求大神解答，如图，蟹蟹

[是酒酒呀]

用eclipse解答

[bcsflilong]

public class hhh {

	private static Scanner scanner=new Scanner(System.in);;

	public static void main(String[] args) {
	
		System.out.println("输入a边长:");
		String a = scanner.nextLine();
		double da=Double.parseDouble(a);
		System.out.println("输入b边长:");
		String b = scanner.nextLine();
		double db=Double.parseDouble(b);
		System.out.println("输入c边长:");
		String c = scanner.nextLine();
		
		double dc=Double.parseDouble(c);
		
		if ((da+db)>dc&&(da+dc)>db&&(db+dc)>da) {
			BigDecimal temp=new BigDecimal(a).add(new BigDecimal(b)).add(new BigDecimal(c));
			
			
			BigDecimal p=temp.divide(new BigDecimal(2), 2, BigDecimal.ROUND_HALF_UP);
			
			
			BigDecimal temp2=p.multiply(p.subtract(new BigDecimal(a))).multiply(p.subtract(new BigDecimal(b))).multiply(p.subtract(new BigDecimal(c)));
		
			
			
			double result=Math.sqrt(temp2.doubleValue());
			
			
			System.out.println("面积是："+result);
		}else {
			System.out.println("不是三角");
		}
		
	}

}

[十八道胡同]

package com.csnt.learn;

import java.util.Scanner;

/**
 * Hello world!
 *
 */
public class App 
{
    public static void main( String[] args )
    {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入a:");
        Double  a = Double.valueOf( sc.nextLine());
        System.out.println("请输入b:");
        Double  b = Double.valueOf( sc.nextLine());
        System.out.println("请输入c:");
        Double  c = Double.valueOf( sc.nextLine());

        double p=(a+b+c)*0.5;
        double result=Math.sqrt(p*(p-a)*(p-b)*(p-c));
        System.out.println(result);
    }

}