JComboBox Should Be Used In A Generic Manner
Sep 9, 2014
I recently posted that JComboBox should be used in a generic manner. I presumed that once declared, with some type Foo, that one could then do:
Java Code:
JComboxBox<Foo> cb = new JComboBox<>();
// sometime later
Foo foo = cb.getSelectedItem(); mh_sh_highlight_all('java');
However, getSelectedItem() is documented to return a type of Object so a cast is still needed. I can't understand (even for backward compatibility) why it doesn't return a type of the specified type. Many other old classes have been converted to generics so why should this be any different? I just found that one could use getPrototypeDisplayValue() but that seems counter intuitive.
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Jul 23, 2014
1 import java.util.ArrayList;
2 import java.util.List;
3
4 public class MyList<E> {
5
6 public List<E> list;
7 public int length;
[code]...
I am trying to define a class MyList, which i just a wrapper around an ArrayList, no real purpose, just for the sake of learning Generics. Idea here is that I create a parameterized class, MyList<E>, which holds a parameterized instance var of type List<E>. I have an add method which adds an element of type E to the List<E>. If I create an instance of MyList, call it 'm', for some reason when I try to call a method on that instance the compiler complains that 'm' cannot be found.
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Apr 15, 2014
Trying to implement PageRank in a naive manner with graph nodes as pages and subsequent calculations. Correcting the code.
import java.util.*;
import java.io.*;
class PageRank {
public static void main(String args[]) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter no.of pages");
int n=sc.nextInt();
[Code] .....
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Oct 7, 2014
I've implemented Stack on the base of the LinkedList. It works as i expect it to work, but then i tried to made it compatible with foreach loop. I've implemented Iterable and Iterator. Code compiles and works fine, but does not return any output. It looks like while working with foreach, next() is not called at all. If i`m getting iterator from instance and try to do iterator.next(), i get output as expected.
public class genericStack<T> implements Iterator<T>, Iterable<T> {
private LinkedList<T> LL ;
protected genericStack() {
this.LL = new LinkedList<T>();
}
public static void main(String[] args) {
[Code] ....
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Feb 28, 2014
Trying to make a universal tool for increment an array by one while keeping all the previous values in place.
public K[] increment(K[] k){
int i = 0;
K[] tmp = (K[])new Object[Array.getLength(k)+1];
/*
* Parses through the passed k and fills tmp with all of ks values
[code]...
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Apr 1, 2014
I am trying to understand the concept of Generics in java. In the introduction to Generic Types, this example is given:
Java Code: public class Box {
private Object object;
public void set(Object object) { this.object = object; }
public Object get() { return object; }
} mh_sh_highlight_all('java'); "Since
Since its methods accept or return an Object, you are free to pass in whatever you want, provided that it is not one of the primitive types." - I understand this.But then it has been changed to a generic class:
Java Code: /**
* Generic version of the Box class.
* @param <T> the type of the value being boxed
*/
public class Box<T> {
// T stands for "Type"
private T t;
public void set(T t) { this.t = t; }
public T get() { return t; }
} mh_sh_highlight_all('java'); "
As you can see, all occurrences of Object are replaced by T. A type variable can be any non-primitive type you specify: any class type, any interface type, any array type, or even another type variable."We can use any type in place of an Object, because Object is a superclass of all classes. But T (or any other class) is not a superclass of all classes. So how do we justify any class being used in place of a random T or any other class?
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Aug 5, 2014
I'm wondering if there's a way to build a template for managed beans which could be extended by a constructor instead of re-writing beans for each entity. I can do that quite easily for Dao objects by creating facades and using those facades to create Dao implementations for specific entities. Not sure if the same concept works for managed beans and haven't really come accross any searches.
I wrote the following but I'm not sure how to implement or even if the concept of generics and templating can be applied to managed beans in the same way it can be applied to Dao classes:
public class BeanTemplate<T> {
private ListDataModel<T> listModel;
@EJB
private GenDao dao;
private Class<T> entityClass;
[Code] .....
The above assumes there's only one method needed in the bean. I thought of extending like this:
public class EmployeeBean extends BeanTemplate<Employee> {
public EmployeeBean() {
super(Employee.class);
}
// how can the methods be called??
Is the same concept for creating dao templates possible for managed beans?
