Collections (JJWT :: API 0.12.1 API)

java.lang.Object
- io.jsonwebtoken.lang.Collections

```
public final class Collections
extends Object
```
Utility methods for working with Collections, Lists, Sets, and Maps.

Method Summary

Methods
Modifier and Type	Method and Description
`static List`	`arrayToList(Object source)` Convert the supplied array into a List.
`static <T> Set<T>`	`asSet(Collection<T> c)` Returns the specified collection as a `Set` instance.
`static <T> Set<T>`	`concat(Set<T> c, T... elements)` Concatenate the specified set with the specified array elements, resulting in a new `LinkedHashSet` with the array elements appended to the end of the existing Set.
`static boolean`	`contains(Enumeration enumeration, Object element)` Check whether the given Enumeration contains the given element.
`static boolean`	`contains(Iterator iterator, Object element)` Check whether the given Iterator contains the given element.
`static boolean`	`containsAny(Collection source, Collection candidates)` Return `true` if any element in '`candidates`' is contained in '`source`'; otherwise returns `false`.
`static boolean`	`containsInstance(Collection collection, Object element)` Check whether the given Collection contains the given element instance.
`static <T> List<T>`	`emptyList()` Returns a type-safe immutable empty `List`.
`static <K,V> Map<K,V>`	`emptyMap()` Returns a type-safe immutable empty `Map`.
`static <T> Set<T>`	`emptySet()` Returns a type-safe immutable empty `Set`.
`static Class<?>`	`findCommonElementType(Collection collection)` Find the common element type of the given Collection, if any.
`static Object`	`findFirstMatch(Collection source, Collection candidates)` Return the first element in '`candidates`' that is contained in '`source`'.
`static Object`	`findValueOfType(Collection<?> collection, Class<?>[] types)` Find a single value of one of the given types in the given Collection: searching the Collection for a value of the first type, then searching for a value of the second type, etc.
`static <T> T`	`findValueOfType(Collection<?> collection, Class<T> type)` Find a single value of the given type in the given Collection.
`static boolean`	`hasUniqueObject(Collection collection)` Determine whether the given Collection only contains a single unique object.
`static <T,C extends Collection<T>> C`	`immutable(C c)` Null-safe factory method that returns an immutable/unmodifiable view of the specified collection instance.
`static <T> List<T>`	`immutable(List<T> list)` Shorter null-safe convenience alias for `Collections.unmodifiableList(List)` so both classes don't need to be imported.
`static <K,V> Map<K,V>`	`immutable(Map<K,V> m)` Shorter null-safe convenience alias for `Collections.unmodifiableList(List)` so both classes don't need to be imported.
`static <T> Set<T>`	`immutable(Set<T> set)` Shorter null-safe convenience alias for `Collections.unmodifiableSet(Set)` so both classes don't need to be imported.
`static boolean`	`isEmpty(Collection<?> collection)` Return `true` if the supplied Collection is `null` or empty.
`static boolean`	`isEmpty(Map<?,?> map)` Return `true` if the supplied Map is `null` or empty.
`static void`	`mergeArrayIntoCollection(Object array, Collection collection)` Merge the given array into the given Collection.
`static void`	`mergePropertiesIntoMap(Properties props, Map map)` Merge the given Properties instance into the given Map, copying all properties (key-value pairs) over.
`static <T> Collection<T>`	`nullSafe(Collection<T> c)` Returns a non-null collection, either `c` if it is not null, or `emptyList()` otherwise.
`static <T> Set<T>`	`nullSafe(Set<T> s)` Returns a non-null set, either `s` if it is not null, or `emptySet()` otherwise.
`static <T> List<T>`	`of(T... elements)` Returns a type-safe immutable `List` containing the specified array elements.
`static <T> Set<T>`	`setOf(T... elements)` Returns a type-safe immutable `Set` containing the specified array elements.
`static int`	`size(Collection<?> collection)` Returns the collection's size or `0` if the collection is `null`.
`static int`	`size(Map<?,?> map)` Returns the map's size or `0` if the map is `null`.
`static <A,E extends A> A[]`	`toArray(Enumeration<E> enumeration, A[] array)` Marshal the elements from the given enumeration into an array of the given type.
`static <E> Iterator<E>`	`toIterator(Enumeration<E> enumeration)` Adapt an enumeration to an iterator.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Method Detail
  - emptyList
```
public static <T> List<T> emptyList()
```
    Returns a type-safe immutable empty List.
    
    Type Parameters:
    T - list element type
    
    Returns:
    a type-safe immutable empty List.
  - emptySet
```
public static <T> Set<T> emptySet()
```
    Returns a type-safe immutable empty Set.
    
    Type Parameters:
    T - set element type
    
    Returns:
    a type-safe immutable empty Set.
  - emptyMap
```
public static <K,V> Map<K,V> emptyMap()
```
    Returns a type-safe immutable empty Map.
    
