【每天学一点】JAVASE01 (1)

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　　昨天程序写的比较晚，所以没来得及更新，今天补上。真是每天都是一个新的开始。主要是，似乎还是得找WEB方向的，所以一般都是招JAVA开发，对于一个0基础的我，从头学的话还是有点要花时间，不过昨天看了看SE好在和C++差不多，计划是先学SE然后开始转EE什么的。总之，因为学了很多语言的基础，再学一门新的语言，基础的话应该能够很快上手吧，大概！
　　

一些基本数据结构

////-----------------数组排序-----------    public static void main(String[] args) {        int[] a=new int[]{1,4,2,1,6,435,132,-23};        int[] b={1,3,4,2,32,56,8};        Arrays.sort(a);    //快速排序方法        for(int i:a)        System.out.println(i);    }////-----------数组初始化------------------    public static void main(String[] args) {        int[] arr2=new int[]{1,2,3,4,5,6};    //第一种        int[] arr1={1,2,3,4,5};    //第二种////----------------数组引用-------------------        int[] arr=arr1;  //arr相当于arr1的引用，即别名                    arr[1]=10;   //此时arr1[1]=10//---------------------数组拷贝值-----------        int[] copyArr=Arrays.copyOf(arr1, arr1.length);        copyArr[1]=11;     //只有copyArr[1]的值被改变        for(int i:arr)            System.out.print(i+" ");        System.out.println("");        for(int i:arr1)            System.out.print(i+" ");        System.out.println("");        for(int i:arr2)            System.out.print(i+" ");        System.out.println("");        for(int i:copyArr)            System.out.print(i+" ");////------------------大数值-------------    public static void main(String[] args) {        BigInteger a=BigInteger.valueOf(100);  //将100转换为大数值        BigInteger b=a.add(a);     //b=a+20        BigInteger c=a.subtract(b); //c=a-2        BigInteger d=a.multiply(c);  //d=a*c        BigInteger e=a.divide(d);  //e=a/d        int f=a.compareTo(e);   //= 0;> + ;< -        System.out.println(a+" "+b+" "+c+" "+d+" "+e+" "+f);//  }////-----------file process------------    public static void main(String[] args) throws IOException{         Scanner in=new Scanner(Paths.get("E:\\java\\workspace\\helloworld\\bin\\a.txt"));        String name=in.nextLine();        System.out.println(name);        PrintWriter out=new PrintWriter("E:\\java\\workspace\\helloworld\\bin\\a.txt");    }////---------------读取账号密码-Console---------- ???????????    public static void main(String[] args) {    Console cons=System.console();    String name=cons.readLine("user name: ");    Scanner in=new Scanner(System.in);    name=in.nextLine();    char[] passwd=cons.readPassword("password: ");    }//  //---------------cin,cout-----------------    public static void main(String[] args) {        Scanner in=new Scanner(System.in);  //构造一个Scanner对象，并与System.in关联        System.out.println("what is your name?");        String name=in.nextLine();      //输入一行        System.out.println("what is your sex");        String sex=in.next();    //输入一个单词以空格为分隔符        System.out.println("How old are you");        int age=in.nextInt();   //输入一个整数        System.out.println("name: "+name+"; sex: "+sex+" age: "+age);        in.close();    }//  //----------java.lang.StringBuilder--------    public static void main(String[] args) {    StringBuilder z=new StringBuilder();    String str="i m ";     z.append(str);    z.append("reimu ");    z.insert(2,"a");      String s=z.toString();    System.out.println(s);   //output i am reimu    //if z refers to a string builder object whose    //current contents are "start", then the method call z.append("le")    //would cause the string builder to contain "startle",     //whereas z.insert(4, "le") would alter the string builder    //to contain "starlet".    z.delete(5,11);  //delete index: 5-10    System.out.println(z);  //output i am .    }//-------other java.lang.string-----------------    public static void main(String[] args) {        String s=" hello,world! ";        s=s.toUpperCase();  //upper        System.out.println(s);        s=s.toLowerCase();  //lower        System.out.println(s);        s=s.trim();        System.out.println(s); //delete head and end spaces     }//-------------code units and code point-----       public static void main(String[] args) {        String s="hello";        System.out.println(s.length());  //s.length        int count=s.codePointCount(0,s.length());//实际字符数        System.out.println(count);    //output 5        int cPA=s.codePointAt(0);  //返回ascii码        System.out.println(cPA);         char first=s.charAt(0);          char last=s.charAt(s.length()-1);        System.out.println(first+" "+last);    }////------------empty string:length=0;---------    public static void main(String[] args) {        String str="";   //no spaces        //str=null;  if str=null,cannot use function        if(str.length()==0||str.equals("")){            System.out.println("empty string");        }        else            System.out.println("it isn't a empty string");    }////-------------equals------yes->true;no->false------////-----------equalsIgnoreCase-----------    public static void main(String[] args) {        String s1="hello";        String s2="HELLO";        if(s1.equalsIgnoreCase(s2)){            if(s1.equals(s2))                System.out.println("s1=s2");            else                System.out.println("ignorecase,s1=s2");        }        else            System.out.println("s1!=s2");    }    //output:ignorecase,s1=s2////---------------substring---from a father string to getting a son string--    public static void main(String[] args) {        String s="i am lyy!";        String s1=s.substring(2);   //cut 0-1,at 2 start        System.out.println(s1);     //output :am lyy!        String s2=s.substring(2, 4);        System.out.println(s2);     //output :am. string length:4-2=2        s2="i am";        System.out.println(s2);    }////------------type cast---------------    public static void main(String[] args) {        double x=9.9;        int y=(int)x;        System.out.println(y);  //output 9,get close x's min int    }////------Math function--------------------    public static void main(String[] args) {        double[] x=new double[6];        double y=4;        x[0]=Math.sqrt(y);        x[1]=Math.sin(y);        x[2]=Math.PI;        x[3]=Math.E;        x[4]=Math.pow(y,2);        x[5]=Math.exp(y);        for(double i:x)        System.out.println(i);    }////------------variable---final----------------    public static void main(String[] args) {                int val=10;        final int con=12;  //it's not similar to c++,using 'final' to define a constant        val=11;        System.out.println(val+con);    }    public static void main(String[] args){        System.out.print("helloworld");        for(int i=0;i<10;i++){            System.out.print(i);        }    }////-----------hello world--------------------------------    public stat```````c void main(String[] args) {        String[] hello=new String[3];        hello[0]="hello ";        hello[1]="i am ";        hello[2]="lyy.";        for(String i:hello){            System.out.println(i);  //自动换行            System.out.print(i);  //不自动换行        }

