Java中的sort

Java中对集合排序有两种方式

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

 /**
  * @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;
     }
 }

Comparable

 /**
  * @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;
     }
 }

Comparator

  * 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;
                         }
                     });