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] ....
Got a problem with generics, which I'm still pretty new at. Here's a program that compiles fine:
import java.util.ArrayList;
import javax.swing.JComponent;
public class Experiments {
public static void main(String[] args) {
ListHolder holder = new ListHolder();
[Code] ....
It's useless, but it compiles. If I change Line 14, however, to add a generic type parameter to the ListHolder class, Line 10 no longer compiles:
import java.util.ArrayList;
import javax.swing.JComponent;
public class Experiments {
public static void main(String[] args) {
ListHolder holder = new ListHolder();
[Code] ....
I get this error:
Uncompilable source code - incompatible types: java.lang.Object cannot be converted to javax.swing.JComponent
at experiments.Experiments.main(Experiments.java:10)
Apparently, the introduction of the type parameter leaves the compiler thinking that aList is of type Object. I can cast it, like this:
JComponent c = ((ArrayList<JComponent>)holder.aList).iterator().next();
That makes the compiler happy, but why is it necessary? How does adding the (unused) type parameter to the ListHolder class end up making the compiler think the aList member of an instance of ListHolder is of type Object?
I have a String repersentaion of some Object.I want that object convert back into some class type how can I do this?
View Replies View RelatedI 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??
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.
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?
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.
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?
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"
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] .....
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.
I have the following code in which I am looping through the rows of one array (composed of Strings) and copying it to another array. I am using .clone() to achieve this and it seems work as it changes the memory location of the rows themselves. I did notice that the String objects are still pointing to the same location in memory in both arrays but I won't worry about that for now, at the moment I just want to understand why the array I am cloning is not successfully assigning to the other array.
This is the incorrect line: ar[r] = maze[r].clone();
My code:
private String[][] maze = {{"*","*","*"," ","*","*","*","*","*","*"},
{"*"," ", "*"," "," "," ","*"," ","*","*"},
{"*"," ","*","*","*"," ","*"," ","*","*"},
{"*"," "," "," "," "," "," "," "," ","*"},
{"*","*","*","*","*"," ","*","*","*","*"},
{"*","*","*","*","*"," ","*","*","*","*"}};
//private String[][] mazeCopy = copyMaze(new String[6][10]);
private <T> T[][] copyMaze(T[][] ar){
for (int r = 0; r < ar.length; r++){
ar[r] = maze[r].clone();
}
return ar;
}
My compiler says: Required: T[]. Found: java.lang.String[]
Since ar[r] is an array and .clone() also returns an array why is this line incorrect.
method passing null to the called function, compiler would take that parmer as what type of paramer???
View Replies View RelatedI have some class called sorted to sort the linked list through the nodes of the list. and other class to test this ability, i made object of the sort class called "list1" and insert the values to the linked list.
If i make other object called "list2" and want to merge those two lists by using method merge in sort class. And wrote code of
list1.merge(list2);
How can the merge method in sort class know the values of list1 that called it as this object is created in other class.
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.
Here is a small part of my program
Java Code:
// for every attribute not mentioned in the rule r
enumAtt = ruleE.enumerateAttributes();
while (enumAtt.hasMoreElements()) {
Attribute attr = (Attribute) enumAtt.nextElement();
if (isMentionedIn(attr, r.m_test)) {continue;}
int M = attr.numValues();
[Code] ....
It repeats only the last rule , why is that !!!!!!
Here I have an enum class
public enum Money{
ONE_PENNY(1),
TWO_PENCE(2),
FIVE_PENCE(5),
TEN_PENCE(10),
TWENTY_PENCE(20),
FIFTY_PENCE(50),
ONE_POUND(100),
TWO_POUNDS(200);
private int coin;
Money(int c) {
coin = c;
}
int showCoin() {
return coin;
}
and for a test class, I need an array list with a couple of coins in it (i.e. ONE_POUND, TWO_POUNDS) and a loop that adds together the values of the coins in the list and prints the result. How can I do this?
