Type 1 « Generic « Java Collection Q&A

1. Should Java raw types be deprecated?    stackoverflow.com

Should a future release of Java deprecate the use of raw types to force the migration to generics? I could also see having raw types not allowed by default but allowing ...

2. Type mismatch with generics    stackoverflow.com

Here's an interface:

public interface Foo<T> extends Comparable<Foo<T>>  {
   ...
}

public class Bar extends Something implements Foo<Something> {
    public Vector<Foo<Bar>> ...

3. Concrete vs. Bounded Parameterized Type when designing a typesafe API    stackoverflow.com

I would like to hear from you guys on how do you decide when you should be using concrete parameterized type vs. bounded parameterized type when designing API, esp. (that I ...

4. java bounded generic type definition    stackoverflow.com

What's the difference between the following type definitions

<E extends Number>

<? extends Number>

5. Java Generics - difficulty enforcing strong type checking    stackoverflow.com

Here's my code:

public class Sequence<T> {

    protected List<T> sequence = new ArrayList<T>();

    public Matrix<OrderedPair<T, ?>> createCartesianProduct(Sequence<?> secondSequence) {
     Matrix<OrderedPair<T, ?>> result ...

6. Is it possible to use a primitive type (int) in as a generic type in Java?    stackoverflow.com

Specifically, with a SortedMap<Vector<String>, int> I get "dimensions expected after this (int) token." Help!

7. Java: Specifying generics on Type AND Implementation    stackoverflow.com

Most references I've seen, and my IDE's code completion all have my specifying a Generic type on both a variables type and its implementation eg.

List<String> string = new ArrayList<String>();

8. Javac flag to disallow raw types?    stackoverflow.com

Is there any Java compiler flag that one can pass to tell the compiler to disallow the use of raw types? That is, for any generic class, let the compiler force ...

9. Type safety, Java generics and querying    stackoverflow.com

I have an interesting situation and I'm wondering if there is a better way to do this. The situation is this, I have a tree structure (an abstract syntax tree, ...

10. Which type cannot be used as Generics    stackoverflow.com

Which type cannot be used as generics?

11. Java Raw Type and generics interaction    stackoverflow.com

If I have a Stack class

class Stack<E> {}

12. What is Type called?    stackoverflow.com

What is

Type<Type> type;

Type type;

13. Generics: Type as variable?    stackoverflow.com

In order to be able to substitute a specific implementation, it is commonly known to write

List<AnyType> myList = new ArrayList<AnyType>();

ArrayList<AnyType> myList = new ArrayList<AnyType>();

14. Supporting covariant type conversions in Java    stackoverflow.com

The Java type system supports only invariant types. So a List<String> is not an List<Object>. A List<String> is not a List<Object> as it is not valid to insert an Integer into ...

15. Java generics and simple types    stackoverflow.com

I was trying to write a generic class, that could operate on any simple type (int, float, etc.). I wanted to avoid repeating the same function several times, with changing the ...

16. isAssignableFrom with reference and primitive types    stackoverflow.com

I'd like to get a better understanding of the isAssignableFrom behaviour in Java between primitive and reference types. Eg:

System.out.println(boolean.class.isAssignableFrom(Boolean.class)); // false
System.out.println(Boolean.class.isAssignableFrom(boolean.class)); // false

boolean primitive;
Boolean referenceType = true;
primitive = referenceType;
System.out.println(primitive); // true

17. Java Generics - vanishing type information?    stackoverflow.com

OK - I know that Java generics can be a minefield for the unwary, but I just came across a non-intuitive (to me anyway) behavior that I was wondering if anyone ...

18. Java generics - retrieve type    stackoverflow.com

public Interface Foo<T extends Colors>{...}

public Class FooImpl implements Foo<Green>{..}

19. Java Generic Type question    stackoverflow.com

i just have a quick question about the Generic Type. i have an interface class

public interface myInterface<T> {
    T add();
}

public class interfaceImp<T> implements myInterface
{
   ...

20. Knowing type of generic in Java    stackoverflow.com

I have a generic class, says :

MyClass<T>

void MyMethod()
{

    if (T == ...

21. generics multiple types    stackoverflow.com

Defining a method as

myMethod(Object... obj){}

22. How to create a generic XSD type    stackoverflow.com

I have a java application where i can map a XSD type to another with same type. Now i have requirement to have one anyType xsd to which i can map ...

