201771010135杨蓉庆《面向对象程序设计（java）》第四周学习总结(代码片段)

学习目标

import java.io.*;
import java.util.*;
public class FileWriteReadTest 
    public static void main(String[] args) throws IOException
        //写入文件演示
        PrintWriter out = new PrintWriter("myfile.txt");
        out.println("姓名 高数 Java 数据结构 平均成绩 总成绩");
        out.println("张三 20 30 40 0 0");
        out.println("李四 50 60 70 0 0");
        out.close();//输出完毕，需要close
        //读入文件演示
        Scanner in = new Scanner(new File("myfile.txt"));//为myfile.txt这个File创建一个扫描器in
        int number = 1;//行号
        System.out.println(in.nextLine());
        while(in.hasNextLine())//判断扫描器是否还有下一行未读取，该循环把文件的每一行都读出
            String line = in.nextLine();//读出myfile.txt的下一行
            System.out.print("第"+(++number)+"行的内容: ");            
            Scanner linescanner = new Scanner(line);//行内容建立扫描器
            linescanner.useDelimiter(" ");//使用空格作为分隔符
            String name = linescanner.next();
            String math = linescanner.next();
            String java = linescanner.next();
            String ds = linescanner.next();
            String avg = linescanner.next();
            String total = linescanner.next();
            System.out.println("name="+name+"  math="+math+"  java="+java+"  ds="+ds+"  avg"+avg+"  total="+total);
        
        in.close();//读入完毕，最后需要对其进行close。
        

import java.util.Scanner;
    public class StudentTest
    
       @SuppressWarnings("resource")
    public static void main(String[] args)
       
          Student[] staff = new Student[3];
          System.out.println("请输入学生的信息");
         
          Scanner in = new Scanner(System.in); 
          for(int i=0;i<staff.length;i++) 
              staff[i]=new Student(in.next(),in.next(),in.nextInt());
          
          System.out.println("name"+" "+"sex"+" "+"javascore");

          for (Student e : staff)
             System.out.println(e.getName() +"    "+e.getSex()+"          "+e.getJavaScore());
       
    

    class Student
    
       private String name;
       private String sex;
       private int javascore;

       public Student(String n, String s, int j)
       
          name = n;
          sex = s;
          javascore =j;
       

       public String getName()
       
          return name;
       

       public String getSex()
       
          return sex;
       

       public int getJavaScore()
       
          return javascore;
       
    
    
    

/**
 * This program demonstrates static methods.
 * @version 1.01 2004-02-19
 * @author Cay Horstmann
 */
public class StaticTest

   public static void main(String[] args)
   
      // fill the staff array with three Employee objects
      Employee[] staff = new Employee[3];

      staff[0] = new Employee("Tom", 40000);
      staff[1] = new Employee("Dick", 60000);
      staff[2] = new Employee("Harry", 65000);

      // print out information about all Employee objects
      for (Employee e : staff)
      
         e.setId();
         System.out.println("name=" + e.getName() + ",id=" + e.getId() + ",salary="
               + e.getSalary());
      

      int n = Employee.getNextId(); // calls static method
      System.out.println("Next available id=" + n);
   


class Employee

   private static int nextId = 1;

   private String name;
   private double salary;
   private int id;

   public Employee(String n, double s)
   
      name = n;
      salary = s;
      id = 0;
   

   public String getName()
   
      return name;
   

   public double getSalary()
   
      return salary;
   

   public int getId()
   
      return id;
   

   public void setId()
   
      id = nextId; // set id to next available id
      nextId++;
   

   public static int getNextId()
   
      return nextId; // returns static field
   

   public static void main(String[] args) // unit test
   
      Employee e = new Employee("Harry", 50000);
      System.out.println(e.getName() + " " + e.getSalary());
   

/**
 * This program demonstrates parameter passing in Java.
 * @version 1.00 2000-01-27
 * @author Cay Horstmann
 */
public class ParamTest

   public static void main(String[] args)
   
      /*
       * Test 1: Methods can‘t modify numeric parameters
       */
      System.out.println("Testing tripleValue:");
      double percent = 10;
      System.out.println("Before: percent=" + percent);
      tripleValue(percent);
      System.out.println("After: percent=" + percent);

      /*
       * Test 2: Methods can change the state of object parameters
       */
      System.out.println("
Testing tripleSalary:");
      Employee harry = new Employee("Harry", 50000);
      System.out.println("Before: salary=" + harry.getSalary());
      tripleSalary(harry);
      System.out.println("After: salary=" + harry.getSalary());