Im making a simple code to add an array to a List (the code im referring to is <String> )
import java.util.*;
public class L5_ArrayListProgram {
public static void main(String[] args){
String[] things = {"lasers","ghouls", "food", "dark"};
List<String>list1 = new ArrayList<String>();
for(String x: things)
list1.add(x);
My simple question is - what are the <String> ...<String> for? I understand it makes the list1 variable a string, but why is it made like this? do we usualy use <String> when we need to make a variable a String?
I am trying to add images to go with my wordlist but unsure of how to do this.
public class WordRepository {
I was supposed to write a PolyNode class for each node in the LinkedList, and a Polynomial class which is pretty much the list itself.Here is what I've coded so far:
PolyNode class:
public class PolyNode {
private int coefficient;
private int exponent;
private PolyNode next;
[code]....
The only trouble I'm having with this problem is finding a way to add these two polynomials together. My first attempt at it was to use nested while loops to traverse through both polynomial lists, like so:
public Polynomial addPolynomials(Polynomial p1, Polynomial p2) {
PolyNode current1 = p1.getFirstNode();
PolyNode current2 = p2.getFirstNode();
int coeff;
int expo;
Polynomial polySum = new Polynomial();
[code]....
Basically what this method does:
-Check to see if the exponents between two terms are the same
-If true, add their coefficients together
-Create a new node for the polySum with that coefficient sum and the particular exponent value
-At the end, return the polySum list which should be the sum of two polynomials
The problem with this method is it doesnt account for the values that are left behind because their exponents aren't equal to the exponents of the other list. So, the only terms that are getting added into the sum list are the ones that have the same exponent in both of the lists that are being added together.
I'm having trouble completing my homework. The problem:
>Suppose that you want an operation for the ADT list that adds an array of items to the end of the list. The header of the method could be as follows:
public void addAll(T[] items)
>Write an implementation of this method for the class LinearLinkedList
At first this seemed like an easy problem to me. This is the solution I came up with:
public void addAll(T[] items) {
int length = items.length;
for(int i = 0 ; i < length; i++){
this.addLast(items[index]);
}
}
However, one of the requirements for the assignment is that we're not allowed to use the addLast method. how else to insert items to the Linked List without this method. These are the user-defined LinearLinkedList and ListNode classes we made during class:
**LinearLinkedList**
// Linear linked list class
import java.util.NoSuchElementException;
public class LinearLinkedList {
[code]....
I am working on an assignment that requires me to implement 2 methods (add() and remove()) and create an inner class (OrderedListNode). I must use data items of type Comparable. The items should be sorted.
I understand what needs to be done, but I am having a difficult time actually writing the code. I added the main method to check to see if my code works, and it doesn't seem like that is even being read.It compiles without error - it only gives a warning of unchecked or unsafe operations.
Code:
package dataStructures;
//This class functions as a linked list, but ensures items are stored in ascending order.
public class OrderedLinkedList {
//return value for unsuccessful searches
private static final OrderedListNode NOT_FOUND = null;
[code]...
I want to create a program where I need to create an object of list type such as text file will contain nos like 1,2,3,4,5 and write into text file and delete the in FIFO order i.e 1,2,3,4,5...how i can achieve to write a program? I tried bt everytime got concurrent modification exception or Array out of bound exception.
View Replies View RelatedThis is supposed to be a method that adds stars after each item in the list.
Java Code:
import java.util.ArrayList;
public class ClientProgram {
public static void main(String[] args) {
ArrayList<String> list = new ArrayList<String>();
list.add("the");
[Code] ...
I'm guessing it's because list.size() changes, though but it should only find that value in the beginning, so it shouldn't be a problem?
If I specify the directory in file type or path string type how can I get a list of files that are file type .yml in that folder, so I can loop through and do something with each single file.yml in that specified directory.
View Replies View RelatedHave a user who cannot access a file on website for work he needs to do. He gets these errors:
His Java is the latest and I have already added the site to the exceptions list in, Java and the browser, but I can't get through.