Android (java) Learning Note 102:map Collection features overview

Last Update:2015-06-05 Source: Internet

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The following code introduces the map collection:<pre>1 packagecn.itcast_01;2 3 Importjava.util.HashMap;4 Importjava.util.Map;5 6 /*7 * As a student, according to the number to distinguish between different students, then assuming I now know the Student's school number, I have to according to the number of students to obtain the name of the student, how can I do?8 * If we use the previously explained set, we can only use the number and student name as a member of the object, and then store the entire object, in the future, when the traversal, judge, get the corresponding Name. 9 * but, If I can take the Student's name out, do I still need to find it by number?Ten * For our current needs: just know the number, just want to know the Student's name, Java provides a new set of Map. one * By looking at the api, we know that one of the biggest features of the map collection is that it can store elements of Key-value Pairs. This is the time to store the requirements above and we can do this . a * School Number 1 Name 1 - * School Number 2 Name 2 - * School Number 3 name 3 the * School Number 2 (no) name 4 - * School Number 4 name 4 - * Features of the map collection: - * The object that maps the key to a Value. A map cannot contain duplicate keys, and each key can be mapped to at most one Value. + * - * What are the differences between the map collection and the collection collection? + * The Map collection storage elements are paired, and the keys of the map collection are unique and the values are Repeatable. This can be understood as: couples a * The collection Collection storage element is unique, and the collection son set is the only one, and the list is Repeatable. This can be understood as: bachelor (11.11) at * - * Note: - * The data structure value of the map collection is valid for the key, independent of the value - * Hashmap,treemap will Speak. - * The data structure of the collection collection is valid for the element - * in * Overview of the features of the map collection: - * 1: Add features to * V put (K key,v value): add Element. Does this actually have another function? not to tell you, wait to speak + * If the key is stored for the first time, the element is stored directly, returning null - * If the key does not exist for the first time, replace the previous value with a value and return the previous value the * 2: Delete function * * Void Clear (): removes all Key-value pair elements $ * V Remove (Object key): deletes the key value pair element according to the key, and returns the valuePanax Notoginseng * 3: Judging function - * Boolean ContainsKey (Object key): determines whether the collection contains the specified key the * Boolean Containsvalue (Object value): determines whether the collection contains the specified value + * Boolean IsEmpty (): determines whether the collection is empty, v indicates a generic type a * 4: Get features the * set<map.entry<k,v>> EntrySet ():??? + * V get (Object key): Gets the value according to the key - * set<k> KeySet (): Gets the collection of all the keys in the collection $ * collection<v> values (): Gets the collection of all values in the collection $ * 5: length function - * int size (): Returns the logarithm of the key-value pairs in the collection - */ the public classMapdemo { - public Static voidmain (string[] Args) {Wuyi //to Create a Collection object themap<string, string> map =Newhashmap<string, string>(); - wu //adding elements - //V put (K key,v value): adds an element. Does this actually have another function? not to tell you, wait to speak about //System.out.println ("put:" + map.put ("article", "Mai")); $ //System.out.println ("put:" + map.put ("article", "rotten")); - -Map.put ("deng chao", "sun li"); -Map.put ("huang xiaoming", "angelababy yang"); aMap.put ("jay chou", "jolin Tsai")); +Map.put ("jacky Lau wei", "yang mi"); the - //void Clear (): removes all Key-value pair elements $ //map.clear (); the the //V Remove (Object key): deletes the key-value pair element according to the key, and returns the value the //System.out.println ("remove:" + map.remove ("huang xiaoming")); the //System.out.println ("remove:" + map.remove ("Huang")); - in //Boolean ContainsKey (Object key): determines whether the collection contains the specified key the //System.out.println ("containskey:" + map.containskey ("huang xiaoming")); the //System.out.println ("containskey:" + map.containskey ("Huang")); about the //Boolean IsEmpty (): determines whether the collection is empty the //System.out.println ("isEmpty:" +map.isempty ()); the + //int size (): Returns the logarithm of the key-value pairs in the collection -System.out.println ("size:" +map.size ()); the Bayi //Output Collection name theSystem.out.println ("map:" +map); the } -}</pre>Android (java) Learning Note 102:map Collection features overview

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