TreeMap
In this chapter you will learn:
TreeMap class
The TreeMap class extends AbstractMap
and implements the NavigableMap interface.
It creates maps stored in a tree structure.
A tree map guarantees that its elements will be sorted in an order.
TreeMap is a generic class that has this declaration:
class TreeMap<K, V>
- K specifies the type of keys
- V specifies the type of values.
The following TreeMap constructors are defined:
TreeMap( )constructs an empty tree map.TreeMap(Comparator<? super K> comp)constructs an empty tree-based map using the Comparator comp.TreeMap(Map<? extends K, ? extends V> m)initializes a tree map with the entries from m.TreeMap(SortedMap<K, ? extends V> sm)initializes a tree map with the entries from SortedMap.
TreeMap has no methods beyond those specified by the
NavigableMap interface and the AbstractMap class.
Put TreeMap to work
The following code sorts a map's entries according to the natural ordering of their String-based keys
import java.util.Map;
import java.util.TreeMap;
//from ja v a 2 s.c o m
public class Main {
public static void main(String[] args) {
Map<String, Integer> msi = new TreeMap<String, Integer>();
String[] fruits = { "apples", "pears", "grapes", "bananas", "kiwis" };
int[] quantities = { 10, 15, 8, 17, 30 };
for (int i = 0; i < fruits.length; i++){
msi.put(fruits[i], quantities[i]);
}
for (Map.Entry<String, Integer> entry : msi.entrySet()){
System.out.println(entry.getKey() + ": " + entry.getValue());
}
}
}
The output:
From the output we can see that the key-value pairs are ordered by the key value.
Next chapter...
What you will learn in the next chapter:
- How to get first key in TreeMap
- How to get the last key in a TreeMap
- How to get key relative a give value
- How to get least key value relative to a key value
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