java Collections.sort() implements the default method and custom method of List sorting

1.Default list sorting method provided by java

Main code:

List list = new ArrayList();list.add("Liu Yuanyuan ");

list.add("Wang Shuo");
list.add("Li Ming");
list.add("Liu Di");
list. add("Liu Bu");

//Ascending order
Collections.sort(list,Collator.getInstance(java.util.Locale.CHINA));//Note: It is based on the pinyin of the Chinese characters Sorted alphabetically, rather than according to the general sorting method of Chinese characters
for(int i=0;i {
System.out.print(list.get( i));
}
        System.out.println("");

//Descending order
      Collections.reverse(list);//When no sorting rules are specified, it is also in accordance with Sorted alphabetically
                                                                                                                                         .

Output result:

李明Liu Bu Liu Di Liu Yuanyuan Wang Shuo

王 Shuo Liu Yuanyuan Liu Di Liu Bu Li Ming

2. Customized sorting rules:

The first is that the model class implements the Comparable interface and overrides the int compareTo(Object o) method

Model class:

public class StudentDTO implements Comparable

{

private String name;

private int age;

public String getName()
{

return name;

}

public void setName(String name)
{

this.name = name;

}

public ObjType getType()
{

  return type;

}

public void setAge(int age)
 {

 this.age= age;

 }

@ Override
public int compareTo(Object o)

{

StudentDTO sdto = (StudentDTO)o;

int otherAge = sdto.getAge();

// note : enum-type's comparison depend on types' list order of enum method

// so, if compared property is enum-type ,then its comparisonfollow ObjEnum.objType order

return this.age. compareTo(otherAge);

}

}

Main method:

public static void main(String[] args)

{

List studentList = new ArrayList();

StudentDTO s1 = new StudentDTO ();

s.setName("yuanyuan");

s.setAge(22);

studentList.add(s1);

StudentDTO s1 = new StudentDTO ();

s.setName("lily");

s.setAge( 23);

                                                    studentList.add(s2); ; //In descending order of age 23, 22

}

The second is that the comparator class implements the Comparator interface and overrides the int compare(Object o1, Object o2) method;

Model:

Public Class Studentdto Implements Comparable

{ Private String name; Prive In Age; AME (AME (AME )

{

        return name;

  }

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

     public ObjType getType()
     {
         return type;
     }

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

} 

           比较器类：

class MyCompartor implements Comparator
{
     @Override
     public int compare(Object o1, Object o2)
    {

           StudentDTO sdto1= (StudentDTO )o1;

           StudentDTO sdto2= (StudentDTO )o2;

           return sdto1.getAge.compareTo(stdo2.getAge())

    }
}

           主方法：

public static void main(String[] args)
{
      List studentList = new ArrayList();

      StudentDTO s1 = new StudentDTO ();

      s.setName("yuanyuan");

      s.setAge(22);

      studentList.add(s1);

      StudentDTO s1 = new StudentDTO ();

      s.setName("lily");

      s.setAge(23);

      studentList.add(s2);

      MyComparetor mc = new MyComparetor();

      Collections.sort(studentList,mc);     //按照age升序 22，23，

      Collections.reverse(studentList,mc);    //按照age降序 23,22   

}

 

 

附注：

1.对于数组的排序方法如下：

String[] names = {"王林",  "杨宝", "李镇", "刘迪", "刘波"};  
Arrays.sort(names, com.ibm.icu.text.Collator.getInstance(com.ibm.icu.util.ULocale.SIMPLIFIED_CHINESE));//升序;   
System.out.println(Arrays.toString(names));      

2.对于汉字的排序：可以尝试使用ICU4J会得到更好的结果，特别是姓为某些生僻字的时候，

用com.ibm.icu.text.Collator替换java.text.Collator，用com.ibm.icu.util.ULocale替换java.util.Locale

3.对于枚举类型的enum1.compareTo（enum2）是按照枚举类型值在定义时的先后顺序比较的，越后面的越大，

而不是按照值的字母先后顺序比较的。

 

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