23. Java generic type    stackoverflow.com

When I have an interface

public interface Foo<T> {
    T someMethod();
}

24. toString() a generic type in Java    stackoverflow.com

How can I print the type of a generic java type? Reflection? Any tricks?

public class Foo<K> {

    private K element;

    @Override
    public String ...

25. Java Generics Hell - Passing in this but it wants type T    stackoverflow.com

I'm currently developing a lightweight, general-purpose simulation framework. The goal is to allow people to subclass the Simulation and Scenario objects for their domain-specific needs. Generics seemed like an appropriate way ...

26. Why don't Generics support primitive types?    stackoverflow.com

Why Generics (in Java) works with the objects but not with primitive types? For example

Gen<Integer> inum = new Gen<Integer>(100); // works fine, but  
Gen<int> inums = new Gen<int>(100); // ...

27. What is a raw type and why shouldn't we use it?    stackoverflow.com

Questions:

• What are raw types in Java, and why do I often hear that they shouldn't be used in new code?
• What is the alternative if we can't use raw types, and how ...

28. Java generics - getting the type    stackoverflow.com

Duplicate: Instantiating generics type in java

public T create_an_instance_of<T>(){
  ...

29. is there some lightweight tecnique for adding type safety to identifier properties?    stackoverflow.com

After using C++ I got used to the concept of Identifier which can be used with a class for the type, provides type safety and has no runtime overhead (the actual ...

30. Java generics and varargs    stackoverflow.com

I'd like to implement a function with both generics and varargs.

public class Question {
    public static <A> void doNastyThingsToClasses(Class<A> parent, Class<? extends A>... classes) {
    ...

31. Java generics infering type    stackoverflow.com

my IDE generates a warning when i use the following code:

aMethod(List.class);

32. Taming the type checker in Java Generics    stackoverflow.com

I thought I understood Generics pretty well, but apparently I didn't. Here is the test case of the problem:

import java.util.ArrayList;

class Job<J extends Job<J,R>, R extends Run<J,R>> {}
class Run<J extends Job<J,R>, R extends ...

33. Is there any reason I shouldn't ignore generic types in the concrete types?    stackoverflow.com

Generics in Java is noisy sometimes. The parameterized types are thrown out by the compiler anyway after compile, so my question is, is there really any drawbacks in ignoring them, as ...

34. Why null was called "a subtype of every reference type"?    stackoverflow.com

Guys, could any one give a logical explanation of phrase I met in this book:

You may find it helpful to think of ? extends T as containing ...

35. Incorrect generic type reported -- why?    stackoverflow.com

Why doesn't this work?

public class FooImpl implements Foo { /* ... */ }

public class Main {
    public static <T> Collection<T> getList(Class<? extends T> itemClass) { /* ... */ ...

36. How is the generic type getting inferred here?    stackoverflow.com

public static void main(String[] args) {
    Map<String, Map<Long, List<String>>> map = getHashMap();
}

static <K,V> Map<K,V> getHashMap()
{
    return new HashMap<K, V>();
}

37. Java Generic / Type Dispatch Question    stackoverflow.com

Consider the following program:

import java.util.List;
import java.util.ArrayList;

public class TypeTest {

    public static class TypeTestA extends TypeTest {

    }

    public static class TypeTestB extends ...

38. De-Serializing a generic (but Serializable) type    stackoverflow.com

I'm wondering if it's possible to de-serialize a generic type into an instance of that type. If it is possible, does Java take into account the generic type's custom de-deserialization (if ...

39. Java Generic Type Variables    stackoverflow.com

my question is about type variables used in generic classes and methods,
why can't we do something like this T = new T(); "Construct an object of the type variable"
i know that ...

40. Substitution for generic type's field    stackoverflow.com

I have generic structure and I need to search using various generic type's attributes. Let's think of following implementation:

public class Person {
  private int id;
  private String name;
  // ...

41. Java. How to prohibit usage of raw generic type?    stackoverflow.com

Hi I'm writing the reporting system and want to make end-user specify type if he extends my class.

class A <T extends C>
{...}

class B extends A // Compile error
{...}

class B extends A<D> ...

42. Using Generics with Abstract Data Types in Java    stackoverflow.com

For a CS class I need to solve an assigned problem using three data structures: Queue, PriorityQueue, and Stack. I wanted to write a single solution to the problem using ...

