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;

                         }

                     });