It's a tribute. ~~java common code a basket hit

1. Get Environment variables


System.getenv ("PATH");


System.getenv ("Java_home");


2. Get System Properties


System.getproperty ("Pencil Color"); Get property value


Java-dpencil Color=green


System.getproperty ("Java.specification.version"); Get the Java version number


Properties p = system.getproperties (); Get all property values


P.list (System.out);


3.String Tokenizer


Ability to identify, and |


StringTokenizer st = new StringTokenizer ("Hello, world|of| Java ",", | ");


while (St.hasmoreelements ()) {


St.nexttoken ();


}


Treat the delimiter as token


StringTokenizer st = new StringTokenizer ("Hello, world|of| Java ",", | ", true);


4.StringBuffer (synchronous) and StringBuilder (non-synchronous)


StringBuilder sb = new StringBuilder ();


Sb.append ("Hello");


Sb.append ("World");


Sb.tostring ();


New StringBuffer (a). reverse (); Invert string


5. Digital


Convert between numbers and objects –integer to int


Integer.intvalue ();


Rounding of floating-point numbers


Math.Round ()


Digital formatting


NumberFormat


Integer---binary string


Tobinarystring () or valueof ()


Octal string, Integer


Tooctalstring ()


hexadecimal string, Integer


Tohexstring ()


Numbers formatted as Roman numerals


Romannumberformat ()


Random number


Random r = new Random ();


R.nextdouble ();


R.nextint ();


6. Date and time


View current date


Date today = new Date ();


Calendar.getinstance (). GetTime ();


Formatting the default zone date output


DateFormat df = dateformat.getinstance ();


Df.format (today);


Format to set the date output of the region


DateFormat DF_CN = dateformat.getdateinstance (Dateformat.full, Locale.china);


String now = Df_cn.format (today);


Print dates as required


SimpleDateFormat SDF = new SimpleDateFormat ("Yyyy-mm-dd hh:mm:ss");


Sdf.format (today);


Set a specific date


GregorianCalendar D1 = new GregorianCalendar (2009, 05, 06); June 6


GregorianCalendar D2 = new GregorianCalendar (); Today


Calendar d3 = Calendar.getinstance (); Today


D1.gettime (); Calendar or GregorianCalendar turns into date format


D3.set (Calendar.year, 1999);


D3.set (Calendar.month, Calendar.april);


D3.set (Calendar.day_of_month, 12);


String to date


SimpleDateFormat SDF = new SimpleDateFormat ("Yyyy-mm-dd hh:mm:ss");


Date now = Sdf.parse (String);


Date plus minus


Date now = new Date ();


Long T = Now.gettime ();


T + = 700*24*60*60*1000;


Date then = new Date (t);


Calendar now = Calendar.getinstance ();


Now.add (Calendar.year,-2);


Calculate date interval (converted to long to calculate)


Today.gettime () –old.gettime ();


Compare dates


Date type, use Equals (), before (), after () to calculate


Long type, use = =, <, > to calculate


Day of the Week


Use the Get () method of the calendar


Calendar C = calendar.getinstance ();


C.get (calendar.year);


Record time


Long start = System.currenttimemillis ();


Long end = System.currenttimemillis ();


long elapsed = End–start;


System.nanotime (); Milliseconds


Long shaping translates into seconds


Double.tostring (t/1000d);


7. Structured data


Array copy


System.arraycopy (Oldarray, 0, NewArray, 0, oldarray.length);


ArrayList


Add (Object O)//Adds the given element at the end


Add (int i, Object o)//Insert the given element at the specified position


Clear ()//Remove all elements from the collection


Contains (Object o)//If the vector contains a given element, returns the truth


Get (int i)//returns the object handle at the specified position


IndexOf (object o)//returns the index value of the given object if it is found; otherwise, 1


Remove (object o)//delete object by reference


Remove (int i)//delete objects by location


ToArray ()//Returns an array containing the collection object


Iterator


List List = new ArrayList ();


Iterator it = List.iterator ();


while (It.hasnext ())


Object o = It.next ();


Linked list


LinkedList list = new LinkedList ();


Listiterator it = List.listiterator ();


while (It.hasnext ())


Object o = It.next ();


HashMap


Hashmap<string, string> HM = new hashmap<string, string> ();


Hm.get (key); Get Value by key


Hm.put ("No1", "Hexinyu");


Hm.put ("No2", "Sean");


Method 1: Get all key values


Iterator<string> it = hm.values (). Iterator ();


while (It.hasnext ()) {


String MyKey = It.next ();


String myvalue = Hm.get (MyKey);


