java學習(十六)：對象的自訂比較，Comparator和Comparable

標籤：

通過兩個例子實現對象的自訂排序

1、實現Comparator介面。

 1 import java.util.ArrayList; 2 import java.util.Collections; 3 import java.util.Comparator; 4 import java.util.List; 5  6 public class StudentComparator implements Comparator<Object> 7 { 8     @Override 9     public int compare(Object arg0, Object arg1)10     {11         return ((Student)arg0).getId() - ((Student)arg1).getId();12     }13     14     public static void main(String[] args)15     {16         Student stu1 = new Student(11, "A");17         Student stu2 = new Student(33, "B");18         Student stu3 = new Student(22, "C");19         Student stu4 = new Student(55, "D");20         List<Student> stuList = new ArrayList<Student>(4);21         stuList.add(stu1);22         stuList.add(stu2);23         stuList.add(stu3);24         stuList.add(stu4);25         Collections.sort(stuList, new StudentComparator());26         System.out.println(stuList);27     }28 }29 30 class Student31 {32     private int id;33     34     private String name;35     36     public Student(int id, String name)37     {38         this.id = id;39         this.name = name;40     }41     42     public int getId()43     {44         return id;45     }46     47     public void setId(int id)48     {49         this.id = id;50     }51     52     public String getName()53     {54         return name;55     }56     57     public void setName(String name)58     {59         this.name = name;60     }61     62     public String toString()63     {64         return this.getId() + this.getName();65     }66 }

輸出：[11A, 22C, 33B, 55D]

 

2、在需要排序的類上直接實現Comparable介面

 1 import java.util.ArrayList; 2 import java.util.Collections; 3 import java.util.List; 4  5 public class Student implements Comparable<Object> 6 { 7     private int id; 8      9     private String name;10     11     public Student(int id, String name)12     {13         this.id = id;14         this.name = name;15     }16     17     public int getId()18     {19         return id;20     }21     22     public void setId(int id)23     {24         this.id = id;25     }26     27     public String getName()28     {29         return name;30     }31     32     public void setName(String name)33     {34         this.name = name;35     }36     37     public String toString()38     {39         return this.getId() + this.getName();40     }41     42     @Override43     public int compareTo(Object o)44     {45         return this.getId() - ((Student)o).getId();46     }47     48     public static void main(String[] args)49     {50         Student stu1 = new Student(11, "A");51         Student stu2 = new Student(33, "B");52         Student stu3 = new Student(22, "C");53         Student stu4 = new Student(55, "D");54         List<Student> stuList = new ArrayList<Student>(4);55         stuList.add(stu1);56         stuList.add(stu2);57         stuList.add(stu3);58         stuList.add(stu4);59         Collections.sort(stuList);60         System.out.println(stuList);61     }62     63 }

 

同樣輸出：[11A, 22C, 33B, 55D]

 

3、一個類實現了Comparable介面則表明這個類自身對象之間是可以相互比較的，這個類對象組成的集合就可以直接使用sort方法排序。

　　Comparator可以看成一種演算法的實現，將演算法和資料分離。Comparator也可以在下面兩種環境下使用：

　　（1）類的設計師沒有考慮到比較問題而沒有實現Comparable，可以通過Comparator來實現排序而不必改變對象本身。

　　（2）可以使用多種排序標準，比如定義升序類、降序類等。

java學習(十六)：對象的自訂比較，Comparator和Comparable