java.util.Comparator in Java8

SortLexicographicOrder.java

import java.util.*;

public class SortLexicographicOrder {
  public static void main(String[] args) {
    Person[] people = {
      new Person("C", "F", 30),
      new Person("B", "M", 40),
      new Person("D", "M", 20),
      new Person("B", "F", 40),
      new Person("A", "F", 20)
    };

    if (true) {
      // Java8
      Arrays.sort(people,
        Comparator.comparingInt(Person::getAge)
                  .thenComparing(Person::getName)
                  .thenComparing(Person::getGender));
    } else {
      // Java7
      Arrays.sort(people,
        new Comparator<Person>() {
          @Override
          public int compare(Person o1, Person o2) {
            int ret;
            ret = Integer.compare(o1.getAge(), o2.getAge());
            if (ret != 0)
              return ret;
            ret = o1.getName().compareTo(o2.getName());
            if (ret != 0)
              return ret;
            return o1.getGender().compareTo(o2.getGender());
          }
        });
    }
    
    for (Person e : people)
      System.out.println(e);
  }
}

class Person {
  private final String name;
  private final String gender;
  private final int age;
  public Person(String n, String g, int a) {
    name = n;
    gender = g;
    age = a;
  }
  public String getName() { return name; }
  public String getGender() { return gender; }
  public int getAge() { return age; }
  public String toString() {
    return "{"+name+","+gender+","+age+"}";
  }
}

SortNullable.java

import java.util.*;

public class SortNullable {
  public static void main(String[] args) {
    Item[] items = {
      new Item("B", null),
      new Item("A", "y"),
      new Item("A", null),
      new Item("A", "x"),
      new Item("B", "y")
    };

    if (true) {
      // Java8
      Arrays.sort(items,
        Comparator.comparing(Item::getCode)
                  .thenComparing(Item::getSubCode, Comparator.nullsLast(Comparator.naturalOrder())));
    } else {
      // Java7
      Arrays.sort(items,
        new Comparator<Item>() {
          @Override
          public int compare(Item o1, Item o2) {
            int ret;
            ret = o1.getCode().compareTo(o2.getCode());
            if (ret != 0)
              return ret;
            String subCode1 = o1.getSubCode();
            String subCode2 = o2.getSubCode();
            if (subCode1 == null) {
              if (subCode2 == null)
                ret = 0;  // null == null
              else
                ret = 1;  // null > o2
            } else {
              if (subCode2 == null)
                ret = -1;  // o1 < null
              else
                ret = subCode1.compareTo(subCode2);
            }
            return ret;
          }
        });
    }
    
    for (Item e : items)
      System.out.println(e);
  }
}

class Item {
  private final String code;
  private final String subCode;
  public Item(String c, String sc) {
    code = c;
    subCode = sc;
  }
  public String getCode() { return code; }
  public String getSubCode() { return subCode; }
  public String toString() {
    return "{"+code+","+subCode+"}";
  }
}

SortReverse.java

import java.util.*;

public class SortReverse {
  public static void main(String[] args) {
    String[] a = {"D", "B", "A", "C"};
    
    if (true) {
      // Java8
      Arrays.sort(a, Comparator.reverseOrder());
    } else {
      // Java7
      Arrays.sort(a,
        new Comparator<String>() {
          @Override
          public int compare(String o1, String o2) {
            return o2.compareTo(o1);
          }
        });
    }
    
    for (String e : a)
      System.out.println(e);
  }
}

http://d.hatena.ne.jp/yohhoy/20141007/p1 (ja)