43. Java Storing Conditions By Generic Type    stackoverflow.com

I've been reading Effective Java and decided to try to put some of what I've learned into action. I'm trying to effectively create a Multimap<?, Condition<?> > where the ...

44. JDK7: new features related to type variables?    stackoverflow.com

I remember to have read about a new feature of JDK7 (now also supported by the Netbeans editor, yet only in current trunk builds). This tiny feature wouldn't produce a warning anymore ...

45. programmatically determine generic type    stackoverflow.com

apologies if this is a duplicate. Is there any way to determine what generic type a class is? ie I want to know what T is....

public void doSomething(SomeClass<T> thing)
{
    Class<T> ...

46. How to extract a Generic type from arg    stackoverflow.com

I have a method signature that looks like

public void (Foo<T> foo)

47. Generic type bounded by another generic    stackoverflow.com

Suppose I have this:

interface Shape {}
interface Square extends Shape {}
interface Circle extends Shape {}

interface ShapeBuilder<S extends Shape> {}

class ShapeBuilderFactory<SB extends ShapeBuilder> {
    SB<Square> getSquareBuilder(){...}
 ...

48. dynamic binding with generic type    stackoverflow.com

i need to bind dynamic a parametic type (List) but i dont get it right... here is an overview of my classes:

public abstract interface SettingsField<A> extends Window

49. Generic types in Java    stackoverflow.com

Is it right that this code

List<Integer> test2 = new ArrayList<Integer>();
test2.add(343);
int x2 = test2.get(0);

List test = new ArrayList();
test.add(343);
int x = (Integer)test.get(0);

50. Is it possible to test the type in a generic function?    stackoverflow.com

I would like to make a generic function that deserializes a byte array into a type specified by the caller. I feel that a really intuitive way to call such a function ...

51. How to use a generic factory for generic type without warnings?    stackoverflow.com

I have a factory method like

public static <T> Something<T> create(Class<T> clazz) {
    return new Something<T>(clazz);
}

Something<String> something1 = Something.create(String.class);

52. Using a generic type with Gson    stackoverflow.com

I am trying to create a generic class for use with Google Gson. I've created the class GsonJsonConverterImplementation<T>. This class has the following method:

public T deserialize(String jsonString) {
  ...

53. How to compare generics of same type?    stackoverflow.com

I'm trying to compare two subclasses of Number inside a class with generics. In the code below, I'm trying to compare Number objects inside an instance of Datum. How do I enforce ...

54. Why do I get a Type safety warning here? (generics)    stackoverflow.com

I lately wanted to learn more about generic methods and created several examples, but the following type safety is not clear to me. Here an example:

public class GeneralMethod
{
  public static ...

55. limited generic type    stackoverflow.com

I'm trying to create a generic class that accepts only two types (i.e., Integers and Doubles), as if I would make the class with only Double type, I would be wasting ...

56. Java generics void/Void types    stackoverflow.com

I am implementing a ResponseHandler for the apache HttpClient package, like so:

new ResponseHandler<int>() {
    public int handleResponse(...) {
        // ... code ...

57. Java generics type mismatch    stackoverflow.com

I have an abstract class defined as:

public abstract class TCV<T extends MF> {
    public Map<String, MVR<T>> operation() {
        ...
   ...

58. Java Generics - Check type of T    stackoverflow.com

I am using a method like this

private static <T> void setPreference(String key, T value)
{
    SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(Controller.getContext());

    SharedPreferences.Editor editor = prefs.edit();

    ...

59. java generic parameterized type    stackoverflow.com

Sorry for this simple question In this class

class GenericTest{
    static <T> List<T> getList(List<T> list){
        return list;
    }
}

60. Why do raw types in one place cause generic callsites somewhere else to be treated as raw?    stackoverflow.com

Consider this example:

import java.util.*;

class Foo<T> {
  public int baz(List<String> stringlist) { return 1; }
  public int baz(ArrayList<Object> objectlist) { return 2; }

  public static void main(String[] args) {
 ...

61. Inferred generic types and the backtick in JDK7    stackoverflow.com

I have been making my way through the Java Tutorial and have been reading about generic type inference in JDK7. I came across the following syntax...

class MyClass<X> {
 ...

