Comparable interface, map interface, generic

Comparable Interface

Class that implements the comparable interface. objects can be compared between different sizes.
The comparable interface has only one method.
Public int compareto (Object OBJ );
This method: returns 0 indicating this = OBJ
Returns a positive value indicating this> obj.
Returns a negative number, which indicates this> obj.
The class implementing the comparable interface uses the compareto method to determine the object sorting method.
You can use the sort () method to sort data.

Data structure selection:
Measurement criteria: Read efficiency and change Efficiency
Slow array read/write speed
Linked changed to fast-read and slow
Hash

 

Map Interface

The class that implements the map interface is used to store key-value pairs.
Implementation classes of the map interface include hashmap and treemap.
Key-value pairs stored in the map class are identified by keys. Therefore, key-value pairs cannot be repeated.
Object put (Object key, object value); // if the key already exists, the value of the original key is returned.
Object get (Object key );
Object remove (Object key );
Boolean containskey (Object key );
Boolean containsvalue (object value );
Int size ();
Boolean isempty ();
Void putall (MAP t );
Void clear ();
Use the hashcode () method for comparison.

 

Generic:

Enhance program readability and Stability
Define the object type in the collection at the same time when defining the set
Example:
Import java. util .*;
Public class testargswords {
Private Static final int one = 1;
Public static void main (string [] ARGs ){
Map <string, integer> M = new hashmap <string, integer> (); // generic
For (INT I = 0; I <args. length; I ++ ){
Int freq = (integer) M. Get (ARGs [I]) = NULL? 0 :( integer) M. Get (ARGs [I]);
M. Put (ARGs [I], freq + 1 );
}
System. Out. println (M. Size () + "distinct words detected :");
System. Out. println (m );
}
}
You can specify
You can also use iterator to specify