System,integer,calendar,random and Containers

System

1) arraycopy

Int[] A = {1.2.3.4};  Int[5]; System.arraycopy (a,1,b,3,2);  copies the element in array a from subscript 1 to the position labeled 3 in array B, copying 2 elements in total     

2) Currenttimemillis

Long L = system.currenttimemillis ();  returns the difference between the current time and January 01, 1970 0:0 0 seconds (ms)  

3) GC: Request system for garbage collection

4) public static string GetProperty (String key): Gets the value of the property name key property, key can take java.version,os.name,user.name,user.dir and so on.

Integer class

1) and int conversion (java1.5 and above)

int m = +//int to integerint n = in;  integer to int    

2) Parseint: Converts a numeric string to an int value

String s = "123";  int n = Integer.parseint (s);  convert s to int by 16, for example S "FF", then get 255    

3) Convert Tostring:int into a string to make a binary

int parseint (String s,int radix)

Caledar Class (Java.util)

1) Create Calendar class to hold the current time

Calendar C = calendar.getinstance ();

2) Use the Calendar class to represent a specified time

Public final void Set (int year,int month,int date)//month minus 1 for the actual month
Calendar C = calendar.getinstance (); C.set (2009,3-1,9);

3) public void set (int field,int value)--only sets the value of a field, Feild can take value calendar.year,calendar.day_of_week, etc.

4) public int get (int feild)--Gets the corresponding information in the Calendar object.

5) public abstract void Add (int feild, int amount)

Increase the date by 100 days

C.add (calendar.date, 100);

6) Public Boolean after (Object when): Determines whether the current date is behind the When, returns True, otherwise false

void Main (string[] args) {    // TODO auto-generated method stub Calendar c = calendar.getinstance (); C.s ET (3-1,9); Calendar C1 = calendar.getinstance (); C1.set (5-1,9Long t1 =long t2 = long days= (t1-t2)/(24*60*60 *1000); System.out.println (days);}         

Random class (java.util)

1) public Random (long Seed)

New Random (10);

2) The probability of public boolean nextboolean ()//50% generates true or False

3) public int nextint ()///Generate -231~231-1 number

Number between public int nextint (int n)//build [0,n)

4) The decimal between public double nextdouble ()//Generate [0,1.0]

List Series

Commonly used are ArrayList and LinkedList.

New ArrayList ();        List.add ("1"), List.add ("2"),List.add ("3"), List.add ("1"), List.add ("1"// inserting 1 where the index is 12, The elements behind the next move // index value of 2 are set to a////delete an element with an index value of 1        

Set series: No Repetition allowed

New HashSet ();        Set.add ("1"), Set.add ("2"), Set.add ("3"), Set.add ("1"), Set.add ("1"), Set.remove ("1");  Delete 1 Inside the collection, there is no 1 in the collection Iterator Iterator = set.iterator ();  while (Iterator.hasnext ()) {System.out.println (String) Iterator.next ());}       

The above code output 3,2

Map series (Take HashMap as an example)

hashmap<string,double> map =New hashmap<string,double>(); Note that you cannot use double map.put ("Apple", 0.5); // delete key for Orange for Map.Remove ("Orange" ); // modify Apple's corresponding value map.put ("Apple", 1.2); Set set = Map.keyset () Iterator Iterator = Set.iterator ( ); while (Iterator.hasnext ()) {String key = (String) Iterator.next (); double value = (double) map.get (key); SYSTEM.OUT.PRINTLN (key + "\ T" +       

System,integer,calendar,random and Containers