Container knowledge summary:
1. Collection interface _
Common methods in the Collection interface:
Size()
isEmpty()
clear()
contains()
add()
remove()
iterator() : returns its pointer
2. List ( ArrayList & LinkedList ) : Inherited from Collection , adding the following common methods:
get(int index)
set(int index,Object element) : set the value, different from add
indexof(Object o) : returns the index
3. Set ( HashSet & TreeSet ) : inherited from Collection , no additional methods are added;
4. Map ( HashMap & TreeMap ) : Commonly used methods are as follows:
put(Object key,Object value)
get(Object key)
remove(Object key)
boolean containsKey(Object key)
boolean containsValue(Object value)
int size()
Boolean isEmpty()
clear()
5. Collections class : provides some static methods to implement some common algorithms based on List container :
void sort(List) : sort
void reverse(List) : reverse
void shuffle(List) : random sorting
void fill(List,Object) : rewrite List with specific object
void copy(List desc,List src) : copy src to desc
int binarySearch(List, Object) : For a sequential List container, use the half-search method to find a specific object
6. Iterator interface : Each Collection interface and its sub-interfaces have an iterator () method that returns a pointer to its object. The pointer starts at the left of the first element. This interface has only three methods:
Boolean hasNext() : Whether there is an element to the right of the pointer
E next() : returns the element to the right of the pointer
Void remove() : delete the element to the left of the pointer, this operation can only be performed once after executing next
7. Comparable interface : To compare the sizes of containers , the Comparable interface is often inherited , and its comparaTo method is rewritten to define the comparison rules:
Java.lang.Comparable (note the interface under the java.lang package)
public int compareTo(Object obj)：
Return 0 : means: this = obj
Returns a positive number: means: this > obj
Returns a negative number: means: this < obj
8. The difference between Collection and Collections :
Collection is the parent interface of list and set , and Collections only provides some common tool methods for List interface
In general, just remember a diagram:
Set : no order, not repeatable
List : in order, repeatable
Map : store key-value test tests