Java stream 基于双精度值排序对象

Question

I have list of X1 objects and trying to sort the list based on method obj_function() which returns Double value.

result = custom_obj_list.stream()
    .sorted((x1,x2) -> {
        return -x1.obj_function().compareTo(x2.obj_function());
    }).filter((x2) -> { 
        return x2.obj_function <= 1; 
    }).collect(Collectors.toList());

But I'm struggling to solve the below error message

stream().sorted() cannot resolve symbol or cannot resolve method

Answer 1

You can use the Comparator.comparing instead of lambda expression, If you just want default sorting order

result = custom_obj_list.stream()
                        .sorted(Comparator.comparingDouble(X1::obj_function))  //X1 should be class name
                        .filter(x2 -> x2.obj_function() <= 1)
                        .collect(Collectors.toList());

or reverse sorting order

result = custom_obj_list.stream()
                        .sorted(Comparator.comparingDouble(X1::obj_function).reverse()))   ////X1 should be class name
                        .filter(x2 -> x2.obj_function() <= 1)
                        .collect(Collectors.toList());