62. Help with Java generics and bounded types    stackoverflow.com

I have a wrapper class for ConcurrentMap like the following:

public MapWrapper<K, V> implements ConcurrentMap<K, V> {

    private final ConcurrentMap<K, V> wrappedMap;

    ...
    ...

63. Java: generics type    stackoverflow.com

Class B extends from class A, and G is generics class. Now -

G<X> g = new G<B>();

? extends A

? super B

64. Java - generic type    stackoverflow.com

For this question, we assume that is possible to extend the class String in java. In the next code:

T getId ( ) ;
void setId (T t ) ;
}
public class Person implements ...

65. Using the Java Guava library, how to create a ImmutableSortedSet using a Builder?    stackoverflow.com

I'm sure this is a very simple question but please take a look at the code sample below:

final ImmutableSortedSet<String> notOk = ImmutableSortedSet.naturalOrder().build();         
final ...

66. Java containers of generic types    stackoverflow.com

I am preparing for an exam and one of the codes we were given by professor is obscure to me:

public class Z {

    static java.util.LinkedList<? extends Object> a ...

67. Checking generic type    stackoverflow.com

The Java Collections interfaces (for example, List or Set) define the contains method to accept any Object.

 public boolean contains(Object o)

68. Initializing variable. I don't know their type [java]    stackoverflow.com

class pair<U,V>{
U first;
V second;
public pair() {
    first = new U(); //error
    second = new V(); //error
}   
public pair(U f,V s){
    ...

69. Java type safety warning    stackoverflow.com

I'm trying to make an array of vectors like this:

Vector<String>[] wordList = new Vector[29];
for (int i = 0; i < wordList.length; i++) {
  wordList[i] = new Vector<String>(100);
}

70. Jackson and generic type reference    stackoverflow.com

I want to use jackson json library for a generic method as follows:

public MyRequest<T> tester(){
  TypeReference<MyWrapper<T>> typeRef = new TypeReference<MyWrapper<T>>();  
  MyWrapper<T> requestWrapper = (MyWrapper<T>) JsonConverter.fromJson(jsonRequest, typeRef);
  ...

71. Generic Type toArray and asList    stackoverflow.com

I am trying to understand generics and I purposely want to generate a classcastexception, however, i instead get an arraystoreexception on the first attempt.

    static <E> E reduce(List<E> ...

72. why java generics have to erase the type information?    stackoverflow.com

Java's generics would erase the type information after the source code was compiled. And i guess the "erase" is necessary because java only keep one copy of class no matter what ...

73. Is it possible to write a Java generics expression that allows a subtype of a type and the type itself?    stackoverflow.com

Given the following situation it's only possible to write a model handler which works on SpecificModel, it's not possible to have a model handler which handles only models. But when we ...

74. Java Generics Bound mismatch with a raw type    stackoverflow.com

I have a super class with a signature like

public abstract class Foo<C extends Comparable<? super C>>{..}

75. Deserialize generic type with XStream    stackoverflow.com

I'm trying to use XStream to deserialize a xml response to a class that has a generic type field. For example I have class Response

class Response<T extends BaseDTO>{
    int ...

76. Java - initiate generic variable with no generic type;    stackoverflow.com

Could you please explain the difference between these declarations :

List<Number> test = new ArrayList<Number>();
List<Number> test1 = new ArrayList();
test.add(new Integer(10));
test1.add(new Integer(10));
//test.add(new Object());
//test1.add(new Object());

77. How can I store Java types, allowing only some specific ones?    stackoverflow.com

Lets assume I want to have a class that acts a descriptor for records, where each record has a set of attributes. Each attribute has a unique name and should have a ...

78. Dynamic Generic Typing in Java    stackoverflow.com

If I have a class using generic type such as

public class Record<T> {
    private T value;

    public Record(T value) {
     ...

79. Is there a way to refer to the current type with a type variable?    stackoverflow.com

suppose I'm trying to write a function to return an instance of the current type. Is there a way to make T refer to the exact subtype (so T should refer ...

80. Java : Question regarding raw types and unbounded wild card characters in Generics    stackoverflow.com

I am reading the chapter on Generics in Effective Java. Help me understand difference between Set, Set<?> and Set<Object>? The following paragraph is taken from the book.

As a quick review, ...

81. ServiceLoader where type parm is itself generic    stackoverflow.com

class ServiceLoader<S> implements Iterable<S> {
    // ...
}

interface Foo<T> {
    // ...
}

class FooRepository {
    void add(Iterable<Foo<?>> foos) {
      ...

