Generic Method And Bound Type Parameter Errors

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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Addition Of Generic Type Parameter Causes Member Type Clash

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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Parametrized Array Type As Method Parameter?

Jul 31, 2014

I have the following method:

public static void doSomething(List<? extends GenericClass> input)
{
// op
}

^

This compiles and works, ensuring I can only pass in a List of a type extending GenericClass.But now I want it to accept an Array instead of List. This is where I'm stuck:

public static void doSomething(<? extends GenericClass>[] input)
{
// op
}

^

A wrong guess at the syntax which does not compile. One solution is to convert Array into ArrayList before calling the 1st method above, but I'd rather bypass this if possible.

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How To Get Access To The Method With A Parameter Of Class Type Variable

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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How To Convert String Type To Generic Class Type

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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Generic Method In Generic Class

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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Interfaces Using Generic Type Constructions

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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Type Inference With Constructor Of Generic Class

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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Generic Methods Introduce Their Own Type Parameters

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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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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Adding Any Type Of Data To A Generic List?

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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Cannot Assign Generic Object Reference To Similar Type

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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First Time Using Generics - Incomparable Type Errors

Aug 29, 2014

I am trying to make a generic method that will replace the data type T with those number types usable with a Scanner object. However, whenever I try to compile, I get errors saying that a Byte/Integer/Double etc are found when only a type T is allowed. This is the beginning of my method. I can;t understand what is wrong with it.

Java Code:

public <T extends Number> T nextRanged(T lowerBound, T upperBound, boolean inclusive, String errorMessage){
// Holds program execution until user inputs a numeric value between the bounds. Prevents all other input without exception.
// Output data type determined by the type of the bounds.
T input = null;
try{
if(input instanceof Byte){
input = new Byte(internalScanner.nextByte());

[Code] ....

The purpose of the method, in the end, will be to provide the nextXXX() functionality of a Scanner object but with built in validation procedures. I could easily do this by making a nextIntRanged(), nextDoubleRanged() etc methods, but this seems wasteful to me.

I meant "incompatible type errors"!

Error example:

ValidatedScanner.java:57: error: incompatible types
input = new Byte(internalScanner.nextByte());
^
required: T
found: Byte

where T is a type-variable:

T extends Number declared in method <T>nextRanged(T,T,boolean,String)

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Printing Errors If F Or C Isn't Entered For Temperature Type

Nov 14, 2014

I am trying to get it to print out an error if F or C isn't entered for the temperature type, but the code I am taking from one of my other similar programs isn't working for some reason.

Also, when I type a string in the temperature I get an exception....I can do the same with that as I would the temp type? I think I may just be putting the code in the wrong spot and thats why it isn't working..

public static void main(String[] args)

Scanner input = new Scanner(System.in);
System.out.print("Please enter F for Fahrenheit or C for Celsius: ");
String fOrC = input.next();

[Code] ....

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Identifier Expected And Illegal Start Of Type Errors

Aug 6, 2014

I'm working through Head First Java, and I'm struggling with the chapter 6 magnet exercise on page 161. I've checked my answer countless times, and it appears to match the book's code, but when I try to run it on my computer I'm getting an error. It says:

error: <identifier> expected
System.out.println^(" "); and

error: illegal start of type
System.out.println(^" ");, both for line 32.

I cannot seem to figure out what is different about my code!!

import java.util.*;

public class ArrayListMagnet {
public static void main (String [] args) {
ArrayList<String> a = new ArrayList<String>();
a.add (0, "zero");
a.add(1, "one");
a.add(2, "two");
a.add(3, "three");

[Code] .....

Also, I'm not sure if this has anything to do with the above errors, but I'm getting a third error message for line 34 saying:

error: class, interface, or enum expected
}^.

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JDBC :: How To Determine DATE Data Type Of Parameter If It Is Not Specified

Feb 2, 2015

Oracle JDBC driver determine the DATE data type of parameter correctly without any typecasting.

Example:
ps = conn.prepareStatement("SELECT ? FROM DUAL");
ps.setObject(1, Date.valueOf("2014-01-11")) ;
 
I have tried the same example with other database driver but it gives error.

PostgreSQL JDBC driver:
org.postgresql.util.PSQLException: ERROR: could not determine data type of parameter $1
 
ps = conn.prepareStatement("SELECT ?");
ps.setObject(4, Date.valueOf("2005-01-01"));
 
so I want to know how Oracle JDBC driver determine the DATE data type of parameter.

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JDBC :: Determine DATE Data Type Parameter If It Is Not Specified?

Feb 2, 2015

Oracle JDBC driver determine the DATE data type of parameter correctly without any typecasting.

Example:
ps = conn.prepareStatement("SELECT ? FROM DUAL");
ps.setObject(1, Date.valueOf("2014-01-11"));
 
How Oracle JDBC driver determine the DATE data type of parameter.

