用java求S=1+2+……+n的值

public class Test {
public static void main(String[] arges)
{
int n=20;
int sum=0;
for(int i=1;i<=n;i++)
{
sum+=i;
}
System.out.println(sum);
}

}

for(i=0,sun=0;i<=n;i++)
sun=sun+i;

for(i=0,s=0;i<n;s+=i,i++);

public class Ljh
{
int sum=0;
int n;
public static void main(String[] args)
{
Ljh zh=new Ljh();
zh.js(n)

}
public void js(int a)
{
int b=a;
for (int i=0;i<=b;i++)
{sum=sum+i;
}
System.out.println("1+2+3+...+n="+sum);
}

}

int reslut =0;
for(int i=1;i<=n;i++){
result+=i;
}