Java语言程序设计基础篇 第八章 课后编程答案

ch0801

import java.util.Scanner;

public class ch0801{
  public static void main( String[] args ){
    Rectangle r1 = new Rectangle(4,40) ;
    Rectangle r2 = new Rectangle(3.5,35.9) ;
    System.out.println("Rectangle1 : width = " + r1.width + " , height = " + r1.height + " , area = " + r1.getArea() + " , perimeter = " + r1.getPerimeter() ) ;
    System.out.println("Rectangle2 : width = " + r2.width + " , height = " + r2.height + " , area = " + r2.getArea() + " , perimeter = " + r2.getPerimeter() ) ;

  }
}

class Rectangle{
  double width ;
  double height ;
  Rectangle(){
    width = height = 1 ;
  }
  Rectangle( double w , double h ){
    width = w ;
    height = h ;
  }
  double getArea(){
    return width*height ;
  }
  double getPerimeter(){
    return (width+height)*2 ;
  }
}

ch0802

import java.util.Scanner;

public class ch0802{
  public static void main( String[] args ){
    Stock myStock = new Stock("JAVA","Sum Microsystems Inc") ;
    myStock.setPreviousClosingPrice(4.5) ;
    myStock.setCurrentPrice(4.35) ;
    System.out.println("Has changed " + myStock.getChangePerent() ) ;
  }
}

class Stock{
  private String symbol ;
  private String name ;
  private double previousClosingPrice ;
  private double currentPrice ;
  Stock(){

  }
  Stock( String symbol , String name ){
    this.symbol = symbol ;
    this.name = name ;
  }
  double getChangePerent(){
    return (currentPrice-previousClosingPrice)/previousClosingPrice ;
  }
  void setPreviousClosingPrice( double previousClosingPrice ){
    this.previousClosingPrice = previousClosingPrice ;
  }
  void setCurrentPrice( double currentPrice ){
    this.currentPrice = currentPrice ;
  }
}

ch0803

import java.util.Date;
public class ch0803{
  public static void main( String[] args ){
    Date date = new Date() ;
    long goesTime = 10000 ;
    int times = 1 ;
    while( times <= 8 ){
      date.setTime(goesTime);
      System.out.println(date.toString()) ;
      goesTime = goesTime * 10 ;
      times++ ;
    }
  }
}

ch0804

import java.util.Random;

public class ch0804{
  public static void main( String[] args ){
    Random random = new Random(1000) ;
    int i = 0 ;
    while( i < 50 ){
      int x = random.nextInt(100) ;
      System.out.println(x) ;
      ++i ;
    }
  }
}

ch0805

import java.util.GregorianCalendar;

public class ch0805{
  public static void main( String[] args ){
    myGregorianCalendar calendar = new myGregorianCalendar() ;
    calendar.show_date() ;
    calendar.set(123456789765L) ;
    calendar.show_date() ;
  }
}

class myGregorianCalendar{
  private GregorianCalendar ca ;
  private int year ;
  private int month ;
  private int day ;
  myGregorianCalendar(){
    ca = new GregorianCalendar() ;
    year = ca.get(GregorianCalendar.YEAR) ;
    month = ca.get(GregorianCalendar.MONTH) + 1 ;
    day = ca.get(GregorianCalendar.DAY_OF_MONTH) ;
  }
  void show_date(){
    System.out.println( "Current date is " + month + " " + day + ", " + year ) ;
  }
  void set( long d ){
    ca.setTimeInMillis(d) ;
    year = ca.get(GregorianCalendar.YEAR) ;
    month = ca.get(GregorianCalendar.MONTH) + 1 ;
    day = ca.get(GregorianCalendar.DAY_OF_MONTH) ;
  }
}

ch0806

import java.util.Scanner;
import javax.swing.JOptionPane;

public class ch0806 {
    public static void main(String[] args) {

        PrintCalendar myCalendar = new PrintCalendar() ;

        myCalendar.print() ;

    }
}

class PrintCalendar{
    int year ;
    int month ;
    // static String output ;
    PrintCalendar(){

        Scanner in = new Scanner(System.in) ;

        System.out.print("Enter Year : ") ;

        year = in.nextInt() ;

        System.out.print("Enter Month: ") ;

        month = in.nextInt() ;