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Cannot Assign Cloned String Array To Generic Type Array

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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Using Method Calls With Returns But It Keeps On Showing Errors

Oct 12, 2014

I am trying to use method calls with returns but it keeps on showing errors. The errors say class, interface, or enum expected. I realize this error occurs if there is issue with declaring class - but i can't seem to find the error. I will post the code that shows error.
 
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.text.*;
public class FuelCost extends JFrame
{
// declarations
Color black = new Color(0, 0, 0);

[Code] ....

The error states:

C:UsersPriti BhattaraiDesktopCCAC JavaFuelCost.java:290: error: ';' expected
public double calculateCostToFillTank()
^
C:UsersPriti BhattaraiDesktopCCAC JavaFuelCost.java:292: error: class, interface, or enum expected
return (averageMilesPerTank / milesPerGallonRating) * currentPricePerGallon;

[Code] ....

12 errors

Tool completed with exit code 1

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Method Overridden In Method Parameter?

Jul 20, 2014

I was following a tutorial for libGdx and suddenly became confused by the following syntax:

up.addListener(new ClickListener(){
public void clicked(InputEvent event, float x, float y){
position.y += 1f;
//currentFrame = animation.getKeyFrame(12);
}
});

"up" is basically a text Button:

TextButton up = new TextButton("up", textButtonStyle);

and .addListener is just one of the methods "TextButton" has (actually I think its inherited from "Button" but that doesn't matter).

Basically my question is what's going on inside the parentheses? From what I see its a new instance of "ClickListener" but then suddenly they override an actual method within. Is this simply just a way to override a method from the ClickListener class or is it something else?

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Java Game Errors - No Suitable Method Found For Intersect JButton

Apr 9, 2014

I am receiving two errors that I'm not sure how to fix. The first is illegal start of expression at line

"public void actionPerformed(ActionEvent e)"

and no suitable method found for intersect JButton at line

"if(blocker01.getBounds().intersects(r_wall))" .
 
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
 public class gamePanel01 extends JPanel implements KeyListener {
character ch1 = new character("Hero");

[Code] ....

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Initializing Constructor As Parameter For A Method?

Jan 2, 2014

So, I am learning Swing, and Swing Layouts. I just came across a really confusing (for me) line of code.

Java Code:

setLayout(new BorderLayout()); mh_sh_highlight_all('java');

So, this is weird for me because I don't really understand why the BorderLayout class constructor is being initialized as a parameter for the setLayout..

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Passing A Boolean Parameter From One Method To Other

Jan 30, 2015

Java SE Runtime Environment build 1.8.0..This is part of the code:

public static int addAddress (String[] number, boolean[] front, double[] total) {
int num = 0;
double ffee = 0;
/*boolean value = false;*/
 
[code]...

I have tried using the line of code commented out, /*boolean value = false;*/. However, another error is displayed. The compiler shows the following...

Inspection.java:33: error: incompatible types: boolean cannot be converted to boolean[]
front[num]= defineFront(num, value);
^
Note: Some messages have been simplified; recompile with -Xdiags:verbose to get full output error...I know that boolean values are by default stored as false, once you create the array. However, I'm having trouble passing the variable to the method.

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Method That Accept Object As A Parameter

Jan 3, 2015

I have a method that accepts as a parameter an object:

public void addClient(Client c){ }

Client is a class which has a constructor that has two String parameters:

public Cliente (String name, String lastname){
this.name = name;
this.lastname = lastname;
}

In the main add a Client in this way:

addClient(new Cliente("first", "second"));

Now, i have an array of Client, so I would like to enter within this. Example:

public void addClient(Client c){
for (int i = 0; i<client.length ; i++) { // client is an array of Client object
client[i] = c; // Enter a c in the array, but does not work!
System.out.println("test "+clienti[i]); // print Client@15db9743
}
}

I have used the println for check if worked insertion, but the result shows no

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How Is Class Cast In Method Parameter

Jan 15, 2014

how is cast a class at a methods parameters? i have a problems in a methods paramter. i draw red line my exception and mymethods is orage color ....

Caffe drink = new Caffe();
CoffeCup cup = new CoffeCup();
cup.setTempeture(100);
drink.drinkcaffe((CaffeCup)(cup.getTempeture()));

[code]....

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Using Comparable Or Comparator As Parameter In Method

Jul 1, 2013

I was going through some lectures online and found that to compare or even swap, the use of comparable or comparator argument like
 
public static boolean less(Comparable v,Comparable w)
{
     return v.compareTo(w)<0;
}
 public static void swap(Comparable []a,int i,int j)
{
     Comparable swap=a[i];
     a[i]=a[j];
     a[j]=swap;
}
 
I did not get the use of passing Comparable or Comparator to the function as parameters. Object as parameter could have been used too?

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