Initialisation of Map:
Map<Integer, String> m = new Map<Integer, String>{5=>’Kalpana’};
m.put(1, ‘Bhavna’);
m.put(2, ‘Sapna’);
m.put(3, ‘Divya’);
m.put(4, ‘Bhavya’);
m.put(2, ‘Divya’); // this will override previous valueMap of List:
Map<Integer, List<Integer>> m = new Map<Integer, List<Integer>>();
m.put(1, new List());Methods of Map:
| put(key,value) | Associates the specified value with the specified key in the map. | Map<Integer,String> m = new Map<Integer,String>(); m.put(1, ‘Bhavna’);m.put(2, ’Sapna’); System.debug(s);//(1=‘Bhavna’,2=’Sapna’) |
| putAll(map) | Copies all of the mappings from the specified map to the original map. | Map<Integer,String> n = new Map<Integer,String>(); n.put(3, ’Bhavya’); n.put(4, ‘Divya’); m.putAll(n); System.debug(m);// (1=‘Bhavna’,2=’Sapna’ 3=’Bhavya’,4=’Divya’) |
| get(key) | Returns the value to which the specified key is mapped, or null if the map contains no value for this key. | System.debug(m.get(1)); // ‘Bhavna’ System.debug(m.get(2)); // ’Sapna’ System.debug(m.get(3)); // ’Bhavya’ System.debug(m.get(4)); // ’Divya’ |
| values() | Returns a list that contains all the values in the map. | List<String> l = new List<String>(); l = m.values(); System.debug(l);// (‘Bhavna’,’Sapna’,’Bhavya’,’Divya’) |
| clone() | Makes a duplicate copy of the map. | Map<Integer,String> o = new Map<Integer,String>(); o = m.clone(); System.debug(o);// (1=‘Bhavna’,2=’Sapna’ 3=’Bhavya’,4=’Divya’) |
| keySet() | Returns a set that contains all of the keys in the map. | System.debug(m.keySet()); // (1,2,3,4) |
| containsKey(key) | Returns true if the map contains a mapping for the specified key. | Boolean result1 = m.containsKey(3); System.debug(result1); // true Boolean result2 = m.containsKey(6); System.debug(result2); // false |
| isEmpty() | Returns true if map has 0 key. | Boolean result = m.isEmpty(); System.debug(result); // false |
| size() | Returns the number of key-value pairs in the map. | System.debug(m.size()); // 4 |
| remove(key) | Removes the mapping for the specified key from the map, if present, and returns the corresponding value. | m.remove(4); System.debug(m);//(1=‘Bhavna’,2=’Sapna’3=’Bhavya’) |
| clear() | Removes all of the key-value mappings from the map. | m.clear(); |
Note: Maps are used frequently to store records that you want to process or as containers for lookup data. It is very common to query for records and store them on a map so that you can do something with them.
