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Java Collection Q&A » Generic » compiler 

1. Xcode: 'Generics are not supported in -source 1.3' compiler error?

just a quick question: I am a CS undergrad and have only had experience with the Eclipse, and Net Beans IDEs. I have recently acquired a Macbook and was wanting to ...

2. Java - local class and generics, why compiler warning?

Named local classes are very rarely used, usually local classes are anonymous. Does anybody know why the code below generates a compiler warning?

public class Stuff<E> {
  Iterator<E> foo() ...

3. Java generics compiler error

When doing some not really fancy things with Java, I came over an error with generics that I was not able to understand why it doesn't work. The code is:

package test;
import ...

4. Is it possible to solve the "A generic array of T is created for a varargs parameter" compiler warning?

This is a simplified version of the code in question, one generic class uses another class with generic type parameters and needs to pass one of the generic types to a ...

5. java compiler oddity: field declared in same class, yet "not visible"

The eclipse compiler refuses to compile the following code, stating that the field s is not visible. (IBM's Aspect J compiler also refuses, stating that "s could not be resolved") Why ...

6. How do I get the Java compiler to tell me what type it infers?

When I have a Java generic function like:

<T> T choose(T a, T b) { }
and I call it from somewhere, how can I find out what type is inferred for T? Edit: ...

7. Is there a non-type-erased generics extension to the Java Compiler available as a 3rd party compiler extension?

I'm becoming increasingly frustrated with the limits of type-erased Java generics. I was wondering if there was a custom Java Compiler that provided a full version of generics without the quirks ...

8. Weird generics issue

Does anyone know why the following code does not compile and during compilation I get incompatible types exception ?

public class Test<T> {

public static void main(String[] args)
    // using ...

9. Avoiding compiler warning when implementing interface with bounded return type

How can I implement the ContactService interface without getting warning about unchecked conversions from the compiler:

interface ContactsService
    <T extends Response> T execute(Action<T> action);

interface Action<T extends Response> { }

interface ...

10. Multiple wildcards on a generic methods makes Java compiler (and me!) very confused

Let's first consider a simple scenario (see complete source on

import java.util.*;

public class TwoListsOfUnknowns {
    static void doNothing(List<?> list1, List<?> list2) { }


11. Compiler warning when casting to generic method type variable in Java

Edit: I initially accepted thejh's answer, but I wasn't really satisfied with it since I wanted to make proper use of generics. So, I kept doing research and found a solution. ...

12. Generic Method Covariance - valid restriction or compiler oversight?

Does anyone know the definitive answer to why the following isn't allowed by the java compiler?

class BaseClass {

      public <T extends Number> T getNumber(){

13. What does the Java Compiler do with multiple generic bounds?

Have a look at this (arguably stupid) code:

public <T extends Appendable & Closeable> void doStuff(T object)
throws IOException{

    object.append("hey there");

I know that the compiler removes ...

14. My generics test in Java doesn't work!

I am doing some Java studying, especially in the area of generics. I'm fairly familiar with generics in C#, but in Java, it's a whole different story. I used a few samples that ...

15. Prevent method call using compiler tricks

I have roughly these types:

interface Record {}
interface UpdatableRecord extends Record {}

interface Insert<R extends Record> {

    // Calling this method only makes sense if <R extends UpdatableRecord>

16. The inherited method Object.clone() cannot hide the public abstract method

So, I have this bit of wild, crazy code, that is making the compiler spit in my face for some hours the following error:

The inherited method Object.clone() cannot hide the public ...

17. Why does the generic bound "E implements I" result in a compiler error?

Why does this compile:

class MaxMin<E extends Comparable<E>>
   E max=null;
   E min=null;
...but this doesn't?
class MaxMin<E implements Comparable<E>>
   E max=null;
   E min=null;

18. Solution to compiler warning for generic varargs

A puzzle from this blog. Similar to SO1445233. Given the following source listing, explain why the compiler is producing a warning at invocation to the list method and give ...

19. Generics compiler error

I'm using generics in a simple class. I'm getting a compile time error and for the life of me, I can't figure it out. Any held would be appreciated. My class is: public class DB { private static final Map, ? extends Map> db = new HashMap, Map>(); /** * @param ...

20. generics compiler warning

Hi, private static List storeInList(Object object) { List returnList = new ArrayList(); if (object instanceof List) { returnList.addAll(( List )object); // WARNING } else { returnList.add(object); } return returnList; } The line marked WARNING generates the following compiler warning: "Type safety: The cast from Object to List is actually checking against the erased type List" I've tried changing ( List ) ...

21. This Generics work (At least in my compiler)

Ahoy there ! brotherhood of Java (otherwise known as Java Ranch) The following question is about Generics....... I have noticed that it doesn't really matter if you don't write the Generic type of a Collection on the right side, I mean on the actual object as long as you type it on the reference variable side. Like this: List mice = ...

22. Utility like generic compiler

23. compiler promotion rules in generics

Hi, following is the code public T findLarger(T x, T y) { if(x.compareTo(y) > 0) { return x; } else { return y; } } public static void main(String[] args){ Test t = new Test(); Object x = t.findLarger(123, "456"); } This code compiles and runs .In an IDE when I browse over the line Object x = ...  | Contact Us | Privacy Policy
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