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Oct 3, 2014
I am working on a java program that is called OrderedVector which is basically a storage or list that grows and shrinks depending on the amount of data is put in. Most of the methods in my code are correct and working, the only real issue I have lies with either the remove(E obj) method or remove(int index) method. This is the driver I am currently using to test my remove method,
public class Tester {
public static void main(String[] args) {
OrderedListADT<Integer> v;
v = new OrderedVector<Integer>();
for(int i = 0 ; i <= 9; i++){
v.insert(i);
[code]....
the output I am receiving is
Removing 0
Size of data structure is 9
Removing 1
Size of data structure is 8
Removing 2
Size of data structure is 7
[code]....
As you can see, when I am calling the second for loop, none of the elements are being removed by my methods but the first for loop is working just fine.
Here is my code for the OrderedVector
package data_structures;
import java.util.Iterator;
import java.util.NoSuchElementException;
public class OrderedVector<E> implements OrderedListADT<E>{
private int currentSize, maxSize;
private E[] storage;
public OrderedVector(){
currentSize = 0;
[code]....
So overall, my remove method should implement binary search and remove elements using either an index or the object value type.
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Apr 14, 2015
I am working on my generic insertion sort program. When I completed and run my code, I am having trouble with my code. So, I am just trying to see if I get an correct array from a file. However, i just get so many nulls in the array. Therefore, I can't run my insertionSort function because of null values.
Here is my code
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
[Code].....
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Nov 18, 2014
So I have a persons class:
public class Person
{
private String name;
private int age;
public Person (String name, int age) {
this.name = name;
this.age = age;
[Code] .....
And I need to write a simple main method that creates lots of instances of the Person class and adds them to a generic instantiation of a Collection (ArrayList). And I need to make it so I as a programmer can define how many instances to create.
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Jan 16, 2014
I want to make some library interfaces for a graph.Using these interfaces:
Graph<V,E>
Edge<E>
Vertex<V>
how can i constraint users of this library to use the same type <E> in the graph and edge interface and type <V> in the graph and vertex interface??
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Jul 21, 2014
So I have this class containing all my Enum types, also including methods for fetching Enum types based on their title attribute:
abstract class Enums {
static private Landmass getLandmass(String name) {
for ( Landmass l : Landmass.values( ) ) {
if(l.title.equals(name)){
return l;
[Code] .....
The second method (getAttribute) is created by copy-paste and I also need to repeat this exercise with several other types of Enums. This seems like a waste of code however.
Instead, I thought I'd create a generic method for fetching any type of Enums. As far as I could follow the tutorial @ Oracle I need a generic class for this. Thus the EnumHelper class:
abstract class EnumHelper<T> {
private T getEnum(T type, String name) {
for ( type t : type.values( ) ) {
if(t.title.equals(name)){
return t;
}
}
return null;
}
}
This, however, doesn't compute:
horoscopeEnums.java:234: error: cannot find symbol
for ( type t : type.values( ) ) {
^
symbol: class type
location: class EnumHelper<T>
where T is a type-variable:
[Code] ....
2 errors
To be honest I haven't been able to make much sense of the documentation on generics, thus its no surprise I'm stuck.
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Apr 26, 2013
I want to build a generic exception handler which can be reused in any java j2ee applications. I have java application which is communicating with other 3rd party applications like webservices, webmethods , etc from where we are getting an error code which will be used in our java application to do a lookup to get the respective error message from the resource bundle. Please clarify in such case how I can go with a generic exception handler which will be build separately and will be integrated with Java applications to handle the exceptions and errors.
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May 12, 2014
I am given the task to create a program that evaluates infix expressions using two generic stacks, one operator stack and one value stack.
This is my GenStack.java file:
import java.util.*;
public class GenStack<T>{//T is the type parameter
private Node top;//top of stack
public class Node {//defines each node of stack
T value;
Node next;
[Code] ....
I'm having trouble with the eval and apply methods. The eval method doesn't appear to pickup ')' characters, like it doesn't even see them.
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Jul 15, 2014
I am following this article : [URL] ....
It is important to note that the inference algorithm uses only invocation arguments, target types, and possibly an obvious expected return type to infer types. The inference algorithm does not use results from later in the program.
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Apr 10, 2014
Generic methods are methods that introduce their own type parameters. This is similar to declaring a generic type, but the type parameter's scope is limited to the method where it is declared. Static and non-static generic methods are allowed, as well as generic class constructors.
1. The method is only exclusively to be used for the declared argument parameter? For example given a generic method:public static <String, Integer> boolean method(Pair<K, V> p1) {}I could only invoke the method if Pair argument parameter is <String, Integer>?
2. Or, it will return a <String, Integer> value?
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May 16, 2008
I have set up a project in Eclipse 3.1 and am using java 5.0 compiler.
