一些l练习about Java

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1.函数求回文数

import java.util.Scanner;public class huiwen {public static void main(String[] args){    Scanner in=new Scanner(System.in);    int n=in.nextInt();    reverse(n);}public static void reverse(int number){while(number>0){System.out.print(number%10);number/=10;}}}

运行结果：

1234
4321

2.判断三条边能否组成三角形，如果可以并求其面积

import java.util.Scanner;public class sanjiaoxing {public static void main(String[] args) { Scanner in=new Scanner(System.in);     double A,B,C;     System.out.println("please input three number: ");     A=in.nextInt();     B=in.nextInt();     C=in.nextInt();     if(isValid(A,B,C))     {     System.out.println("This is a true Triangle!");     System.out.println(area(A,B,C));     }     else      {     System.out.println("NO a Triangle!");     }     }     public static boolean isValid(double side1,double side2,double side3)     {     if((side1+side2>side3)||(side1+side3>side2)||(side2+side3>side1))     return true;     else     return false;      }     public static double area(double side1,double side2,double side3)     {      double p,S;      p=(side1+side2+side3)/2;      S=Math.sqrt(p*(p-side1)*(p-side2)*(p-side3));      return S;     }}

运行结果：

please input three number:
2 5 6
This is a true Triangle!
4.683748498798798

3.用函数求等边多边形的面积

import java.util.Scanner;public class hjy {public static void main(String[] args) {Scanner input = new Scanner(System.in);         System.out.println("please enter side: ");        double s = input.nextDouble();            int number = input.nextInt();         System.out.println(area(number, s));  }public static double area(int n, double side)  {      double S;      S = n * side * side / (4 * Math.tan(Math.PI / n));      return S;  }  }

运行结果：

please enter side:
5 12
279.9038105676658

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