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java中的各种集合排序_private string id

作者：小小林熬夜学编程 | 2024-04-17 11:51:36

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private string id

一、背景

1.软件开发过程中集合排序是比较强大的功能，会使用集合Map、Set、List实现排序功能，知道匿名内部类Comparator很关键，搞清楚集合排序的性能开销，排序遇到的坑以及解决的方法，注意下面的例子都是JDK1.8的用法。

二、LIst集合排序

1.UML类图

2.重点分析下ArrayList的排序，毕竟实战开发用的最频繁的就是它了

三、第一种做法

介绍：这种叫定制排序,或自定义排序,需编写匿名内部类,先new一个Comparator接口的比较器对象c,同时实现compare()其方法; 
然后将比较器对象c传给Collections.sort()方法的参数列表中,实现排序功能;一般用这种的比较多。

1.实体类（private int id）

  1. public class Person{
  2.     private int id;
  3.     private String name;
  4.     private String address;
  5.  
  6.     public Person(int id, String name, String address) {
  7.         this.id = id;
  8.         this.name = name;
  9.         this.address = address;
  10.     }
  11.  
  12.     public int getId() {
  13.         return id;
  14.     }
  15.  
  16.     public void setId(int id) {
  17.         this.id = id;
  18.     }
  19.  
  20.     public String getName() {
  21.         return name;
  22.     }
  23.  
  24.     public void setName(String name) {
  25.         this.name = name;
  26.     }
  27.  
  28.     public String getAddress() {
  29.         return address;
  30.     }
  31.  
  32.     public void setAddress(String address) {
  33.         this.address = address;
  34.     }
  35.  
  36.     @Override
  37.     public String toString() {
  38.         return "Person{" +
  39.                 "id='" + id + '\'' +
  40.                 ", name='" + name + '\'' +
  41.                 ", address='" + address + '\'' +
  42.                 '}';
  43.     }
  44. }

2.测试类

  1. public class ArrayListTest {
  2.     public static void main(String[] args) {
  3.         List<Person> list=Lists.newArrayList();
  4.         //产生10以内的随机数
  5.         int num = (int)(Math.random()*1000+1);
  6.         for(int i=num;i>0;i--){
  7.             list.add(new Person(i,"张三","河南"));
  8.         }
  9.         for(Object o : list){
  10.             System.out.println(o);
  11.         }
  12.         System.out.println("++++++++++++++++++++++++++++++++++++");
  13.         Collections.sort(list, new Comparator<Person>() {
  14.            @Override
  15.            public int compare(Person o1, Person o2) {
  16.                if (o1.getId() > o2.getId()) {
  17.                    return 1;
  18.                } else if (o1.getId() < o2.getId()) {
  19.                    return -1;
  20.                }
  21.                return 0;
  22.            }
  23.  
  24.        });
  25.         for(Object o : list){
  26.             System.out.println(o);
  27.         }
  28.     }
  29. }

3.结果（升序）

  1. Person{id='10', name='张三', address='河南'}
  2. Person{id='9', name='张三', address='河南'}
  3. Person{id='8', name='张三', address='河南'}
  4. Person{id='7', name='张三', address='河南'}
  5. Person{id='6', name='张三', address='河南'}
  6. Person{id='5', name='张三', address='河南'}
  7. Person{id='4', name='张三', address='河南'}
  8. Person{id='3', name='张三', address='河南'}
  9. Person{id='2', name='张三', address='河南'}
  10. Person{id='1', name='张三', address='河南'}
  11. ++++++++++++++++++++++++++++++++++++
  12. Person{id='1', name='张三', address='河南'}
  13. Person{id='2', name='张三', address='河南'}
  14. Person{id='3', name='张三', address='河南'}
  15. Person{id='4', name='张三', address='河南'}
  16. Person{id='5', name='张三', address='河南'}
  17. Person{id='6', name='张三', address='河南'}
  18. Person{id='7', name='张三', address='河南'}
  19. Person{id='8', name='张三', address='河南'}
  20. Person{id='9', name='张三', address='河南'}
  21. Person{id='10', name='张三', address='河南'}

四、第二中做法

1.实体类（private String id）

  1. public class Person{
  2.     private String id;
  3.     private String name;
  4.     private String address;
  5.  
  6.     public Person(String id, String name, String address) {
  7.         this.id = id;
  8.         this.name = name;
  9.         this.address = address;
  10.     }
  11.  
  12.     public String getId() {
  13.         return id;
  14.     }
  15.  
  16.     public void setId(String id) {
  17.         this.id = id;
  18.     }
  19.  
  20.     public String getName() {
  21.         return name;
  22.     }
  23.  
  24.     public void setName(String name) {
  25.         this.name = name;
  26.     }
  27.  
  28.     public String getAddress() {
  29.         return address;
  30.     }
  31.  
  32.     public void setAddress(String address) {
  33.         this.address = address;
  34.     }
  35.  
  36.     @Override
  37.     public String toString() {
  38.         return "Person{" +
  39.                 "id='" + id + '\'' +
  40.                 ", name='" + name + '\'' +
  41.                 ", address='" + address + '\'' +
  42.                 '}';
  43.     }
  44. }

