ComparatorFactory.java

package lambda;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

/**
 * Created by zzt on 5/25/15.
 * <p>
 * Description:
 */
public class ComparatorFa {
    public static Comparator<String> comparator1() {
        return (o1, o2) -> {
            Double d1 = Double.parseDouble(o1);
            Double d2 = Double.parseDouble(o2);
            return d1.compareTo(d2);
        };
    }

    public static Comparator<String> comparator2() {
        return (o1, o2) -> {
            Double d1 = Double.parseDouble(o1);
            Double d2 = Double.parseDouble(o2);
            return d1.compareTo(d2);
        };
    }

    public static Comparator<String> comparator3() {
        return (o1, o2) -> {
            Double d1 = Double.parseDouble(o1);
            Double d2 = Double.parseDouble(o2);
            return d1.compareTo(d2);
        };
    }

    public static void main(String[] args) {
        ArrayList list = new ArrayList<>();
        list.add(1.9);
        list.add(1.2);
        Collections.sort(list, comparator1());

    }
}

Notice that I doesn't add a type parameter to this list for in some place of real project (like DefaulRowSorter in swing, in my case) I can't using type parameter, which may hide some problems.