类，继承：

//----------------------抽象类Person----------------------------abstract public class Person {    private String Name;    public Person(String name){        Name=name;    }    public abstract String getDescription();   //抽象方法，不在这儿定义，但子类需要定义    public String getName() {        return Name;    }   }//-------------------------学生类Student继承Person----------------------public class Student extends Person{    private String Major;    public Student(String name,String major){        super(name);    //对person进行初始化        Major=major;            }    public String getDescription(){        return "i am a student,my name is: "+super.getName()+",major is: "+Major;    }    public String getMajor() {        return Major;    }    public void setMajor(String major) {        Major = major;    }}//-----------------------员工类Employee继承Person------------------------import java.util.Date;import java.util.GregorianCalendar;public class Employee extends Person{    private int Age;    private double Salary;    private Date Hireday;    private static int NextId=1;  //属于类，不属于对象。任何一个对象都有NextId=1,即使对象不存在NextID也存在    private int Id;    public Employee(String name,int age ,double salary,int year,int month,int day){        super(name);        this.Age=age;        this.Salary=salary;        GregorianCalendar cal=new GregorianCalendar(year,month-1,day); //0表示1月        this.Hireday=cal.getTime();         }    public Employee(String name){        super(name);    }    public Employee(){        super("");        this.Age=0;        this.Salary=0;        this.Hireday=new Date();    }    //初始化块，在构造器初始化前自动运行    {        this.Id=NextId;        NextId++;    }    public String getDescription(){        return "i am a employee,my name is: "+super.getName();    }    public void raiseSalary(double byPercent){        double raise=Salary*byPercent/100;        this.Salary+=raise;    }    public int getId(){        return Id;    }    public void setId(){        this.Id=NextId;        NextId++;    }    public int getAge() {        return Age;    }    public void setAge(int age) {        Age = age;    }    public double getSalary() {        return Salary;    }    public void setSalary(double salary) {        Salary = salary;    }    public String getName() {        return super.getName();    }    public Date getHireday() {        return  (Date) Hireday.clone();    }    public void setHireday(Date hireday) {        Hireday = hireday;    }}//----------------------经理类Manage继承Employee----------------------import java.util.GregorianCalendar;final public class Manage extends Employee{   //不允许其他类继承Manage    private static int BossId=1;    private double Bounds;    private int Bid;    public Manage(String name,int age ,double salary,int year,int month,int day,double bounds){        super(name);        super.setAge(age);        this.setSalary(salary);        GregorianCalendar cal=new GregorianCalendar(year,month-1,day);        this.setHireday(cal.getTime());        this.Bounds=bounds;    }    {        Bid=BossId;        BossId++;    }    public double getBounds() {        return Bounds;    }    public void setBounds(double bounds) {        Bounds = bounds;    }    public String getName(){        return super.getName();    }    public int getBid() {        return Bid;    }    public void setBid(int bid) {        Bid = bid;    }}//-------------------main-----------------import java.util.Date;public class Helloworld {    public static void main(String[] args) {        Employee[] staff=new Employee[4];        staff[0]=new Employee("alex", 18, 2000, 2016, 2, 3);        staff[1]=new Employee("Bob", 19, 2500, 2016, 3, 2);        staff[2]=new Employee("Carl", 20, 3000, 2016, 5, 3);        staff[3]=new Employee();        for(Employee i:staff){            //i.setId();            i.raiseSalary(5);            }        for(Employee e:staff)            System.out.println("id="+e.getId()+",name= "+e.getName()+",age="+e.getAge()+",salary="+e.getSalary()+                    ",hireday="+e.getHireday());        Date d=staff[0].getHireday();                     //若返回的是一个可变对象的引用，则容易改变封装性，一般需要加.clone()        d.setTime(d.getTime()-(long)365*24*60*60*1000);           System.out.println(staff[0].getHireday());        Manage boss=new Manage("Boss", 18, 6000, 2014, 5, 3, 500);        System.out.println("bid="+boss.getBid()+",name="+boss.getName()+",age="+boss.getAge()+                ",salary="+boss.getSalary()+",bounds="+boss.getBounds()+",hireday="+boss.getHireday());        Person p1,p2;        p1=new Student("xxm", "math");        System.out.println(p1.getDescription());        p2=new Employee("gws", 19, 2000, 2016, 5, 5);        p2.getDescription();        Manage m=new Manage("ssss", 54, 15, 2015, 2, 2, 500);        System.out.println(m.getName()+" "+m.getBounds());        Employee e=new Manage("ssdq", 445, 12, 2012, 12, 12, 500);        System.out.println(e.getName()+" "+e.getDescription());    }

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