Question

I have this class:

public class Friend {

private String name;
private String location;
private String temp;
private String humidity;

public String getTemp() {
    return temp;
}

public void setTemp(String temp) {
    this.temp = temp;
}

public String getHumidity() {
    return humidity;
}

public void setHumidity(String humidity) {
    this.humidity = humidity;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}


public String getLocation() {
    return location;
}

public void setLocation(String location) {
    this.location = location;
}
}

I want to sort a List based on name, location, temp and humidity based on user input.

EDIT:The user specifies by which data member the sorting has to be done.

What is the easiest way to do this?

Thank you.

Answer 1

Java has a static function called Collections.sort(List, Comparator) which sorts a (generified) List of objects given a custom Comparator which, given two objects of the same type, determines which one is ordered before the other.

Your task is to write a function which creates a Comparator which orders the objects based on its arguments and the user specified sort order. For example:

public Comparator<Friend> getComparator(final String sortBy) {
  if ("name".equals(sortBy)) {
    return new Comparator<Friend>() {
      @Override int compare(Friend f1, Friend f2) 
        return f1.getName().compareTo(f2.getName());
      }
    };
  } else if ("location".equals(sortBy)) {
    return new Comparator<Friend>() {
      @Override int compare(Friend f1, Friend f2) 
        return f1.getLocation().compareTo(f2.getLocation());
      }
    };
  } else if ("temp".equals(sortBy)) {
    // ...
  } else {
    throw new IllegalArgumentException("invalid sort field '" + sortBy + "'");
  }
}