Java this 作用

/**
* Created by sanmao on 2016/7/8.
*/
public class sum {
private int i;
public  void ssum(){
int s=0;
for (int j = 1; j <i; j++) {
s+=j;
}
System.out.println(s);
}
public void setI(int i){
this.i=i;
}
public int getI(){
return i;
}

public static void main(String[] args) {
Scanner cin=new Scanner(System.in);
System.out.println("输入一个大于1的整数：");
int i=cin.nextInt();
sum s=new sum();
s.setI(i);
s.ssum();
}
}