Here's my folder structure in Eclipse
Java Code:
DFSRemoteClientTestClient.java mh_sh_highlight_all('java');
DFS is the project in Eclipse
And this is how it looks my java class
Java Code:
package RemoteClient;
import java.util.*;
// other imports
public class TestClient {
public static void main(String [] args) throws ServiceInvocationException {
// business logic here ....
}
} mh_sh_highlight_all('java');
So, basically, my java class is just a simple class with a main function.
Now when I build my project, using Project->Clean...
Then I get this as an error at the very first line where i specify the package
This is the error:
Java Code: The type Class is not generic; it cannot be parameterized with arguments <T> mh_sh_highlight_all('java');
What's this error and why am I getting this.
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Aug 28, 2014
Is this the proper way to add to a generic list? My code works just fine, but I got this feeling that there might be some kind of flaw in it or something. Is this pretty much the basic way to add any type of data to a generic list?
import java.util.LinkedList;
public class ListOfGeneric<E> {
private LinkedList<E> myList;
ListOfGeneric(){
myList = new LinkedList<E>();
[Code] ....
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Jul 14, 2014
I am following this article [URL] .... till now I have made some code
This is my Interface
public interface Comparable<T> {
public int compareTo(T o);
}
And this is my class where I am using Bound Type Parameter on Generic Methods
public class GenericMethodBoundType {
public static <T extends Comparable<T>> int countGreaterThan(T[] anArray, T elem) {
int count = 0;
for (T e : anArray)
[Code] .....
What else I need to do both in main method and at what parameterized types I need to pass at the class?
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Jul 11, 2014
I am trying to design a generic RPG game. The issue I am having right now is in my Class I have a subroutine (think that is the correct term) that is basically set up to hold a series of Print Statements. I am really just trying to get some Values that are stored within the Applet, have them assigned to their correct variables and then returned in the print statement. Yet, when I run the applet it just pops up the Applet blank and gives me a long list of errors and I really don't understand when they mean.
Here is the code:
The Class
public class CharacterSheet {
final String NL = System.getProperty("line.separator");
public String characterName;
int playerStr;
int playerCha;
[Code] ....
And the error messages:
Exception in thread "AWT-EventQueue-1" java.lang.NullPointerException: String is null
at sun.java2d.SunGraphics2D.drawString(Unknown Source)
at TFApplet.paint(TFApplet.java:15)
at javax.swing.RepaintManager$3.run(Unknown Source)
at javax.swing.RepaintManager$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
[Code] .....
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May 31, 2014
Ok here are my 2 Classes
Both have Identical Fields
package com.Lists;
public class EmployeeOffice implements EmpInterface {
private double salary;
private String name;
private String postion;
private double hoursWorked;
[Code] .....
So if i wanna sort this Generic class using comaparator what do i do... I cant find an answer to this... I wanna sort them on the basis of salary what to do ...
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Jul 26, 2014
I have the following code:
public class CollisionManager<T> {
private boolean collision = false;
private T mainEntity;
public <T extends Entities> void handleCollision(T mainEntity, T secondEntity){
this.mainEntity = mainEntity; // This is illegal.
}
}
Why "this.mainEntity = mainEntity" is incorrect and also show me the correct way to achieve this?
The error I am getting is "Type mismatch: cannot convert T to T"
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Jul 23, 2014
I'm trying to get the input of two jcomboBoxes for example if jcombobox 1 option 1 and jcombox box 2 option 1 is selected result = x
Here is my code:
comboDest1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
//
// Get the source of the component, which is our combo box.
//
JComboBox comboDest1 = (JComboBox) event.getSource();
[Code] ....
How would i achieve this?
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Oct 19, 2014
So why is it that when I attach a KeyAdapter to a JTextField the code in the KeyAdapter will execute, but when I apply that same KeyAdapter to a JComboBox with its edit feature turned on it won't and, more importantly,
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Feb 1, 2015
displaying COM port in Combo box , see my code below , it does not show any error but it does not show COM port in combo box , instead it shows the class name of Communicator with some garbage data .
Code :
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JComboBox;
import gnu.io.CommPort;
import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;
import java.io.IOException;
[code].....
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Oct 18, 2014
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
[Code]....
I am trying to Make A GUI which has a Jcombo box i also want it to have a jlabel that up dates depending on which option the user selects from the JcomboBox
for exampl if i select lion i want it to say you chose lion on the Jlabel and if i choose ostrich i want it to say ostrich and so on
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