Erasure Feature From Generics - Duplicated Bound Error
Jun 14, 2014
The erasures of all constituent types of a bound must be pairwise different, or a compile-time error occurs.
Well I know what type erasure is, and I think I kind got what this statement means. My understanding from it is that if your type parameter has more than one bound and those bounds occurs to be the same type after erasure that is a compile-time error. Is that it?
The only thing I could found related is something like this:
class A<T extends List<Integer> & List<Integer>>{
}
Which as you might know gives the Duplicated bound error.
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Apr 5, 2014
I'm new to java and I write a simple "Five in a row" game. I have a fixed 13*13 board which contains 169 buttons in an arraylist. Everytime player clicks the button the game set a value of 'x' or 'o' to the arraylist name value. And I have a method named isWon() to check if the it is won or not after player click the button. The game sometime gets and index out of bound exception when checking for whose win.
ArrayList<Character> value = new ArrayList<>();
constructor()
{
for (int i = 0; i < 169; i++) {
value.add(' ');
[code]....
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Jan 18, 2014
I am getting error array index out of bound ... Error detail is :
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
at abhiExample.arraytwodiam.main(arraytwodiam.java:27 )
And program is
Java Code:
package abhiExample;
import java.util.Scanner;
public class arraytwodiam {
public static void main(String [] args)
{
char[][] Atrace={};
int i,j,k,l=0,row ,characters;
[Code] ....
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Mar 10, 2014
I need to design 'notepad' application as my assignment.
Requirement: Only text is allowed, all the characters are having same size and font. It should have feature like new, open, save , save as , exit , UNDO , find , replace and font.
For this i use JTextArea and menu bar .
I am able to develop features like new, open, save , save as , exit. Need to implement now UNDO , find , replace and font but struck at 'UNDO'.
UNDO feature should be enable only when user writing in the writing area but not when it opens any file. What i thought is to have a flag on whenever user save whatever he wrote and if he use select UNDO then it check for the flag. If flag is ON then it will not do UNDO and if flag is not set then it cleared everything from the Text Area.
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Jul 14, 2014
I have three JComboBoxes. When the user selects an entry in the first JComboBox the entries in the second are set. For this I use an Action extends AbstractAction which is bound to the first JComboBox.
I have also bound an Action to the second JComboBox.
Problem: this also fires when the entries on the second JCombox are added which leads to a Nullpointer.
I need a Listener which only reacts to user input, and does not react when the model of the JComboBox is changed.
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Dec 15, 2014
When I am trying to execute this code it is showing
Java Code:
class Sort2D
{
public static void main(String...s) {
Sort2D r=new Sort2D();
int z[][]=r.sort(new int[][]{{1,0,567,4,3,33},{333,677,34243,8987,3434,324},{446,876,23,546565,332}});
for(int i=0;i<z.length;i++)
for(int j=0;j<z[i].length;j++)
System.out.println(z[i][j]);
[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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Apr 21, 2015
I'm using json to submit form from web and mobile, I want to add uploading image feature to this form. How can I do that with code if possible?
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Feb 24, 2014
As of now am using icefaces 1.8.2 provided tags for downloading data into excel sheet where i can download all the data from a data table. But now the requirement is like need to download the data into excel sheet based on values passed from UI as parameters to the action class method.
Attaching the code snippet along with this post.
CustomerList.xhtml :-
<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tr>
<td>
<ice:outputLabel value="Export:" />
[Code] ....
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Nov 8, 2014
Basically I am trying to make a POS system and need a way to print a receipt whether there are 1 items sold or 50. So I used a Arraylist. This is the format for the printer that is needed:
printer.printNormal(POSPrinterConst.PTR_S_RECEIPT, " 2 200 Tx Hashi Chop Sticks" + LF);
This is what I tried to do:
ArrayList<String> receiptLine = new ArrayList<>();
public void captureSales(){
receiptLine.add("Test");
System.out.println("Size of the receipt list is: "+receiptLine.size());
System.out.println("Element at index 1: " + receiptLine.get(0));
printer.printNormal(POSPrinterConst.PTR_S_RECEIPT, " " + receiptLine.get(0) + LF);
Error:
Size of the receipt list is: 1
Element at index 1: Test
java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
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Mar 12, 2015
I am tring to run LDA to generate some topics from txt files as the following one:
Document1 label1 forest=3.4 tree=5 wood=2.85 hammer=1 colour=1 leaf=1.5
Document2 label2 forest=10 tree=5 wood=2.75 hammer=1 colour=4 leaf=1
Document3 label3 forest=19 tree=0.90 wood=2 hammer=2 colour=9 leaf=4.3
Document4 label4 forest=4 tree=5 wood=10 hammer=1 colour=6 leaf=3
Each numeric value in the file is an indication of the number of occurrences of each feature (e.g., forest, tree) multiplied by a given penalty. To generate instances from such a file, I use the following Java code:
String lineRegex = "^(S*)[s,]*(S*)[s,]*(.*)$";
String dataRegex = "[p{L}([0-9]*.[0-9]+|[0-9]+)_=]+";
InstanceList generateInstances(String dataPath) throws UnsupportedEncodingException, FileNotFoundException {
ArrayList<Pipe> pipeList = new ArrayList<Pipe>();
pipeList.add(new Target2Label());
[Code] .....