    Type Parameters:
    K - map key type
    V - map value type
    
    Returns:
    a type-safe immutable empty Map.
  - of
```
@SafeVarargs
public static <T> List<T> of(T... elements)
```
    Returns a type-safe immutable List containing the specified array elements.
    
    Type Parameters:
    T - list element type
    Parameters:
    elements - array elements to include in the list
    
    Returns:
    a type-safe immutable List containing the specified array elements.
  - asSet
```
public static <T> Set<T> asSet(Collection<T> c)
```
    Returns the specified collection as a Set instance.
    
    Type Parameters:
    T - collection element type
    Parameters:
    c - the collection to represent as a set
    
    Returns:
    a type-safe immutable Set containing the specified collection elements.
    Since:
    
    0.12.0
  - setOf
```
@SafeVarargs
public static <T> Set<T> setOf(T... elements)
```
    Returns a type-safe immutable Set containing the specified array elements.
    
    Type Parameters:
    T - set element type
    Parameters:
    elements - array elements to include in the set
    
    Returns:
    a type-safe immutable Set containing the specified array elements.
  - immutable
```
public static <K,V> Map<K,V> immutable(Map<K,V> m)
```
    Shorter null-safe convenience alias for Collections.unmodifiableList(List) so both classes don't need to be imported.
    
    Type Parameters:
    K - map key type
    V - map value type
    Parameters:
    m - map to wrap in an immutable/unmodifiable collection
    
    Returns:
    an immutable wrapper for m.
    Since:
    
    0.12.0
  - immutable
```
public static <T> Set<T> immutable(Set<T> set)
```
    Shorter null-safe convenience alias for Collections.unmodifiableSet(Set) so both classes don't need to be imported.
    
    Type Parameters:
    T - set element type
    Parameters:
    set - set to wrap in an immutable Set
    
    Returns:
    an immutable wrapper for set
  - immutable
```
public static <T> List<T> immutable(List<T> list)
```
    Shorter null-safe convenience alias for Collections.unmodifiableList(List) so both classes don't need to be imported.
    
    Type Parameters:
    T - list element type
    Parameters:
    list - list to wrap in an immutable List
    
    Returns:
    an immutable wrapper for list
  - immutable
```
public static <T,C extends Collection<T>> C immutable(C c)
```
    Null-safe factory method that returns an immutable/unmodifiable view of the specified collection instance. Works for List, Set and Collection arguments.
    
    Type Parameters:
    C - type of collection
    T - type of elements in the collection
    Parameters:
    c - collection to wrap in an immutable/unmodifiable collection
    
    Returns:
    an immutable wrapper for l.
    Since:
    
    0.12.0
  - nullSafe
```
public static <T> Set<T> nullSafe(Set<T> s)
```
    Returns a non-null set, either s if it is not null, or emptySet() otherwise.
    
    Type Parameters:
    T - type of elements in the set
    Parameters:
    s - the set to check for null
    
    Returns:
    a non-null set, either s if it is not null, or emptySet() otherwise.
    Since:
    
    0.12.0
  - nullSafe
```
public static <T> Collection<T> nullSafe(Collection<T> c)
```
    Returns a non-null collection, either c if it is not null, or emptyList() otherwise.
    
    Type Parameters:
    T - type of elements in the collection
    Parameters:
    c - the collection to check for null
    
    Returns:
    a non-null collection, either c if it is not null, or emptyList() otherwise.
    Since:
    
    0.12.0
  - isEmpty
```
public static boolean isEmpty(Collection<?> collection)
```
    Return true if the supplied Collection is null or empty. Otherwise, return false.
    
    Parameters:
    collection - the Collection to check
    
    Returns:
    whether the given Collection is empty
  - size
```
public static int size(Collection<?> collection)
```
    Returns the collection's size or 0 if the collection is null.
    
    Parameters:
    collection - the collection to check.
    
    Returns:
    the collection's size or 0 if the collection is null.
    Since:
    
    0.9.2
  - size
```
public static int size(Map<?,?> map)
```
    Returns the map's size or 0 if the map is null.
    
    Parameters:
    map - the map to check
    
    Returns:
    the map's size or 0 if the map is null.
    Since:
    
    0.9.2
  - isEmpty
```
public static boolean isEmpty(Map<?,?> map)
```
    Return true if the supplied Map is null or empty. Otherwise, return false.
    
    Parameters:
    map - the Map to check
    
    Returns:
    whether the given Map is empty
  - arrayToList
```
public static List arrayToList(Object source)
```
    Convert the supplied array into a List. A primitive array gets converted into a List of the appropriate wrapper type.
    A null source value will be converted to an empty List.
    
    Parameters:
    source - the (potentially primitive) array
    
    Returns:
    the converted List result
    See Also:
    Objects.toObjectArray(Object)
  - concat
```
@SafeVarargs
public static <T> Set<T> concat(Set<T> c,
                            T... elements)
```
    Concatenate the specified set with the specified array elements, resulting in a new LinkedHashSet with the array elements appended to the end of the existing Set.
    