2.测试类

  1. public class ArrayListTest {
  2.     public static void main(String[] args) {
  3.         List<Person> list=Lists.newArrayList();
  4.         //产生10以内的随机数
  5.         int num = (int)(Math.random()*100+1);
  6.         for(int i=num;i>0;i--){
  7.             list.add(new Person(""+i,"张三","河南"));
  8.         }
  9.         for(Object o : list){
  10.             System.out.println(o);
  11.         }
  12.         System.out.println("++++++++++++++++++++++++++++++++++++");
  13.        Collections.sort(list, new Comparator<Person>() {
  14.            @Override
  15.            public int compare(Person o1, Person o2) {
  16.                return  new Double(o1.getId()).compareTo(new Double(o2.getId()));
  17.            }
  18.  
  19.        });
  20.         for(Object o : list){
  21.             System.out.println(o);
  22.         }
  23.     }
  24. }

3.结果

  1. Person{id='10', name='张三', address='河南'}
  2. Person{id='9', name='张三', address='河南'}
  3. Person{id='8', name='张三', address='河南'}
  4. Person{id='7', name='张三', address='河南'}
  5. Person{id='6', name='张三', address='河南'}
  6. Person{id='5', name='张三', address='河南'}
  7. Person{id='4', name='张三', address='河南'}
  8. Person{id='3', name='张三', address='河南'}
  9. Person{id='2', name='张三', address='河南'}
  10. Person{id='1', name='张三', address='河南'}
  11. ++++++++++++++++++++++++++++++++++++
  12. Person{id='1', name='张三', address='河南'}
  13. Person{id='2', name='张三', address='河南'}
  14. Person{id='3', name='张三', address='河南'}
  15. Person{id='4', name='张三', address='河南'}
  16. Person{id='5', name='张三', address='河南'}
  17. Person{id='6', name='张三', address='河南'}
  18. Person{id='7', name='张三', address='河南'}
  19. Person{id='8', name='张三', address='河南'}
  20. Person{id='9', name='张三', address='河南'}
  21. Person{id='10', name='张三', address='河南'}

五、第三种做法

另外一种称为自然排序,参与排序的对象需实现comparable接口,重写其compareTo()方法,方法体中实现对象的比较大小规则。

1.实体类

  1. public class Person implements Comparable{
  2.     private String id;
  3.     private String name;
  4.     private String address;
  5.  
  6.     public Person(String id, String name, String address) {
  7.         this.id = id;
  8.         this.name = name;
  9.         this.address = address;
  10.     }
  11.  
  12.     public String getId() {
  13.         return id;
  14.     }
  15.  
  16.     public void setId(String id) {
  17.         this.id = id;
  18.     }
  19.  
  20.     public String getName() {
  21.         return name;
  22.     }
  23.  
  24.     public void setName(String name) {
  25.         this.name = name;
  26.     }
  27.  
  28.     public String getAddress() {
  29.         return address;
  30.     }
  31.  
  32.     public void setAddress(String address) {
  33.         this.address = address;
  34.     }
  35.  
  36.     @Override
  37.     public String toString() {
  38.         return "Person{" +
  39.                 "id='" + id + '\'' +
  40.                 ", name='" + name + '\'' +
  41.                 ", address='" + address + '\'' +
  42.                 '}';
  43.     }
  44.  
  45.     @Override
  46.     public int compareTo(Object o) {
  47.         if (o instanceof Person){
  48.             Person o1 = (Person)o;
  49.             return  new Double(this.getId()).compareTo(new Double(o1.getId()));
  50.         }
  51.         throw new ClassCastException("不能转换为Person类型的对象...");
  52.     }
  53. }

2.测试类

  1. public class ArrayListTest {
  2.     public static void main(String[] args) {
  3.         List<Person> list=Lists.newArrayList();
  4.         //产生10以内的随机数
  5.         int num = (int)(Math.random()*100+1);
  6.         for(int i=num;i>0;i--){
  7.             list.add(new Person(""+i,"张三","河南"));
  8.         }
  9.         for(Object o : list){
  10.             System.out.println(o);
  11.         }
  12.         System.out.println("++++++++++++++++++++++++++++++++++++");
  13.         Collections.sort(list);
  14.         for(Object o : list){
  15.             System.out.println(o);
  16.         }
  17.     }
  18. }

3.结果

  1. Person{id='10', name='张三', address='河南'}
  2. Person{id='9', name='张三', address='河南'}
  3. Person{id='8', name='张三', address='河南'}
  4. Person{id='7', name='张三', address='河南'}
  5. Person{id='6', name='张三', address='河南'}
  6. Person{id='5', name='张三', address='河南'}
  7. Person{id='4', name='张三', address='河南'}
  8. Person{id='3', name='张三', address='河南'}
  9. Person{id='2', name='张三', address='河南'}
  10. Person{id='1', name='张三', address='河南'}
  11. ++++++++++++++++++++++++++++++++++++
  12. Person{id='1', name='张三', address='河南'}
  13. Person{id='2', name='张三', address='河南'}
  14. Person{id='3', name='张三', address='河南'}
  15. Person{id='4', name='张三', address='河南'}
  16. Person{id='5', name='张三', address='河南'}
  17. Person{id='6', name='张三', address='河南'}
  18. Person{id='7', name='张三', address='河南'}
  19. Person{id='8', name='张三', address='河南'}
  20. Person{id='9', name='张三', address='河南'}
  21. Person{id='10', name='张三', address='河南'}

六、结束

今天就写到这吧，太困了，晚安！各位，希望能帮到你们。

Always keep the faith!!!

 

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