对码输出的结果有些不解

        int one = 10 ;

        int two = 20 ;

        int three = 0 ;

        three = one + two;

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

        three += one;

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

        three -= one;

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

        three *= one;

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

        three /= one;

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

        three %= one;

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

输出的结果为：

three = one + two ==>30
three += one ==>40
three -= one ==>30
three *= one ==>300
three /= one ==>30
three %= one ==>0

倒数第二个结果不应该是3吗？three/=one不就是三十除十的结果吗？怎么是30呢？还有为什么每个输出的结果都是大于输出的值呢？