}


Method 2: Get all key values


For (String Key:hm.keySet ()) {


String MyKey = key;


String myvalue = Hm.get (MyKey);


}


preferences– system-related user settings, similar to name-value pairs


Preferences prefs = Preferences.usernodeforpackage (Arraydemo.class);


String Text = Prefs.get ("Textfontname", "lucida-bright");


String display = Prefs.get ("Displayfontname", "Lucida-balckletter");


System.out.println (text);


SYSTEM.OUT.PRINTLN (display);


The user sets the new value and stores it back


Prefs.put ("Textfontname", "new-bright");


Prefs.put ("Displayfontname", "New-balckletter");


properties– similar to the name-value pair, between key and value, can be separated by "=", ":" or a Space, with "#" and "!" Comments


InputStream in = MediationServer.class.getClassLoader (). getResourceAsStream ("msconfig.properties");


Properties prop = new properties ();


Prop.load (in);


In.close ();


Prop.setproperty (key, value);


Prop.getproperty (key);


Sort


1. Array: Arrays.sort (strings);


2. List:Collections.sort (List);


3. Custom class: Class Subcomp implements Comparator


Then use Arrays.sort (strings, New Subcomp ())


Two interfaces


1. Java.lang.Comparable: Provides a natural ordering of objects, built into classes


int CompareTo (Object o);


Boolean equals (Object O2);


2. Java.util.Comparator: Provide a specific comparison method


int compare (object O1, Object O2)


Avoid repeating sorting, you can use TreeMap


TreeMap sorted = new TreeMap (UNSORTEDHASHMAP);


Exclude duplicate elements


Hashset hs–new Hashset ();


Search for objects


BinarySearch (): Quick query –arrays, collections


Contains (): Line Search –arraylist, HashSet, Hashtable, LinkedList, Properties, Vector


ContainsKey (): Checks whether the collection object contains a given –hashmap, Hashtable, Properties, TreeMap


Containsvalue (): Primary key (or given value) –hashmap, Hashtable, Properties, TreeMap


IndexOf (): If a given object is found, return its position –arraylist, LinkedList, List, Stack, Vector


Search (): Linear search –stack


Set-to-go array


ToArray ();


Collection Summary


Collection:set–hashset, TreeSet


Collection:list–arraylist, Vector, LinkedList


Map:hashmap, HashTable, TreeMap


8. Generics and foreach


Generic type


list<string> myList = new arraylist<string> ();


Foreach


for (String s:mylist) {


System.out.println (s);


}


9. Object-Oriented


ToString () formatting


public class Tostringwith {


int x, y;


Public Tostringwith (int anX, int aY) {


x = AnX;


y = AY;


}


Public String toString () {


Return "tostringwith[" + x + "," + y + "]";


}


public static void Main (string[] args) {


System.out.println (New Tostringwith (43, 78));


}


}


Overriding the Equals method


public boolean equals (Object o) {


if (o = = this)//optimize


return true;


if (! ( o instanceof Equalsdemo)//Can be projected into this class


return false;


Equalsdemo other = (Equalsdemo) o; Type conversions


if (int1! = other.int1)//By field comparison


return false;


if (!obj1.equals (OTHER.OBJ1))


return false;


return true;


}


Overriding the Hashcode method


private volatile int hashcode = 0; Deferred initialization


public int hashcode () {


if (hashcode = = 0) {


int result = 17;


result = PNS * result + AreaCode;


}


return hashcode;


}


Clone method


To clone an object, you must first do two steps: 1. The Clone () method of the overlay object; 2. Implement an empty Cloneable interface


public class Clone1 implements cloneable {


Public Object Clone () {


return Super.clone ();


}


}


Finalize method


Object F = new Object () {


public void Finalize () {


System.out.println ("Running Finalize ()");


}


};


Runtime.getruntime (). Addshutdownhook (New Thread () {


public void Run () {


System.out.println ("Running Shutdown Hook");


}


});


The two methods will be executed when calling System.exit (0);


Singleton mode


Implementation 1


public class Mysingleton () {


public static final Mysingleton INSTANCE = new Mysingleton ();


Private Mysingleton () {}


}


Implementation 2


public class Mysingleton () {


public static Mysingleton instance = new Mysingleton ();


Private Mysingleton () {}


public static Mysingleton getinstance () {


return instance;


}


}


Custom exceptions


Exception: Compile-time check


RuntimeException: Run-time check


public class MyException extends RuntimeException {


Public MyException () {


Super ();


}


Public myexception (String msg) {


Super (MSG);


