Sort List> based on value

Question

Basically I have a List>, and I want to sort it by the values of certain key in the map.

The problem is that I do not know

Answer 1

First you will have to define the desired order, especially the place of the string values, or are they all numbers in text form?

Then implement a more complex comparator method, working through your comparison criteria from highest to lowest priority.

Untested:

 List> list = new ArrayList<>();
    Collections.sort(list, (map1, map2) -> {
      Object v1 = map1.get("Field1");
      Object v2 = map2.get("Field1");

      // --------------------------------------------
      // handle null
      // --------------------------------------------
      if(v1 == null && v2 == null) {
        return 0;
      }

      if(v1 == null && v2 != null) {
        return -1 /* null value before non-null value */;
      }

      if(v1 != null && v2 == null) {
        return 1 /* non-null value after null value */;
      }

      // --------------------------------------------
      // handle String
      // --------------------------------------------
      boolean v1IsString = v1 instanceof String;
      boolean v2IsString = v2 instanceof String;
      if(v1IsString && v2IsString) {
        return ((String) v1).compareToIgnoreCase((String) v2);
      }

      if(v1IsString && !v2IsString) {
        return -1 /* string value before non-string values */;
      }

      if(!v1IsString && v2IsString) {
        return 1 /* non-string value after string value */;
      }

      // --------------------------------------------
      // handle LocalDate
      // --------------------------------------------
      // ....

      // --------------------------------------------
      // handle Instant
      // --------------------------------------------
      // ....

      // --------------------------------------------
      // handle BigDecimal and BigInteger
      // --------------------------------------------
      // ....

      // --------------------------------------------
      // handle Number
      // --------------------------------------------
      boolean v1IsNumber = v1 instanceof Number;
      boolean v2IsNumber = v2 instanceof Number;
      if(v1IsNumber && v2IsNumber) {
        double d1 = ((Number) v1).doubleValue();
        double d2 = ((Number) v2).doubleValue();
        return (int) Math.signum(d1 - d2);
      }

      if(v1IsNumber && !v2IsNumber) {
        return -1 /* number value before non-number values */;
      }

      if(!v1IsNumber && v2IsNumber) {
        return 1 /* non-number value after number value */;
      }

      // etc.

      // --------------------------------------------
      // finally, treat all unhandled value types as equal
      // --------------------------------------------
      return 0;
    });