java怎么像pyhton一样赋值给字符串运算呀

比如
double currentweight =122.5
double new weight = 60
weight = newweight - current weight
输出System .out println(weight)
这样是算不出的，怎么让他能够计算出来

double currentweight =122.5
double newweight = 60
double  weight = newweight - currentweight

 double currentWeight = 122.5;
    double newWeight = 60;
    System.out.println(newWeight - currentWeight);

或者
double currentWeight = 122.5;
double newWeight = 60;
double weight = newWeight - currentWeight;
System.out.println(weight);