Package COM. yang. ex18; import Java. util. properties;/** system: the methods and properties in the class are static. * Out: standard output. The default value is console * In: standard input, by default, the keyboard ** describes system information * obtains system property information: Properties getproperties () **/public class demo {public static void main (string [] ARGs) {// todo auto-generated method stub properties = system. getproperties (); // because properties is a subclass of hashtable, it is also a subclass object of the map set. // You can use the map method to retrieve the elements in the set. All the elements stored in the set are strings without generic definitions. // you can customize some special information system in the system. setproperty ("key", "value"); // gets the specified property information system. getproperty ("OS. name "," value "); // when JVM is started, some attribute information is dynamically loaded string v = system. getproperty ("hah1"); system. out. println (V); For (Object object: properties. keyset () {string value = (string) properties. get (object); system. out. println (value) ;}} package COM. yang. ex18; import Java. text. simpledatef Ormat; import Java. util. *; public class datedemo {public static void main (string ARGs []) {date = new date (); system. out. println (date); simpledateformat sdateformat = new simpledateformat ("mm DD, yyyy hh: mm e "); // call the format method to format the specified date object string tistring = sdateformat. format (date); system. out. println (tistring) ;}} package COM. yang. ex18; import Java. text. simpledateformat; import Java. util. calendar; impor T Java. util. date; public class calendardemo {public static void main (string [] ARGs) {// todo auto-generated method stub date = new date (); Calendar calendar = calendar. getinstance (); system. out. println (calendar); system. out. println (calendar. get (calendar. year); system. out. println (calendar. get (calendar. month); system. out. println (); // simpledateformat = new simpledateformat ("yyy Y "); // string yearstring = simpledateformat. format (date); // system. out. println (yearstring); // }}} package COM. yang. ex18; import Java. util. random; public class mathdemo {public static void main (string [] ARGs) {// todo auto-generated method stub double D = math. ceil (12.34); // Ceil returns the smallest integer system greater than the specified data. out. println (d); long l = math. round (12.24); // round to random r = new random (); system. out. println (l); For (int I = 0; I <10; I ++) {double d1 = (INT) (math. random () * 10 + 1); int D2 = R. nextint (10); system. out. println (D2) ;}} package COM. yang. ex18;/** runtime object: * The constructor is not provided in this class. It indicates that the new object is not allowed. * You will directly think that the methods in this class are static. * You will find that there are non-static methods in this class. * This class will certainly provide methods to obtain the class objects, the method is static, and the returned value * type is the class type. ** This method is: static runtime getruntime (); * This feature shows that this class uses the single-column design mode to complete **/public class runtimedemo {public static void main (string [] ARGs) throws exception {// todo auto-generated method stubruntime runtime = runtime. getruntime (); process process=runtime.exe C ("notepad.exe demo. java "); // process. destroy ();}}
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Dark Horse programmer-common objects