I then add the so-generated instances to my model using the instruction model.addInstances(generatedInstances). The resulting output is described below.
It contains errors caused by the instruction model.addInstances(generatedInstances). Debugging my code showed me that the alphabet associated to the model is null. Am I using the wrong iterator?
name: document1
target: label1
input: TokenSequence [forest=3.4 feature(forest)=3.4 span[0..10], tree=5 feature(tree)=5.0 span[11..17], wood=2.85 feature(wood)=2.85 span[18..27], hammer=1 feature(hammer)=1.0 span[28..36], colour=1 feature(colour)=1.0 span[37..45], leaf=1.5 feature(leaf)=1.5 span[46..54]]
Token#0:forest=3.4 feature(forest)=3.4 span[0..10]
[Code] ....
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Apr 22, 2014
I need to be able to detect IE 9, IE 10, IE 11 and the latest from Firefox and Chrome. The old method using the user-agent string is unreliable and not recommended. There is a different approach called, "Feature Detection". But I need to know what features to test to determine the browser. I can write it myself, or if there is a handy dandy API using feature detection already written that would be OK too.
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Nov 25, 2014
So lets say I got maximum of 20 deposit, I want to create a method/function (idk what proper name for it is) so that you cannot deposit more than 20 nor withdraw more than you have in your account, so this function checks your account, if your total is for example 18 and you're trying to deposit 10, it rejects it and doesn't add to your total and pops up with a message, vice versa for withdraw.
This is what I have so far
Not I already have the maximum limit + total feature created just not displayed here
public void depositMoney (int dMoney) {
if(DMoney > 0 ) {
totalMoney = totalMoney + dMoney;
}
else {
System.out.println("Please insert money more than 0");
[Code] .....
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Nov 25, 2014
So lets say I got maximum of 20 deposit, I want to create a method/function (idk what proper name for it is) so that you cannot deposit more than 20 nor withdraw more than you have in your account, so this function checks your account, if your total is for example 18 and you're trying to deposit 10, it rejects it and doesn't add to your total and pops up with a message, vice versa for withdraw.
This is what I have so far . Not I already have the maximum limit + total feature created just not displayed here
Java Code:
public void depositMoney (int dMoney) {
if(DMoney > 0 ) {
totalMoney = totalMoney + dMoney;
} else {
System.out.println("Please insert money more than 0");
[Code] ....
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Mar 20, 2015
What is wrong in this
class Gen<k,v>
{
K a;
V b;
Gen(K s, V f) {
a=s;
b=f;
[Code] .....
a is object of type k,then how can I retrieve content of a?
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Jan 29, 2014
I have studied that Generics are used to shift the Class Cast Exception into Compile time errors , So that we get errors at compile time error and we do correct them before executing ,but Here is a program in which i am getting Class Cast Exception
class Animal
{
}
class Dog extends Animal
{
}
class Cat extends Animal
[code]..
Getting Exception at line no 29 which i know why it occurs but just wanna ask that isn't it should be caught at compile time According to Generics ?
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Jun 19, 2014
I just want to clarify generics for classes.
Referring to [URL] ....
Generics means all methods in class Box will return an Integer if their parameters are defined as T when the instantiation is :
Box<Integer> integerBox = new Box<Integer>();
Are those Boxes only can contain Integers? Can I write
Box <Toys> toybox = new Box <> ();
To show that the Box only contain toys?