82. Java generics to support only predefined datatypes    stackoverflow.com

I'd like to use define a generic class in java, that can only be instantiated using my custom data types that all share the same base class. Is it possible to ...

83. How to deserialize JSON with GSON into corresponding generic Java types?    stackoverflow.com

I want to deserialize a JSON object (using GSON, because I already use it for searializing objects) to a general Map of type Map<String, Object>. It should create Objects of types ...

84. Java: get generic type    stackoverflow.com

I'm writing a Java wrapper for c++ and would like to use a generic class to wrap a c++ template. Therefore I'd like to get the generic type as String so ...

85. Java code compiles but yields IllegalAccessError    stackoverflow.com

In the code below, I give two main classes - TestWorks, and TestCompilesButFails. I'm not sure I understand the failure - it would appear that the Arrays.asList() expression is being given ...

86. Generics Type issue    stackoverflow.com

ArrayList<Integer> arrI = new ArrayList<Integer>();
ArrayList arrO = arrI; // Warning
/*  It is ok to add a String as it is an ArrayList of Objects
    but the JVM ...

87. How to get type of generic    stackoverflow.com

Possible Duplicate:
How to determine the class of a generic type?
How to obtain class instance generic argument type

88. Java deserialization of generic type with Gson    stackoverflow.com

I'm trying to deserialize some generic type. It works nice, but I would like to swap this peace of code out to a method.

Type listType = new TypeToken<TestResult<MyObject>>(){}.getType();
TestResult<MyObject> result = new ...

89. Parameterized Types / Generics    coderanch.com

Trying to create a static factory method of a parameterized type to be passed to the class of the objects that the factory is creating, but I'm unable to access the type parameters (compile-time error) because the method is static. Is it possible to pass the type parameter to the static method? The following source attempts to demonstrate what I'm trying ...

90. Type of Generic    coderanch.com

No, you can't. Generics are meaningful only at the source code level. They are not preserved in the class file. So there is no way by reflection to get information about generics from the compiled class. This is called "erasure." The reason for it is to preserve binary compatibility with older compiled code that does not use generics. Geoffrey

91. generics - incompatible types    coderanch.com

Map.Entry is an interface, hence, Map.entrySet() actually implements a new Map.Entry. Then, you're a actually receiving and not Map.Entry itself. Actually, reviewing the Tiger source code I discovered that HashMap has static nested class named Entry which hides that declard in the Map interface. This static nested class named Entry implements Map.Entry. At least thats what I think. ...

92. Generic types    coderanch.com

If you're referring to not having to cast to/from the Object then no. In order to use generics they must have a common type and casting to/from that type is the only thing you can avoid. I.e. You can't do Color c = vector.get(1) with a Vector

93. References to generic type Set E should be parameterized    coderanch.com

94. Dynamic Generic Type    coderanch.com

I'm trying to create a generic map with type specified at runtime and its being a pain. The following does not compile: final Type type = ... some type or class final Map map = new HashMap(); I've tried replacing the Type reference with Class, but no luck. The compiler does not recognize type in . Any suggestions? If there isn't ...

95. Generics type safety    coderanch.com

Hi I was trying out some generics in my code. I understand that i cant get away without a warning if i dont specify the type of the collection in 1.5. This is my code and it gives a warning that reads like "Type safety: The expression of type List needs unchecked conversion to conform to List". List vehicleYearList = new ...

96. Generics :Why type variables are not bound    coderanch.com

97. Generics - Bounded Parameterized Types    coderanch.com

98. Generic Java, Type not bounded    coderanch.com

Dear guys, I have declared LinkedList LL = new LinkList (); in my main class. Under my class Customer, I have a compareTo method too. I get an error on Type parameter customer is not within its bound. I believe the problem lies with the bold portion of the code which sorts the node. Can somebody guide me please? Thank in ...

99. Generics: Capture two types at once    coderanch.com

100. Generics with two types    coderanch.com

I have written the following code , to check what is the incoming object and add it in the collection but, i get an error given below class Employee{ } class BankAcount{ } class GenericClass{ UseT1 t1; UseT2 t2; ArrayList al; GenericClass(UseT1 t1,UseT2 t2){ this.t1 = t1; this.t2 = t2; } public UseT1 getT1() { return t1; } public void setT1(UseT1 ...