java类如何按照某一属性排序

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1. 首先Person类，实现可按照属性name或者age排序，Personl类如下：

class Person{      public String name;      public  int age;            public Person(String name, int age) {          super();          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;      }      @Override      public String toString() {          return "Person [name=" + name + ", age=" + age + "]";      }  }

2.首先看示例：利用Collections.sort方法实现对String,Integer...等等类型的排序

public class T1 {            public static void main(String[] args) {                    List<String> list=new ArrayList<String>();          list.add("d");          list.add("f");          list.add("a");          sortString(list);                    System.out.println("===========");                    List<Integer> list2=new ArrayList<Integer>();          list2.add(9);          list2.add(5);          list2.add(8);          sortInteger(list2);      }            public static void sortString(List<String> list){          Collections.sort(list);                    for (String string : list) {              System.out.println(string);          }      }      public static void sortInteger(List<Integer> list){          Collections.sort(list);                    for (Integer integer : list) {              System.out.println(integer);          }      }  }

3.试试对Person类进行排序

public class T2 {            public static void main(String[] args) {                    List<Person> list=new ArrayList<Person>();            Person p1=new Person("d",55);          Person p2=new Person("c",18);          Person p3=new Person("a",37);                    list.add(p1);          list.add(p2);          list.add(p3);          sortPerson(list);      }            public static void sortPerson(List<Person> list){          Collections.sort(list);//编译不通过!!!!      }  }

编译器提示"The method sort(List<T>) in the type Collections is not applicable for the arguments (List<Person>)"

要想使用Collections.sort进行排序该class 必须实现Comparable<Person>接口，并覆写compareTo方法；现在对Person类进行改造：

class Person implements Comparable<Person>{      public String name;      public  int age;            public Person(String name, int age) {          super();          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;      }      @Override      public String toString() {          return "Person [name=" + name + ", age=" + age + "]";      }      @Override      public int compareTo(Person o) {          return this.getName().compareTo(o.getName());      }  }

再次测试：

public class T2 {            public static void main(String[] args) {                    List<Person> list=new ArrayList<Person>();            Person p1=new Person("d",55);          Person p2=new Person("c",18);          Person p3=new Person("a",37);                    list.add(p1);          list.add(p2);          list.add(p3);          sortPerson(list);      }            public static void sortPerson(List<Person> list){          Collections.sort(list);//编译通过；          for (Person person : list) {              System.out.println(person);          }      }  }

输出结果：

Person [name=a, age=37]  Person [name=c, age=18]  Person [name=d, age=55]

4.以上代码中实现了按照name属性对List<Person>排序，如果想按照age属性排序，需要修改>compareTo方法如下：

   @Override      public int compareTo(Person o) {          return new Integer(this.getAge()).compareTo(o.getAge());      }

再次运行main方法测试结果如下：

Person [name=c, age=18]  Person [name=a, age=37]  Person [name=d, age=55]

5.其他实现方式(1):Person类可以不实现Comparable<T>接口，而是调用public static <T> void sort(List<T> list, Comparator<? super T> c)方法实现排序。

public static void sortPerson(List<Person> list){          Collections.sort(list,new Comparator<Person>() {              @Override              public int compare(Person o1, Person o2) {                  return o1.getName().compareTo (o2.getName());              }          });                    for (Person person : list) {              System.out.println(person);          }      }

6.其他实现方式(2):Person类可以不实现Comparable<T>接口，而是通过自定义比较器类的方式实现排序。比较器代码如下：

// 自定义比较器：按name比较 class NameComparator implements Comparator<Person> {        @Override      public int compare(Person o1, Person o2) {          return o1.getName().compareTo(o2.getName());        }    }      // 自定义比较器：按age比较    class AgeComparator implements Comparator<Person> {        public int compare(Person object1, Person object2) {// 实现接口中的方法            return new Integer(object1.getAge()).compareTo(object2.getAge());      }    }

比较器使用方式如下：

public class T2 {            public static void main(String[] args) {                    List<Person> list=new ArrayList<Person>();            Person p1=new Person("d",55);          Person p2=new Person("c",18);          Person p3=new Person("a",37);                    list.add(p1);          list.add(p2);          list.add(p3);          sortPerson(list);      }            public static void sortPerson(List<Person> list){                    Collections.sort(list,new NameComparator());          for (Person person : list) {              System.out.println(person);          }      }  }

运行结果如下:

Person [name=a, age=37]  Person [name=c, age=18]  Person [name=d, age=55]

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