    }
    void print(){
        int st = this.getFirst() ;
        String output = "" ;
        output += "      " + monthInEnglish() + ", " + year + "\n" ;
        output += "-------------------------------\n" ;
        output += " Sum Mon Tue Wed Thu Fri Sat\n" ;
        int days = getMonthDays() ;
        int p_day = 1 ;
        for( int i = 0 ; i < st ; ++i ){
            output += "    " ;
        }
        while( st <= 6 ){
            output += "   " + p_day ;
            p_day++ ;
            st++ ;
        }
        output += "\n" ;
        while( true ){
            for( int i = 0 ; i < 7 ; ++i ){
                output += "  " + (p_day<10?(" "+p_day):(p_day)) ;
                p_day++ ;
                if( p_day > days )
                    break ;
            }
            output += "\n" ;
            if( p_day > days )
                break ;
        }
        System.out.println(output);
    }
    int getFirst(){
        int c ;
        int y ;
        int m ;
        int d = 1 ;
        if( month >= 3 ){
            m = month ;
            c = year/100 ;
            y = year%100 ;
        }
        else{
            m = 12 + month ;
            c = (year-1)/100 ;
            y = (year-1)%100 ;
        }
        int w = y + y/4 + c/4 - 2*c + 26*(m+1)/10 + d - 1 ;
        w = w % 7 ;
        if( w < 0 ) w += 7 ;
        return w ;
    }
    String monthInEnglish(){
        String[] m = { "" , "January" , "February" , "March" , "April" , "May" , "June" , "July" , "August" , "September" , "October" , "November" , "December" } ;
        return m[month] ;
    }
    int getMonthDays(){
        if( month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12 )
            return 31 ;
        if( month != 2 )
            return 30 ;
        if( year % 4 == 0 && ( year % 100 != 0 || year % 400 == 0 ) )
            return 29 ;
        return 28 ;
    }
}

ch0807

import java.util.Date;
import java.util.Scanner;

public class ch0807{
  public static void main( String[] args ){
    Account myAccount = new Account(1122,20000) ;
    myAccount.setAnnualInterestRate(4.5) ;
    myAccount.withDraw(2500) ;
    myAccount.deposit(3000) ;
    System.out.println( "balance =: " + myAccount.getBalance()) ;
    System.out.println( "MonthlyTnterest =: " + myAccount.getMonthlyTnterest()) ;
    System.out.println(myAccount.getDateCreated()) ;
  }
}

class Account{
  private int id ;
  private double balance ;
  private double annualInterestRate ;
  Date dateCreated ;
  Account(){
    id = 0 ;
    balance = annualInterestRate = 0 ;
    dateCreated = new Date() ;
  }
  Account( int id , double balance ){
    this.id = id ;
    this.balance = balance ;
    annualInterestRate = 0 ;
    dateCreated = new Date() ;
  }
  int getId(){
    return id ;
  }
  double getBalance(){
    return balance ;
  }
  double getAnnualInterestRate(){
    return annualInterestRate ;
  }
  void setId( int id ){
    this.id = id ;
  }
  void setBalance( double balance ){
    this.balance = balance ;
  }
  void setAnnualInterestRate( double annualInterestRate ){
    this.annualInterestRate = annualInterestRate ;
  }
  Date getDateCreated(){
    return dateCreated ;
  }
  double getMonthlyTnterest(){
    return balance * (annualInterestRate/1200) ;
  }
  void withDraw( double num ){
    balance -= num ;
  }
  void deposit( double num ){
    balance += num ;
  }
}

ch0808

public class ch0808{
  public static void main( String[] args ){
    Fan fan1 = new Fan() ;
    fan1.setSpeed(3) ;
    fan1.setRadius(10) ;
    fan1.setColor("yellow") ;
    fan1.setOn(true) ;
    Fan fan2 = new Fan() ;
    fan2.setSpeed(2) ;
    fan2.setRadius(5) ;
    fan2.setColor("blue") ;
    fan2.setOn(false) ;
    System.out.println("fan1:\n" + fan1.tostring()) ;
    System.out.println("fan2:\n" + fan2.tostring()) ;
  }
}

