I would want variable of by Tree which is pointing to the last node being added to the tree.
So basically every time you keep adding a node to the tree you tail pointer gets updated to point to the last node. I have this so far.
public class NonEmptyTree implements Tree { private Tree left; private int data; private int leftleafCount; private int rightleafCount; private Tree right; private Tree tail; // This variable must be shared by all the object. There needs to just one tail pointer to the tree. public Tree insert( data ) { tail = // gets updated every time when new node gets added.
Sandwich class. I have thus far completed creating a sandwich class with a seperate sandwich Tester class to run with it. (this is according to the assignment). Now I must create Static variables for the sandwich class:
Add two static variables to the Sandwich class to count how many sandwiches are sold and how many slices of tomato are used. Initialize each to 0.Where do you add code to increment the sandwich counter? Determine this and then add code.
public class Sandwich { static int numOfSold = 0; static int slicesUsed = 0; private String meat; private int numOfSlicesOfTomato; private boolean lettuce;
I am getting an error trying to access a static method of another class...theyre both in the same package, I've tried importing the class.
I've tried to do A b=new A() and then b.evaluate();
Everything that I try I get the following error:
Exception in thread "main" java.lang.NoClassDefFoundError: B$A Caused by: java.lang.ClassNotFoundException: B$A at java.net.URLClassLoader$1.run(URLClassLoader.java:202) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:306) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Code :
public class A{ public static String evaluate(String op) { } } public class B{ String output=A.evaluate(input); }
A common solution to this problem is to write a utility class whose responsibility is to log information. This class can have a flag that will allow you to turn the logging on and off. In addition you should be able to tell the class how much detail you want in the output. Ultimately, this class will give you the ability to control when information is logged, what information is logged, how often information is logged, and even where the information is logged. And you would be able to control all of this without changing a single line of code!
This type of utility class is commonly written using static methods and is referred to as a static class. In order to use the features of a utility class, the application can access the methods directly by referring the class name, eliminating the need to create an instance of the class in order to execute the methods.
import java.util.Arrays; import java.util.Comparator; class SimpleHolder extends Object { private final int value; public SimpleHolder(int value) { this.value = value;
[Code] ....
According to The Java Tutorial, static nested classes should not have access to other members of the enclosing class. I'd suppose to get compile-time error in the BasicComparator class. However, my code compiles just fine. Am I missing something?