}


}


10. Input and output


Stream, Reader, Writer


Stream: Processing byte stream


Reader/writer: Handling characters, Universal Unicode


Reading data from a standard input device


1. Read bytes with System.in's Bufferedinputstream ()


int b = System.in.read ();


System.out.println ("Read Data:" + (char) b); Cast to character


2. BufferedReader reading text


If you are transferring from stream to reader, use the InputStreamReader class


BufferedReader is = new BufferedReader (new


InputStreamReader (system.in));


String Inputline;


while ((Inputline = Is.readline ()) = null) {


System.out.println (Inputline);


int val = integer.parseint (inputline); If Inputline is an integer


}


Is.close ();


Write data to standard output devices


1. Print data using System.out's println ()


2. Print with PrintWriter


PrintWriter pw = new PrintWriter (System.out);


Pw.println ("The answer is" + Myanswer + "at this time.");


Formatter class


Format the content of the print


Formatter fmtr = new Formatter ();


Fmtr.format ("%1$04d–the Year of%2$f", 1951, Math.PI);


or System.out.printf (); or System.out.format ();


Original scan


void Dofile (Reader is) {


int C;


while ((c = Is.read ())! =-1) {


System.out.println ((char) c);


}


}


Scanner Scan


Scanner can read file, InputStream, String, readable


try {


Scanner scan = new Scanner (New File ("A.txt"));


while (Scan.hasnext ()) {


String s = scan.next ();


}


} catch (FileNotFoundException e) {


E.printstacktrace ();


}


}


Read file


BufferedReader is = new BufferedReader (New FileReader ("MyFile.txt"));


Bufferedoutputstream BOS = new Bufferedoutputstream (New FileOutputStream ("Bytes.bat"));


Is.close ();


Bos.close ();


Copying files


Bufferediutputstream is = new Bufferediutputstream (New Fileiutputstream ("OldFile.txt"));


Bufferedoutputstream OS = new Bufferedoutputstream (New FileOutputStream ("NewFile.txt"));


int b;


while ((b = Is.read ())! =-1) {


Os.write (b);


}


Is.close ();


Os.close ();


File read-in string


StringBuffer sb = new StringBuffer ();


Char[] B = new char[8192];


int n;


Read a block, if there are characters, add buffer


while ((n = is.read (b)) > 0) {


Sb.append (b, 0, N);


}


return sb.tostring ();


REDIRECT Standard stream


String logfile = "Error.log";


System.seterr (New PrintStream (New FileOutputStream (logfile)));


Read and write different character set literals


BufferedReader Chinese = new BufferedReader (new InputStreamReader (New FileInputStream ("Chinese.txt"), "iso8859_1"));


PrintWriter standard = new PrintWriter (new OutputStreamWriter (New FileOutputStream ("Standard.txt"), "UTF-8");


Read binary data


DataOutputStream OS = new DataOutputStream (New FileOutputStream ("A.txt"));


Os.writeint (i);


Os.writedouble (d);


Os.close ();


Read data from a specified location


Randomaccessfile RAF = new Randomaccessfile (FileName, "R"); R indicates read-only open


Raf.seek (15); Read starting from 15


Raf.readint ();


Raf.radline ();


Serialization objects


Object serialization, the serializable interface must be implemented


Save data to disk


ObjectOutputStream OS = new ObjectOutputStream (new Bufferedoutputstream (New FileOutputStream (FILENAME));


Os.writeobject (Serialobject);


Os.close ();


Read the data


ObjectInputStream is = new ObjectInputStream (new FileInputStream (FILENAME));


Is.readobject ();


Is.close ();


Read or write a jar or zip document


ZipFile zippy = new ZipFile ("A.jar");


Enumeration all = Zippy.entries (); Enumeration values list all file lists


while (All.hasmoreelements ()) {


ZipEntry entry = (zipentry) all.nextelement ();


if (Entry.isfile ())


println ("Directory:" + entry.getname ());


Read and write files


FileOutputStream OS = new FileOutputStream (Entry.getname ());


InputStream is = Zippy.getinputstream (entry);


int n = 0;


Byte[] B = new byte[8092];


while ((n = is.read (b)) > 0) {


Os.write (b, 0, N);


Is.close ();


Os.close ();


}


}


Read and write gzip documentation


FileInputStream fin = new FileInputStream (FILENAME);


Gzipinputstream Gzis = new Gzipinputstream (FIN);


InputStreamReader xover = new InputStreamReader (Gzis);


BufferedReader is = new BufferedReader (xover);


String Line;


while (line = Is.readline ()) = null)


System.out.println ("Read:" + line);

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It's a tribute. ~~java common code a basket hit