Using Collections.sort and Comparator in Java-优快云博客

本文详细介绍了如何在Java中利用Collections.sort()和Comparator接口实现对象的自定义排序，包括整数排序及不同属性的排序方法。

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Using Collections.sort and Comparator in Java

 
         package 
          de.vogella.algorithms.sort.standardjava; 
        
         import 
          java.util.ArrayList; 
        
         import 
          java.util.Collections; 
        
         import 
          java.util.List; 
        
         public 
          class 
         Simple { 
        
         public 
         static 
         void 
          main(String[] args) { 
        
         List list = 
         new 
         ArrayList(); 
        
         list.add(
         5
         ); 
        
         list.add(
         4
         ); 
        
         list.add(
         3
         ); 
        
         list.add(
         7
         ); 
        
         list.add(
         2
         ); 
        
         list.add(
         1
         ); 
        
         Collections.sort(list); 
        
         for 
         (Integer integer : list) { 
        
         System.out.println(integer); 
        
         } 
        
         } 
        
         }

This is possible because Integer implements the Comparable interface. This interface defines the method compare which performs pairwise comparison of the elements and returns -1 if the element is smaller then the compared element, 0 if it is equal and 1 if it is larger.

But what if what to sort differently, e.g. for example in different order. Well, you could just use Collection.reverse(). Or you define your own class with implements the interface Comparator.

         package 
          de.vogella.algorithms.sort.standardjava; 
        
         import 
          java.util.Comparator; 
        
         public 
          class 
         MyIntComparable 
         implements 
         Comparator<Integer>{ 
        
         @Override
        
         public 
         int 
         compare(Integer o1, Integer o2) { 
        
         return 
         (o1>o2 ? -
         1 
          : (o1==o2 ? 
         0 
         :  
         1
         )); 
        
         } 
        
         }

         package 
          de.vogella.algorithms.sort.standardjava; 
        
         import 
          java.util.ArrayList; 
        
         import 
          java.util.Collections; 
        
         import 
          java.util.List; 
        
         public 
          class 
         Simple2 { 
        
         public 
         static 
         void 
          main(String[] args) { 
        
         List<Integer> list = 
         new 
         ArrayList<Integer>(); 
        
         list.add(
         5
         ); 
        
         list.add(
         4
         ); 
        
         list.add(
         3
         ); 
        
         list.add(
         7
         ); 
        
         list.add(
         2
         ); 
        
         list.add(
         1
         ); 
        
         Collections.sort(list, 
         new 
         MyIntComparable()); 
        
         for 
         (Integer integer : list) { 
        
         System.out.println(integer); 
        
         } 
        
         } 
        
         }

The nice thing about this approach is that you then sort any object by any attribute or even a combination of attributes. For example if you have objects of type Person with an attribute income and dataOfBirth you could define different implementations of Comparator and sort the objects according to your needs.