一些l练习about Java

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