Java notes 10__math class, Random class, arrays class/Date action Class/object comparer/

/*** Math class, Random class, arrays class: Specific Java manual ... */ Public classMain { Public Static voidMain (string[] args) {string[] S1= {"A", "B", "C", "D", "E"}; string[] S2= {"A", "B", "C", "D", "E"}; Booleanb = Arrays.equals (S1,S2);//Compare two array contentsSystem.out.println (b);//Output Truestring[] S3=NewString[6]; Arrays.fill (S3,"Well Empty");        System.out.println (s3.length);  for(String i:s3) System.out.print (i+ "");                System.out.println (); String[] S4= Arrays.copyofrange (S1, 2, 3);//[2,3]         for(String i:s4) System.out.print (i+ "");                System.out.println (); intindex = Arrays.binarysearch (S1, "C");    SYSTEM.OUT.PRINTLN (index); }}

/*** Date Action class * Dates class: Represents a specific moment, accurate to milliseconds, and is the current time when the program is running * Calendar class: Can be accurate to milliseconds * DateFormat class * SimpleDateFormat class: Date formatting class*/ Public classMain { Public Static voidMain (string[] args) {Date D1=NewDate (); Date C=NewDate (); System.out.println (D1.gettime ()); //milliseconds indicatesSystem.out.println (D1);//Format Representation//two ways to instantiateCalendar CA1 =calendar.getinstance (); Calendar Ca2=NewGregorianCalendar ();//Solar Calendar        intYear =Ca1.get (calendar.year); intmonth = Ca1.get (calendar.month) +1; intDay =Ca1.get (Calendar.day_of_month); inthour =Ca1.get (Calendar.hour); intminute =Ca1.get (Calendar.minute); intSecond =Ca1.get (Calendar.second); System.out.println ( Year+ "" +month+ "" +Day ); System.out.println (Hour+ "" +minute+ "" +second); DateFormat DF1=dateformat.getdateinstance (); DateFormat DF2=dateformat.gettimeinstance (); String nowdate= Df1.format (NewDate ()); String Nowtime= Df2.format (NewDate ());        System.out.println (nowdate);                System.out.println (Nowtime); SimpleDateFormat SDF1=NewSimpleDateFormat ("Yyyy^mm^dd HH:mm:ss sss milliseconds"); String SWA= Sdf1.format (NewDate ());    SYSTEM.OUT.PRINTLN (SWA); }}

/*** Object comparer: Compare two or more data items to determine whether they are equal or determine the size relationship between them * Comparable interface: Forces the overall ordering of objects that implement each of its classes, and the CompareTo method of the class is called its natural comparison method * If the object of the custom class is to be sorted, then implement the comparable interface and implement the CompareTo method of the interface * * Comparable interface requires custom class to implement, according to OO principle: closed to the modification, open to the extension. * If this class is already defined and you don't want to change it, how do you do it? Answer: Arrays.sort has an overloaded method:*/ Public classMain { Public Static voidMain (string[] args) {string[] names= {"A", "B", "C", "D", "E", "F"}; person[] Persons= {            NewPerson ("a", 10),NewPerson ("B", 9),            NewPerson ("C", 8),NewPerson ("D", 7),            NewPerson ("E", 6),NewPerson ("F", 5),        }; //to sort an array of objects by a custom classarrays.sort (persons);  for(Person I:persons) System.out.println (i.name+ "" +i.age); Person2[] Persons2= {            NewPerson2 ("A", 10),NewPerson2 ("B", 9),            NewPerson2 ("C", 8),NewPerson2 ("D", 7),            NewPerson2 ("E", 6),NewPerson2 ("F", 5),        }; Arrays.sort (Persons2,NewPerson2comparator ());//using a custom comparer         for(Person2 i:persons2) System.out.println (i.name+ "" +i.age); System.out.println (arrays.tostring (PERSONS2));//returns a string representation of the contents of an array    }}classPersonImplementsComparable<person>{     PublicString name;  Public intAge ; Person (String name,intAge ) {         This. Name =name;  This. Age =Age ; } @Override Public intCompareTo (person O) {//Comparison method of comparators//implementation: Defining a comparison rule between objects        if(o==NULL){            Throw NewNullPointerException (); }        //returns 1 if the current object is less than the Parameter object//returns 0 if the current object equals a Parameter object//returns 1 if the current object is greater than the Parameter object        if( This. Age <o.age)return-1; Else if( This. Age <o.age)return1; return0; }}classperson2{ PublicString name;  Public intAge ; Person2 (String name,intAge ) {         This. Name =name;  This. Age =Age ; }}classPerson2comparatorImplementsComparator<person2>{@Override Public intCompare (Person2 O1, Person2 O2) {if(o1==NULL|| o2==NULL)           Throw NewNullPointerException (); if(O1.age <o2.age)return-1; Else if(O1.age >o2.age)return1; return0; }}

Java notes 10__math class, Random class, arrays class/Date action Class/object comparer/