[java-基础拓展]-Java sort集合排序的两种方式解析

1、Comparable和Comparator

public static <T> void sort(List<T> list); 将集合中的数据按照默认规则进行排序 (我们在自己的类里面实现Comparabl接口方法compareTo)
public static <T> void sort(List<T> list, Comparator<? super T>); 将集合中的数据按照指定规则进行排序

2、Comparable

/**
 * @author gw
 * @date 2019/11/5 0005 下午 22:15
 */

/*
 * public static<T> void sort(List<T> list); 将集合中的数据按照默认规则进行排序
 *
 * 注意:
 *   sort使用前提:被排序的集合里面存储的元素,必须实现Comparable(接口),重写接口中的方法compareTo,定义排序规则
 *
 *   升序: this - 参数
 *      return 0;就是按照原来顺序输出
 *
 *
 * */
public class Demo02Sort {
  public static void main(String[] args) {
    ArrayList<Person> objects = new ArrayList<>();
    objects.add(new Person("小明", 23));
    objects.add(new Person("小红", 24));
    objects.add(new Person("小绿", 22));

    System.out.println("objects = " + objects);
    Collections.sort(objects);
    System.out.println("objects = " + objects);
  }
}


class Person implements Comparable<Person> {
  private String name;
  private int age;

  @Override
  public int compareTo(Person person) {
//    return 0;
    return this.getAge() - person.getAge();

  }

  @Override
  public String toString() {
    return "Person{" +
        "name='" + name + '\'' +
        ", age=" + age +
        '}';
  }

  public Person() {
  }

  public Person(String name, int age) {
    this.name = name;
    this.age = age;
  }

  public String getName() {
    return name;
  }

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

  public int getAge() {
    return age;
  }

  public void setAge(int age) {
    this.age = age;
  }
}

3、Comparator

/**
 * @author gw
 * @date 2019/11/5 0005 下午 22:40
 */


/*
 * Comparator
 * Comparable都是接口
 *
 * public static <T> void sort(List<T> list, Comparator<? super T> c)
 *
 * Comparable: 我们的类继承Comparable接口,然后实现里面的CompareTo方法,
 *       如何调用:Collections.sort(arrayList)
 *
 * Comparator: 我们的类不用继承Comparable接口,也不用继承Comparator接口
 *       如何调用:Collections.sort(objects, new Comparator<Person1>() { // 匿名类
            @Override
            public int compare(Person1 person1, Person1 t1) {
              int res = person1.getAge() - t1.getAge();
              // 前面减去后面,升序排列
              if (res == 0) {
                return person1.getName().charAt(0) - t1.getName().charAt(0);
              }
              return res;
            }
          });
 *
 * */
public class Demo03SortComparator {
  public static void main(String[] args) {
    ArrayList<Person1> objects = new ArrayList<>();
    objects.add(new Person1("b小明", 23));
    objects.add(new Person1("小红", 24));
    objects.add(new Person1("小绿", 22));
    objects.add(new Person1("a小绿", 23));

    System.out.println("objects = " + objects);
    Collections.sort(objects, new Comparator<Person1>() {
      @Override
      public int compare(Person1 person1, Person1 t1) {
//        return 0;
        int res = person1.getAge() - t1.getAge();

        // 前面减去后面,升序排列
        if (res == 0) {
          return person1.getName().charAt(0) - t1.getName().charAt(0);
        }
        return res;
      }
    });
    System.out.println("objects = " + objects);
  }
}


class Person1 {
  private String name;
  private int age;


  @Override
  public String toString() {
    return "Person{" +
        "name='" + name + '\'' +
        ", age=" + age +
        '}';
  }

  public Person1() {
  }

  public Person1(String name, int age) {
    this.name = name;
    this.age = age;
  }

  public String getName() {
    return name;
  }

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

  public int getAge() {
    return age;
  }

  public void setAge(int age) {
    this.age = age;
  }
}

4、Comparable和Comparator调用方法

* Comparable: 我们的类继承Comparable接口,然后实现里面的CompareTo方法,
 *       如何调用:Collections.sort(arrayList)
 *
 * Comparator: 我们的类不用继承Comparable接口,也不用继承Comparator接口
 *       如何调用:Collections.sort(objects, new Comparator<Person1>() { // 匿名类
            @Override
            public int compare(Person1 person1, Person1 t1) {
              int res = person1.getAge() - t1.getAge();
              // 前面减去后面,升序排列
              if (res == 0) {
                return person1.getName().charAt(0) - t1.getName().charAt(0);
              }
              return res;
            }
          });