Type Class Is Not Generic - It Cannot Be Parameterized With Arguments
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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Mar 22, 2015
I have a String repersentaion of some Object.I want that object convert back into some class type how can I do this?
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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 22, 2014
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?
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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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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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May 1, 2014
At the beginning of one of my classes, I instantiate some List objects. For example ...
Java Code: private List<> byName = null; mh_sh_highlight_all('java');
... then later, I reference this again in a method like this:
Java Code: byName = new ArrayList<>(rs.getString("firstName"), rs.getString("Last Name")); mh_sh_highlight_all('java');
This is where I get the error. I've tried making the list of <String>, but that didn't make a difference.
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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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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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Jun 5, 2014
I am totally new to Java. What is the purpose of this method?
Flow of the int x=3; like where does the 3 go step by step?
Passing Primitive Data Type Arguments (from oracle java tutorials)
Primitive arguments, such as an int or a double, are passed into methods by value. This means that any changes to the values of the parameters exist only within the scope of the method. When the method returns, the parameters are gone and any changes to them are lost. Here is an example:
public class PassPrimitiveByValue {
public static void main(String[] args) {
int x = 3;
// invoke passMethod() with
// x as argument
passMethod(x);
[Code] ....
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Oct 21, 2012
Primitive arguments, such as an int or a double, are passed into methods by value. This means that any changes to the values of the parameters exist only within the scope of the method. When the method returns, the parameters are gone and any changes to them are lost.
Reference data type parameters, such as objects, are also passed into methods by value. This means that when the method returns, the passed-in reference still references the same object as before. However, the values of the object's fields can be changed in the method, if they have the proper access level.For example, consider a method in an arbitrary class that moves Circle objects:
public void moveCircle(Circle circle, int deltaX, int deltaY) {
// code to move origin of
// circle to x+deltaX, y+deltaY
circle.setX(circle.getX() + deltaX);
circle.setY(circle.getY() + deltaY);
// code to assign a new
// reference to circle
circle = new Circle(0, 0);
}
Let the method be invoked with these arguments: moveCircle(myCircle, 23, 56)
Inside the method, circle initially refers to myCircle. The method changes the x and y coordinates of the object that circle references (i.e., myCircle) by 23 and 56, respectively. These changes will persist when the method returns. Then circle is assigned a reference to a new Circle object with x = y = 0. This reassignment has no permanence, however, because the reference was passed in by value and cannot change. Within the method, the object pointed to by circle has changed, but, when the method returns, myCircle still references the same Circle object as before the method was called.
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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 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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Jun 21, 2014
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.
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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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Jun 9, 2014
A method is declared to take three arguments. A program calls this method and passes only two arguments.Will it take the third argument as
1 null
2 void
3 zero
4 Compilation error
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Aug 14, 2014
class Passenger{
String name;
int age;
char gender;
int weight;
public Passenger(){
[Code] ....
This is showing error.....error it gives isthat it cannot change from string type to passenger type......... How to do it??????
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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 15, 2014
There is a sentence in JLS 7 which I can't figure it out. It says :
A cast from a type S to a parameterized type T is unchecked unless at least one of the following conditions holds:
-S <: T
-All of the type arguments (ยง4.5.1) of T are unbounded wildcards
-T <: S and S has no subtype X other than T where the type arguments of X are not contained in the type arguments of T.
Condition one and two I got it. But the number three is really bugging me. I write some code in order to try to understand it.
class G<X>{}
class D<T,U> extends G<T>{}
G<String> g = new G<>();
D<String, Integer> dd = (D<String, Integer>) g;
In Eclipse I got no warning but it shouldn't give one ?
Because g has others subtypes than D<String, Integer> (e.g. D<String, List> , D<String, G>)
Am I missing something about the contained type arguments ?
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May 2, 2014
If i used parameterized constructor in servlet what happens in deployment time?
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Dec 4, 2014
I'm developing a JSF application.I have some enums, for example
public enum Gender {
MALE("Male"),
FEMALE("Female");
private final String label
[code]....
I want to put the enum value in <h:selectOneMenu>. I use a bean:
@Named(value = "genderBean")
@RequestScoped
public class GenderBean {
/**
* Creates a new instance of GenderBean
*/
public GenderBean() {
[code]...
How can i call the method .values() of enum for a generic enum T, like in the striked code?
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Mar 27, 2014
I am trying to use a custom class in a .jsp page, as part of a course I am taking on Web Technologies.The original version of the jsp page was working fine, until I moved part of the Java code to a separate class.Here is the original .jsp code that is working:
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" lang="en-GB" xml:lang="en-GB">
<%@page pageEncoding="utf-8" %>
<head>
<meta charset="UTF-8" />
<title>Forum</title>
<link rel="stylesheet" type="text/css" href="stocktails.css" />
</head>
<body>
[code]....
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Feb 10, 2015
I'm really new to object/class concepts and already having difficulties with applying them. How to create and return an array of Exam objects? I need to get a data from a textfile which is passed to the method.
Java Code:
public Exam(String firstName, String lastName, int ID, String examType, int score) {
this.firstName = firstName;
this.lastName = lastName;
this.ID = ID;
this.examType = examType;
this.score = score;
[Code] ....
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Feb 10, 2015
I'm really new to object/class concepts and already having difficulties with applying them. how to create and return an array of Exam objects? I need to get a data from a textfile which is passed to the method.
public Exam(String firstName, String lastName, int ID, String examType, int score)
{
this.firstName = firstName;
this.lastName = lastName;
this.ID = ID;
this.examType = examType;
this.score = score;
[code]....
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Oct 10, 2014
I've got an abstract class
public abstract class AbstractClass
{
//stuff
}
And a few classes that inherit from it
public class Class1 extends AbstractClass
{
//stuff
}
public class Class2 extends AbstractClass
{
//stuff
}
within another class I have a private variable with the type of the Abstract class, and within one of the methods I assign an object to the the variable like this:
public class Test
{
private AbstractClass temp;
public testMethod(){
Class1 anObject = new Class1();
temp = anObject;
}
}
Is this legal? Will temp become a Class1 object?
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Feb 19, 2014
how to get an access to the method with a parameter of class type variable, lets say: public void insert(Record newRecord, int pos)?
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