goldbach number

//Program 1 
import java.util.*;
class Goldbach //start of class
{
    void input()//start of input method
    {
        Scanner sc=new Scanner(System.in);
        int l,u,count1=0,count2=0;
        do{
            System.out.println("ENTER THE LOWER AND UPPER RANGE");
            l=sc.nextInt();
            u=sc.nextInt();
            if(l > u || l < 0 ||u < 0)
            System.out.println("WRONG INPUT. ENTER AGAIN.");
        }while(l  > u || l < 0 ||u < 0);
        for(int n=l; n <= u;n++)
        {
            if(n % 2 == 0)
            {
                count2++;
                if(count2== 1)
                System.out.println("THE GOLDBACH NUMBERS ARE AS FOLLOW:");
                for(int i=2;i <= (n/2);i++)
                {                    
                    if(isPrime(i) == true && isPrime(n-i) == true)
                    {
                        count1++;
                        if(count1==1)
                        System.out.println("PRIME PAIRS OF "+n+" ARE:\n"+i+", "+(n-i));
                        else if(count1 > 1)
                        System.out.println(i+", "+(n-i));
                    }
                }
                count1=0;
            }
        }
        System.out.println();
    }//end of input method
    boolean isPrime(int a)
    {
        for(int i=2;i <= (a/2);i++)
        {
            if(a % i==0)
            return false;
        }
        return true;
    }//end of isPrime method
}//end of class Goldbach
class Goldbach_Main
{
    public static void main(String args[])
    {
        Goldbach ob=new Goldbach();
        ob.input();
    }//end of main
}//end of class Goldbach_Main