Map Initialization Methods

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 in a map so that you can do something with them.

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