Main.java

package com.company;

import java.util.Scanner;

public class Main {

    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);
        double a , b , c ;

        a = input.nextDouble();
        b = input.nextDouble();
        c = input.nextDouble();

        Triangle triangle1 = new Triangle();

        triangle1.setDimention(a,b,c);

        if (triangle1.do_exist(a,b,c))
        {
            System.out.println(triangle1.area());
        }
        else
        {
            System.out.println("No such triangle!");
        }

    }
}


Triangle class

package com.company;
import  java.lang.*;

public class Triangle {

    double _a = 0,_b = 0,_c = 0;

    boolean do_exist(double a, double b, double c)
    {
        boolean result  = a + b > c;

        result &= a + c > b;
        result &= b + c > a;

        if( result )
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    void setDimention(double a, double b, double c)
    {
        _a = a;
        _b = b;
        _c = c;
    }

    double peremeter()
    {
        double peremeter = _a + _b + _c;

        return peremeter;
    }

    double halfPeremeter()
    {
        double half_peremeter = peremeter() / 2;

        return half_peremeter;
    }

    double area()
    {
        double p = halfPeremeter();
        double area = Math.sqrt(p * (p - _a) * (p - _b) * (p - _c));

        return area;
    }
}