Java语言程序设计基础篇第四章课后习题（保持更新）

package com.Wyhon.test;

import java.util.*;
import java.text.*;

public abstract class Rectangle {

public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter the length from the center to a vertex: ");
double r = input.nextDouble();

DecimalFormat df = new DecimalFormat("#.00");
System.out.println("The area of the pentagon is: " + df.format(GetArea(r)));
}

public static double GetArea(double r) {
double frameLength = 2 * r * Math.sin(Math.PI / 5);
double area = 5 * Math.pow(frameLength, 2) / (4 * Math.tan(Math.PI / 5));
return area;
}

}

package com.Wyhon.test;

import java.util.*;
import java.text.*;

public class Rectangle {

public static void main(String[] args) {

Scanner input = new Scanner(System.in);

System.out.print("Enter point 1 (latitude and longitute) in degrees: ");
String s1 = input.nextLine();

System.out.print("Enter point 2 (latitude and longitute) in degrees: ");
String s2 = input.nextLine();

GetDistance(s1, s2);
}

public static void GetDistance(String s1, String s2) {
final double r = 6371.01;

String[] _s1 = s1.split(",");
String[] _s2 = s2.split(",");

double x1 = Math.toRadians(Double.parseDouble(_s1[0]));
double y1 = Math.toRadians(Double.parseDouble(_s1[1]));
double x2 = Math.toRadians(Double.parseDouble(_s2[0]));
double y2 = Math.toRadians(Double.parseDouble(_s2[1]));

double distance = r * Math.acos(Math.sin(x1) * Math.sin(x2) + Math.cos(x1) * Math.cos(x2) * Math.cos(y1 - y2)) ;

System.out.println("The distance between the two points is " + distance + " Km");
}
}

package com.Wyhon.test;

import java.util.Scanner;
import java.text.*;

public class test1 {

public static void main(String[] args) {

Scanner input = new Scanner(System.in);
System.out.print("Enter the side: ");
double s = input.nextDouble();

DecimalFormat df = new DecimalFormat("#.00");
System.out.println("The area of the hexagon is " + df.format(GetArea(s)));
}

public static double GetArea(double s) {

double area = 6 * Math.pow(s, 2) / (4 * Math.tan(Math.PI / 6));
return area;
}

}

package com.Wyhon.test;

import java.util.Scanner;
import java.text.*;

public class test1 {

public static void main(String[] args) {

Scanner input = new Scanner(System.in);
System.out.print("Enter a character: ");
String str = input.next();

if(str.length() != 1) {
System.out.println("You must enter an exact character!");
System.exit(1);
}

char ch = str.charAt(0);
System.out.println("The Unicode for the character " + ch + " is " + (int) ch);
}

}