Java Collection -001 Collection

Have not come to do a good job of the Java collection of commonly used classes, because the interview asked the collection of more in-depth not how to answer well, now come good likes and dislikes to fill.

Java collection classes are primarily derived from 2 interfaces: Collection, Map

The following figure is a set of collection tree, mainly derived from set, List, Queue three major categories

The following figure is a map-derived collection system tree

in this section we only discuss the methods of the collection interface

Add (Object O): This method is used to add an element

AddAll (Collection C): This method adds all the elements in the set C to the specified set

Clear (): clearly set all elements inside the collection

Contains (Object O): Returns whether the collection contains the specified element o

Containsall (Collection C): Returns whether the collection contains all the elements within the specified set C

IsEmpty (): Returns whether the collection is an empty collection

Iterator (): Returns a Iterator object user traversal collection

Remove (Object o): Deletes the specified element o

RemoveAll (collectoin c): Delete all the elements contained within the set C

Size (): Returns the number of elements in a collection

ToArray (): Converting a collection to an array

These methods are commonly used in our approach.

Traversal collection collection mainly useful iterator, for these 2 kinds of

Collection C = new ArrayList ();

C.add ("1");

C.add ("2");

Using iterator to traverse the collection C

Iterator it = C.iterator ();

while (It.hasnext ()) {

System.out.println (It.next ());

}

Using foreach to traverse the collection C

for (Object o:c) {

System.out.println (o);

}

Collection interface is introduced here will be a detailed introduction to set, list, map several commonly used interfaces.