class Fan{
  public static int SLOW = 1 ;
  public static int MEDIUM = 2 ;
  public static int FAST = 3 ;
  private int speed ;
  private boolean on ;
  private double radius ;
  String color ;
  Fan(){
    speed = SLOW ;
    on = false ;
    radius = 5 ;
    color = "blue" ;
  }
  int getSpeed(){
    return speed ;
  }
  void setSpeed( int speed ){
    this.speed = speed ;
  }
  boolean getOn(){
    return on ;
  }
  void setOn( boolean on ){
    this.on = on ;
  }
  double getRadius(){
    return radius ;
  }
  void setRadius( double radius ){
    this.radius = radius ;
  }
  String getColor(){
    return color ;
  }
  void setColor( String color ){
    this.color = color ;
  }
  String tostring(){
    if( on )
      return "Fan is on and:\nNow speed is " + speed + "\nColor is " + color + "\nRadius is " + radius + "\n" ;
    else
      return "Fan is off and:\nColor is " + color + "\nRadius is " + radius + "\n" ;
  }

}

ch0809

import java.util.Scanner;

public class ch0809{
  public static void main( String[] args ){
    RegularPolygon re1 = new RegularPolygon() ;
    RegularPolygon re2 = new RegularPolygon(6,4) ;
    RegularPolygon re3 = new RegularPolygon(10,4,5.6,7.8) ;
    System.out.println( "re1 perimeter is: " + re1.getPerimeter() ) ;
    System.out.println( "re1 area is: " + re1.getArea() ) ;
    System.out.println( "re2 perimeter is: " + re2.getPerimeter() ) ;
    System.out.println( "re2 area is: " + re2.getArea() ) ;
    System.out.println( "re3 perimeter is: " + re3.getPerimeter() ) ;
    System.out.println( "re3 area is: " + re3.getArea() ) ;
  }
}

class RegularPolygon{
  private int n ;
  private double side ;
  private double x ;
  private double y ;
  RegularPolygon(){
    this.n = 3 ;
    this.side = 1 ;
    this.x = 0 ;
    this.y = 0 ;
  }
  RegularPolygon( int n , double side ){
    this.x = y = 0 ;
    this.n = n ;
    this.side = side ;
  }
  RegularPolygon( int n , double side , double x , double y ){
    this.n = n ;
    this.side = side ;
    this.x = x ;
    this.y = y ;
  }
  int getN(){
    return n ;
  }
  double getSide(){
    return side ;
  }
  double getX(){
    return x ;
  }
  double getY(){
    return y ;
  }
  void setN( int n ){
    this.n = n ;
  }
  void setSide( double side ){
    this.side = side ;
  }
  void setX( double x ){
    this.x = x ;
  }
  void setY( double y ){
    this.y = y ;
  }
  double getPerimeter(){
    return n * side ;
  }
  double getArea(){
    return n*side*side/4/Math.tan(side) ;
  }
}

ch0810

import java.util.Scanner;
public class ch0810{
  public static void main( String[] args ){
    Scanner in = new Scanner(System.in) ;
    System.out.print("Enter a, b, c: ") ;
    double a = in.nextDouble() ;
    double b = in.nextDouble() ;
    double c = in.nextDouble() ;
    QuadraticEquation qua = new QuadraticEquation(a,b,c) ;
    System.out.println("Discriminant is: "+qua.getDiscriminant()) ;
    if( qua.getDiscriminant() >= 0 ){
      System.out.println("Root1 is: " + qua.getRoot1() ) ;
      System.out.println("Root2 is: " + qua.getRoot2() ) ;
    }
  }
}

class QuadraticEquation{
  private double a ;
  private double b ;
  private double c ;
  QuadraticEquation( double a , double b , double c ){
    this.a = a ;
    this.b = b ;
    this.c = c ;
  }
  double getA(){
    return a ;
  }
  double getB(){
    return b ;
  }
  double getC(){
    return c ;
  }
  double getDiscriminant(){
    return b*b - 4*a*c ;
  }
  double getRoot1(){
    if( this.getDiscriminant() < 0 )
      return 0 ;
    return (-b+Math.sqrt(this.getDiscriminant()))/(2*a) ;
  }
  double getRoot2(){
    if( this.getDiscriminant() < 0 )
      return 0 ;
    return (-b+Math.sqrt(this.getDiscriminant()))/(2*a) ;
  }
}

