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Java.util package provides a TreeSet class which is a NavigableSet implementation based on a TreeMap. The elements are ordered using their natural ordering, or by a Comparator provided at set creation time, depending on which constructor is used. The class guarantees that the Map will be in ascending key order and backed by a TreeMap.
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Java.util package provides a EnumSet class which is a specialized Set implementation for use with enum types. All of the elements in an enum set must come from a single enum type that is specified, explicitly or implicitly, when the set is created. Enum sets are represented internally as bit vectors. This representation is extremely compact and efficient. Null elements are not permitted. Attempts to insert a null element will throw NullPointerException.
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Java.util package provides a Calendar class which represents a specific instant in time, with millisecond precision.
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Java.util package provides a GregorianCalendar class which is a concrete subclass of Calendar and provides the standard calendar system used by most of the world.
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Java.util package provides a Random class. An instance of this class is used to generate a stream of pseudorandom numbers. The class uses a 48-bit seed, which is modified using a linear congruential formula. The algorithms implemented by class Random use a protected utility method that on each invocation can supply up to 32 pseudorandomly generated bits.
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Java.util package provides a Date class which represents a specific instant in time, with millisecond precision.
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Java.util package provides a UUID class which represents an immutable universally unique identifier (UUID). A UUID represents a 128-bit value. It is used for for creating random file names, session id in web application, transaction id etc. There are four different basic types of UUIDs: time-based, DCE security, name-based, and randomly generated UUIDs.
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Java.util package provides a Dictionary class which is the abstract parent of any class, such as Hashtable, which maps keys to values. Every key and every value is an object. In any one Dictionary object, every key is associated with at most one value. Given a Dictionary and a key, the associated element can be looked up. Any non-null object can be used as a key and as a value.
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A Hashtable models and implements the Map interface. This implementation provides all of the optional map operations, and permits null values and the null key. A HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls. This class makes no guarantees as to the order of the map. It does not guarantee that the order will remain constant over time.
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A Hashtable models and implements the Map interface. This implementation provides all of the optional map operations, and permits null values and the null key. A HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls. This class makes no guarantees as to the order of the map. It does not guarantee that the order will remain constant over time.
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Java.util package provides a EnumMap class which is a specialized Map implementation for use with enum type keys. All of the keys in an enum map must come from a single enum type that is specified, explicitly or implicitly, when the map is created.
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Java.util package provides a Hashtable class which implements hash table and maps keys to value. Any non-null object can be used as a key or as a value. To successfully store and retrieve objects from a hashtable, the objects used as keys must implement the hashCode method and the equals method.
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A HashSet class implements the Set interface, backed by the a Hashtable interface (actually a HashMap instance). This class makes no guarantees as to the iteration order of the set. It does not guarantee that the order will remain constant over time. The class permits the null element.
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Java.util package provides a Scanner class. A simple text scanner parse primitive types and strings using regular expressions. A Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace. The resulting tokens may then be converted into values of different types using the various next methods.
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Java.util package provides a vector class which models and implements vector data structure. A vector is a sequence container implementing array that can change in size. Unlike array, the size of a vector changes automatically when elements are appended or deleted. It is similar to ArrayList, but with two differences:

Vector is synchronized.
Vector contains many legacy methods that are not part of the collections framework.
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Java.util package provides an ArrayList class which provides resizable-array implementation of the list interface. It implements all optional list operations and permits all elements including null. Along with this, the class provides methods to manipulate the size of the array that is used internally to store the list. This class is almost equivalent to Vector class except the implementation is not synchronized.
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Java Utility Library - ArrayDeque Tutorial
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Java Utility Library - LinkedList Tutorial