      /*
       * Test 3: Methods can‘t attach new objects to object parameters
       */
      System.out.println("
Testing swap:");
      Employee a = new Employee("Alice", 70000);
      Employee b = new Employee("Bob", 60000);
      System.out.println("Before: a=" + a.getName());
      System.out.println("Before: b=" + b.getName());
      swap(a, b);
      System.out.println("After: a=" + a.getName());
      System.out.println("After: b=" + b.getName());
   

   public static void tripleValue(double x) // doesn‘t work
   
      x = 3 * x;
      System.out.println("End of method: x=" + x);
   

   public static void tripleSalary(Employee x) // works
   
      x.raiseSalary(200);
      System.out.println("End of method: salary=" + x.getSalary());
   

   public static void swap(Employee x, Employee y)
   
      Employee temp = x;
      x = y;
      y = temp;
      System.out.println("End of method: x=" + x.getName());
      System.out.println("End of method: y=" + y.getName());
   


class Employee // simplified Employee class

   private String name;
   private double salary;

   public Employee(String n, double s)
   
      name = n;
      salary = s;
   

   public String getName()
   
      return name;
   

   public double getSalary()
   
      return salary;
   

   public void raiseSalary(double byPercent)
   
      double raise = salary * byPercent / 100;
      salary += raise;
   

import java.util.*;

/**
 * This program demonstrates object construction.
 * @version 1.01 2004-02-19
 * @author Cay Horstmann
 */
public class ConstructorTest

   public static void main(String[] args)
   
      // fill the staff array with three Employee objects
      Employee[] staff = new Employee[3];

      staff[0] = new Employee("Harry", 40000);
      staff[1] = new Employee(60000);
      staff[2] = new Employee();

      // print out information about all Employee objects
      for (Employee e : staff)
         System.out.println("name=" + e.getName() + ",id=" + e.getId() + ",salary="
               + e.getSalary());
   


class Employee

   private static int nextId;

   private int id;
   private String name = ""; // instance field initialization
   private double salary;
  
   // static initialization block
   static
   
      Random generator = new Random();
      // set nextId to a random number between 0 and 9999
      nextId = generator.nextInt(10000);
   

   // object initialization block
   
      id = nextId;
      nextId++;
   

   // three overloaded constructors
   public Employee(String n, double s)
   
      name = n;
      salary = s;
   

   public Employee(double s)
   
      // calls the Employee(String, double) constructor
      this("Employee #" + nextId, s);
   

   // the default constructor
   public Employee()
   
      // name initialized to ""--see above
      // salary not explicitly set--initialized to 0
      // id initialized in initialization block
   

   public String getName()
   
      return name;
   

   public double getSalary()
   
      return salary;
   

   public int getId()
   
      return id;
   

import com.horstmann.corejava.*;
// the Employee class is defined in that package

import static java.lang.System.*;

/**
 * This program demonstrates the use of packages.
 * @version 1.11 2004-02-19
 * @author Cay Horstmann
 */
public class PackageTest

   public static void main(String[] args)
   
      // because of the import statement, we don‘t have to use 
      // com.horstmann.corejava.Employee here
      Employee harry = new Employee("Harry Hacker", 50000, 1989, 10, 1);

      harry.raiseSalary(5);

      // because of the static import statement, we don‘t have to use System.out here
      out.println("name=" + harry.getName() + ",salary=" + harry.getSalary());
   

import java.util.Scanner;
public class Rectangle // 创建一个Rectangle类
    double width, length;
    static double A;
    double B;
    Rectangle(double x)  // 把两个变量初始化为相同传入值
        width = x;
        length = x;
        
    Rectangle(double w, double len)  // 分别对两个变量初始化不同的值
    width = w;
    length= len;
        
    public  double BRectangle() 
    B= (width + length) * 2;
    return B;
    public  double ARectangle() 
        A= width * length;
    return A;
public static void main(String[] args) 
 // 声明对象和创建对象double
    @SuppressWarnings("resource")
    Scanner sc = new Scanner(System.in);
    System.out.println("请输入矩形的w, len："); 
    int w = sc.nextInt();
    int len = sc.nextInt();
double c,s;Rectangle
Rectangle1 = new Rectangle(5, 6);Rectangle
Rectangle2 = new Rectangle(8);
c= Rectangle1.BRectangle();
s= Rectangle2.ARectangle();
System.out.println("周长是："+ c);
System.out.println("面积是："+ s);
System.out.println("矩形与圆的周长和为："+c);

    

    
class  Perimeter
         public static double getPerimeter(double width, double height) 
                return 2*(width + height);
         
        
            public static double getPerimeter(int r) 
                return 2*3.14*r;