    Type Parameters:
    T - set element type
    Parameters:
    c - the set to append to
    elements - the array elements to append to the end of the set
    
    Returns:
    a new LinkedHashSet with the array elements appended to the end of the original set.
  - mergeArrayIntoCollection
```
public static void mergeArrayIntoCollection(Object array,
                            Collection collection)
```
    Merge the given array into the given Collection.
    
    Parameters:
    array - the array to merge (may be null)
    collection - the target Collection to merge the array into
  - mergePropertiesIntoMap
```
public static void mergePropertiesIntoMap(Properties props,
                          Map map)
```
    Merge the given Properties instance into the given Map, copying all properties (key-value pairs) over.
    Uses Properties.propertyNames() to even catch default properties linked into the original Properties instance.
    
    Parameters:
    props - the Properties instance to merge (may be null)
    map - the target Map to merge the properties into
  - contains
```
public static boolean contains(Iterator iterator,
               Object element)
```
    Check whether the given Iterator contains the given element.
    
    Parameters:
    iterator - the Iterator to check
    element - the element to look for
    
    Returns:
    true if found, false else
  - contains
```
public static boolean contains(Enumeration enumeration,
               Object element)
```
    Check whether the given Enumeration contains the given element.
    
    Parameters:
    enumeration - the Enumeration to check
    element - the element to look for
    
    Returns:
    true if found, false else
  - containsInstance
```
public static boolean containsInstance(Collection collection,
                       Object element)
```
    Check whether the given Collection contains the given element instance.
    Enforces the given instance to be present, rather than returning true for an equal element as well.
    
    Parameters:
    collection - the Collection to check
    element - the element to look for
    
    Returns:
    true if found, false else
  - containsAny
```
public static boolean containsAny(Collection source,
                  Collection candidates)
```
    Return true if any element in 'candidates' is contained in 'source'; otherwise returns false.
    
    Parameters:
    source - the source Collection
    candidates - the candidates to search for
    
    Returns:
    whether any of the candidates has been found
  - findFirstMatch
```
public static Object findFirstMatch(Collection source,
                    Collection candidates)
```
    Return the first element in 'candidates' that is contained in 'source'. If no element in 'candidates' is present in 'source' returns null. Iteration order is Collection implementation specific.
    
    Parameters:
    source - the source Collection
    candidates - the candidates to search for
    
    Returns:
    the first present object, or null if not found
  - findValueOfType
```
public static <T> T findValueOfType(Collection<?> collection,
                    Class<T> type)
```
    Find a single value of the given type in the given Collection.
    
    Type Parameters:
    T - the generic type parameter for type
    Parameters:
    collection - the Collection to search
    type - the type to look for
    
    Returns:
    a value of the given type found if there is a clear match, or null if none or more than one such value found
  - findValueOfType
```
public static Object findValueOfType(Collection<?> collection,
                     Class<?>[] types)
```
    Find a single value of one of the given types in the given Collection: searching the Collection for a value of the first type, then searching for a value of the second type, etc.
    
    Parameters:
    collection - the collection to search
    types - the types to look for, in prioritized order
    
    Returns:
    a value of one of the given types found if there is a clear match, or null if none or more than one such value found
  - hasUniqueObject
```
public static boolean hasUniqueObject(Collection collection)
```
    Determine whether the given Collection only contains a single unique object.
    
    Parameters:
    collection - the Collection to check
    
    Returns:
    true if the collection contains a single reference or multiple references to the same instance, false else
  - findCommonElementType
```
public static Class<?> findCommonElementType(Collection collection)
```
    Find the common element type of the given Collection, if any.
    
    Parameters:
    collection - the Collection to check
    
    Returns:
    the common element type, or null if no clear common type has been found (or the collection was empty)
  - toArray
```
public static <A,E extends A> A[] toArray(Enumeration<E> enumeration,
                          A[] array)
```
    Marshal the elements from the given enumeration into an array of the given type. Enumeration elements must be assignable to the type of the given array. The array returned will be a different instance than the array given.
    
    Type Parameters:
    A - the element type of the array that will be created
    E - the element type contained within the enumeration.
    Parameters:
    enumeration - the collection to convert to an array
    array - an array instance that matches the type of array to return
    
    Returns:
    a new array of type A that contains the elements in the specified enumeration.
  - toIterator
```
public static <E> Iterator<E> toIterator(Enumeration<E> enumeration)
```
    Adapt an enumeration to an iterator.
    
    Type Parameters:
    E - the type of elements in the enumeration
    Parameters:
    enumeration - the enumeration
    
    Returns:
    the iterator

Class Collections

Method Summary

Methods inherited from class java.lang.Object

Method Detail

emptyList

emptySet

emptyMap

of

asSet

setOf

immutable

immutable

immutable

immutable

nullSafe

nullSafe

isEmpty

size

size

isEmpty

arrayToList

concat

mergeArrayIntoCollection

mergePropertiesIntoMap

contains

contains

containsInstance

containsAny

findFirstMatch

findValueOfType

findValueOfType

hasUniqueObject

findCommonElementType

toArray

toIterator