TreeMap(Java Collections)
An object of Map represents a group of objects, each of which is associated with a key. Like HashMap, TreeMap allows us to store values associated with the keys. A Map cannot contain duplicate keys. You can get the object from a Map using a key.TreeMap provides a guarantee of ordering(ascending, natural or provided) as TreeMap implements SortedMap.TreeMap does not allow null key but null values are allowed. TreeMap offers logarithmic time access for the general method to get, put and contains values.
Example
import java.util.Map.Entry;
import java.util.TreeMap;
public class TreeMapDemo {
public static void main(String[] a)
{
TreeMap<Integer, String> tm=new TreeMap<>();
tm.put(1, "RED");
tm.put(19, "BLUE");
tm.put(20, "BLACK");
tm.put(7, "ORANGE");
tm.put(20, "RED");
tm.put(31, "PURPLE");//sorted
for(Entry<Integer, String> e:tm.entrySet())
{
System.out.println(e.getKey()+"\t"+e.getValue());
}
}
}
Output:
1 RED
7 ORANGE
19 BLUE
20 RED
31 PURPLE
Another Example
import java.util.TreeMap;
class CustomKey implements Comparable<CustomKey>{
int a;
CustomKey(int a){this.a=a;}
@Override
public int compareTo(CustomKey o) {
return this.a-o.a;
}
}
public class TreeMapDemo {//TreeMap
Example
public static void main(String[] args) {
TreeMap<CustomKey, String> color=new TreeMap<>();
color.put(new CustomKey(2),"RED");
color.put(new CustomKey(51),"BLUE");
color.put(new CustomKey(19),"ORANGE");
color.put(new CustomKey(1),"PURPLE");
color.put(new CustomKey(36),"MAGENTA");
for(java.util.Map.Entry<CustomKey, String> s:color.entrySet())
{
System.out.println("Key:
"+s.getKey().a+"\t
value : "+s.getValue());
}
}
}Output:
Key: 1 value : PURPLE
Key: 2 value : RED
Key: 19 value : ORANGE
Key: 36 value : MAGENTA
Key: 51 value : BLUE
Methods
public boolean containsKey(Object key)
This method returns true if this map contains a mapping for
the defined key.
public void clear()
This method removes all of the mappings from this map. The
map will be empty after this call returns.
public boolean containsKey(Object key)
This method returns true if this map contains a mapping for
the defined key.
public boolean containsValue(Object value)
This method returns true if this map maps one or more keys
to the defined value. More formally, returns true if and only if this map
contains at least one mapping to a value v such that (value==null ? v==null :
value.equals(v)). This operation will probably require time linear in the map
size for most implementations.
public Set<Map.Entry<K,V>> entrySet()
This method returns a Set view of the mappings contained in
this map.
The set's iterator returns the entries in ascending key
order. The set's spliterator is late-binding, fail-fast, and additionally
reports Spliterator.SORTED and Spliterator.ORDERED with an encounter order that
is ascending key order.
public V get(Object key)
This method returns the value to which the defined key is
mapped, or null if this map contains no mapping for the key.
More formally, if this map contains a mapping from a key k
to a value v such that key compares equal to k according to the map's ordering,
then this method returns v; otherwise, it returns null.
This method returns a value of null does not necessarily indicate
that the map contains no mapping for the key; it's also possible that the map
explicitly maps the key to null. The containsKey operation may be used to distinguish
these two cases.
public V put(K key, V value)
public void putAll(Map<? extends K,? extends V> map)
This method copies all of the mappings from the defined map
to this map. These mappings replace any mappings that this map had for any of
the keys currently in the defined map.
