Java Language Maps Add multiple items
Example
We can use V put(K key,V value):
Associates the specified value with the specified key in this map (optional operation). If the map previously contained a mapping for the key, the old value is replaced by the specified value.
String currentVal;
Map<Integer, String> map = new TreeMap<>();
currentVal = map.put(1, "First element.");
System.out.println(currentVal);// Will print null
currentVal = map.put(2, "Second element.");
System.out.println(currentVal); // Will print null yet again
currentVal = map.put(2, "This will replace 'Second element'");
System.out.println(currentVal); // will print Second element.
System.out.println(map.size()); // Will print 2 as key having
// value 2 was replaced.
Map<Integer, String> map2 = new HashMap<>();
map2.put(2, "Element 2");
map2.put(3, "Element 3");
map.putAll(map2);
System.out.println(map.size());
Output:
3
To add many items you can use an inner classes like this:
Map<Integer, String> map = new HashMap<>() {{
// This is now an anonymous inner class with an unnamed instance constructor
put(5, "high");
put(4, "low");
put(1, "too slow");
}};
Keep in mind that creating an anonymous inner class is not always efficient and can lead to memory leaks so when possible, use an initializer block instead:
static Map<Integer, String> map = new HashMap<>();
static {
// Now no inner classes are created so we can avoid memory leaks
put(5, "high");
put(4, "low");
put(1, "too slow");
}
The example above makes the map static. It can also be used in a non-static context by removing all occurences of static.
In addition to that most implementations support putAll, which can add all entries in one map to another like this:
another.putAll(one);