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Jun 17, 2014
Set<? super TreeMap> s = new HashSet<SortedMap>();
SortedMap<String,String> sm = new TreeMap<String,String>();
TreeMap<String,String> tm = new TreeMap<String,String>();
s.add(sm); //This fails
s.add(tm);
Why does adding sorted map to a Set that allows ? super TreeMap and instantiated as such fail?
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Apr 10, 2014
public int[] allIndicesOf(E itemSought) {
ArrayList<Integer> toUse = new ArrayList<>();
for (E anArray : container) {
if (anArray.equals(itemSought)) {
toUse.add(container.indexOf(itemSought));
[Code] ....
I have an array list of strings. I want to be able to return an array of integers telling me which indexes in the string array list contain the itemSought object.
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Feb 14, 2014
Suppose I have
class A {
public void speak() {
System.out.println("I am class A");
}
}
class B extends A{
public void speak() {
System.out.println("I am class B");
}
}
class C extends B{
public void speak() {
System.out.println("I am class C");
}
}
Why this doesn't work while A is a super type of B ?
public static void insertElements(List<? super B> list){
list.add(new A()); //not OK, why?
}
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Feb 22, 2015
Why java uses the keyword extends when setting the bound of a type parameter(Generic) to an interface. I think using the keyword implements is more intuitive.
public static <T extends Comparable<T>>
why use extends? and not implements.
int countGreaterThan(T[] anArray, T elem) {
int count = 0;
for (T e : anArray)
if (e.compareTo(elem) > 0)
++count;
return count;
}
I know if I want to set multiple bounds I will use extends keyword, and I will concatenate the bounds using & operator.
Is this a design decision to always use extends keyword to set bounds?
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Jul 27, 2014
An array of references to a specific generic type is not allowed in Java.
e.g.,
ArrSpec<String> arrs[] = new ArrSpec<String>[10];
is not allowed though the type checkng and memory allocation can be done at the compile time itself.
Instead of this, Java allows to use Wildcard type array of references to a generic type.
e.g.,
ArrSpec<?> arrs[] = new ArrSpec<?>[10];
is allowed though the type checking, memory allocation and any type of values to be stored would be decided at the runtime.
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Jun 5, 2015
My book defines this generic method
Java Code:
public static <E extends Comparable<E>> void sort(E[] list... mh_sh_highlight_all('java');
Comparable is an interface and from how i look at this piece of code is that I can only use a class that implements the Comparable interface; however, this is the context my book uses when explaining the following code
First, it specifies that E is a subtype of Comparable.
Second, it specifies that the elements to be compared are of the E type as well.
What does it mean when it says E is a subtype.
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Mar 6, 2014
I've an interface with generic methods in it. I would like to have specialized methods in the sub types. While doing that I'm seeing the following warnings in eclipse.
class Sorter {
<E> void sort(E[] elements);
};
class StringSorter {
// This gives me a warning 'hiding' to 'sort'
<String> void sort(String[] elements) {
}
// Gives me an error "The method someCrap(String[]) in the type StringSorter is not applicable for the arguments (String[])"
void someCrap(String[] elements) {
}
};
I would like to understand why eclipse gives the above warnings and errors.
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Dec 15, 2014
is the Java upcating and downcasting rules are same for general object type or generics types?
1) Dog dog = new Animal();
Type mismatch can't covert Dog to Animal - complie time error
2) Animal animal = new Animal();
Dog dog = (Dog) animal;
java.lang.ClassCastException: Animal cannot be cast to Dog at runtime.
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Oct 25, 2014
I'm working with Doubly Linked Lists and using Java Generics..
My nodes looks like this:
class DNode<E> {
DNode<E> previous;
DNode<E> next;
E element;
//and all methods inside
}
My list of Nodes looks like this:
class DLL<E>{
private DNode<E> head;
private DNode<E> tail;
private int size;
[code]....
As you can see, as arguments they get "E o"...I need to write a program, which from the main function asks the users how long is the list, and after they type it's length, I ask them to start typing the elements (integers)...and this is how my main method is written, but I can't seem to make it work, specialy when I call the "insLast" method,I guess it's because the arguments i'm giving to the function...how to read the elements and write them into the list?
public static void main(String[] args) throws IOException {
DLL<Integer> lista=new DLL<Integer>();
BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
String s = stdin.readLine();
int N = Integer.parseInt(s);
s = stdin.readLine();
String[] pomniza = s.split(" ");
for (int i = 0; i < N; i++) {
lista.instLast(Integer.parseInt(pomniza[i]));
}
}
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