ch0811

import java.util.Scanner;
public class ch0811{
  public static void main( String[] args ){
    Scanner in = new Scanner(System.in) ;
    System.out.println("Enter a, b, c, d, e, f: ") ;
    double a = in.nextDouble() ;
    double b = in.nextDouble() ;
    double c = in.nextDouble() ;
    double d = in.nextDouble() ;
    double e = in.nextDouble() ;
    double f = in.nextDouble() ;
    LinearEquation line = new LinearEquation(a,b,c,d,e,f) ;
    if( line.isSolvable() == false )
      System.out.println("The equation has no solution.") ;
    else
      System.out.println("X = " + line.getX() + " , Y = " + line.getY() ) ;
  }
}

class LinearEquation{
  private double a ;
  private double b ;
  private double c ;
  private double d ;
  private double e ;
  private double f ;
  LinearEquation(double a, double b, double c, double d, double e, double f){
    this.a = a ;
    this.b = b ;
    this.c = c ;
    this.d = d ;
    this.e = e ;
    this.f = f ;
  }
  boolean isSolvable(){
    if( (a*d - b*c) != 0 )
      return true ;
    return false ;
  }
  double getX(){
    return (e*d-b*f)/(a*d-b*c) ;
  }
  double getY(){
    return (a*f-e*c)/(a*d-b*c) ;
  }
}

ch0812

import java.util.Scanner;

public class ch0812{
  public static void main( String[] args ){
    double sx , sy , ex , ey ;
    line l1 = new line() ;
    line l2 = new line() ;
    Scanner in = new Scanner(System.in) ;
    System.out.print("Enter the endpoints of the first line segment:" ) ;
    sx = in.nextDouble() ;
    sy = in.nextDouble() ;
    ex = in.nextDouble() ;
    ey = in.nextDouble() ;
    l1.set(sx,sy,ex,ey);
    System.out.print("Enter the endpoints of the second line segment:" ) ;
    sx = in.nextDouble() ;
    sy = in.nextDouble() ;
    ex = in.nextDouble() ;
    ey = in.nextDouble() ;
    l2.set(sx,sy,ex,ey) ;
    l1.show_crosser_with(l2) ;
  }
}

class line{
  private double sx ;
  private double sy ;
  private double ex ;
  private double ey ;
  line(){
    this.sx = 0 ;
    this.sy = 0 ;
    this.ex = 0 ;
    this.ey = 0 ;
  }
  void set( double sx , double sy , double ex , double ey ){
    this.sx = sx ;
    this.sy = sy ;
    this.ex = ex ;
    this.ey = ey ;
  }
  void show_crosser_with( line line2 ){
    double k1 = (ey-sy)/(ex-sx) ;
    double k2 = (line2.ey-line2.sy)/(line2.ex-line2.sx) ;
    if( k1 == k2 ){
      System.out.println( "These two lines are parallel to each other !" ) ;
    }
    else{
      double csx , csy ;
      double b1 = sy - k1*sx ;
      double b2 = line2.sy - k2*line2.sx ;
      csx = (b2-b1)/(k1-k2) ;
      csy = k1*(b2-b1)/(k1-k2) + b1 ;
      System.out.println( "The intersecting point is: (" + csx + ", " + csy + ")" ) ;
    }
  }
}

ch0813

import java.util.Scanner;

public class ch0813{
  static int r , c ;
  public static void main( String[] args ){
    Scanner in = new Scanner(System.in) ;
    System.out.print("Enter the number of rows and columns of the array: ") ;
    r = in.nextInt() ;
    c = in.nextInt() ;
    double[][] a = new double[r][c] ;
    for( int i = 0 ; i < r ; ++i ){
      for( int j = 0 ; j < c ; ++j ){
        a[i][j] = in.nextDouble() ;
      }
    }
    Location locat = new Location() ;
    locat = locateLargest(a) ;
    System.out.println("The location of the largest element is " + locat.maxValue + " at (" + locat.row + ", " + locat.column + ")");
  }

  public static Location locateLargest( double[][] a ){
    Location locat = new Location() ;
    locat.maxValue = -0xffffff ;
    for( int i = 0 ; i < r ; ++i ){
      for( int j = 0 ; j < c ; ++j ){
        if( a[i][j] > locat.maxValue ){
          locat.maxValue = a[i][j] ;
          locat.row = i ;
          locat.column = j ;
        }
      }
    }
    return locat ;
  }
}

class Location{
  public int row ;
  public int column ;
  public double maxValue ;
}