Java中的赋值运算符

自己做了一遍运行错误，于是放到Eclipse上运行发现是int there = one + two; there前没引用类型，有两点不能理解的是减等于和除等于和模等于的规律。。求解

public class HelloWorld{

    public static void main(String[] args) {

int one = 10 ;

        int two = 20 ;

        int three = 0 ;

        int there = one + two;

        System.out.println("there = one + two ==>" + there);

        there += one;

        System.out.println("there += one ==>" + there);

        there -= one;

        System.out.println("there -= one ==>" + there);

        there *= one;

        System.out.println("there *= one ==>" + there);

        there /= one;

        System.out.println("there /= one ==>" + there);

        there %= one;

        System.out.println("there %= one ==>" + there);