排序集合的對象 (Sorting objects of the Collection)

• This concept is related to sorting and here we will see how to sort objects on the Collection?

  這個概念與排序有關，在這里我們將看到如何對Collection上的對象進行排序？

• In java, we have utility class Collections which provide various methods to perform various task and one of the methods of Collection class is related to sorting like sort().

  在Java中，我們有實用程序類Collections，它提供了執(zhí)行各種任務的各種方法，并且Collection類的方法之一與sort()之類的排序有關。

• We can implement sorting on Collection object in two ways:

  我們可以通過兩種方式對Collection對象實施排序：

• By using Comparable
• By using Comparator

• When we call Collections.sort(). It sorts an object based on natural sorting or default sorting(i.e Ascending order) that's is specified in compareTo() method.

  當我們調用Collections.sort()時 。 它根據(jù)compareTo()方法中指定的自然排序或默認排序(即升序)對對象進行排序。

• When we call Collections.sort(Comparator). It sorts an object based on customized sorting (i.e Ascending order or Descending order) that's is specified in compare() method of Comparator.

  當我們調用Collections.sort(Comparator)時 。 它根據(jù)在Comparator的compare()方法中指定的自定義排序(即升序或降序)對對象進行排序。

We will see the sorting ways one by one...

我們將一一看到排序方式...

1)通過使用比較器 (1) By using Comparator)

• If we pass the Comparator object in Collection class constructor then our compare() method will be executed.

  如果我們在Collection類構造函數(shù)中傳遞Comparator對象，則將執(zhí)行compare()方法。

• When we want customize sorting then we should go for Comparator.

  當我們想要自定義排序時，我們應該選擇比較器。

• It is possible to implement customized sorting by using Comparator interface. (Customized sorting means that according to our need whether it is ascending or descending).

  使用Comparator接口可以實現(xiàn)自定義排序。 (自定義排序意味著根據(jù)我們的需要是升序還是降序)。

Example:

例：

import java.util.*;class TreeSetClass {public static void main(String[] args) {// Here we are passing Comparator object in Collection // class constructor for custoize sortingTreeSet ts = new TreeSet(new CustomizeSorting());// adding elements to TreeSetts.add(10);ts.add(40);ts.add(30);ts.add(20);// Customized Sorted ListSystem.out.println("Customize sorting :" + ts);} }// Here we are implementing Comparator interface class CustomizeSorting implements Comparator {// Here we are overrding compare() method of Comparatorpublic int compare(Object obj1, Object obj2) {Integer i1 = (Integer) obj1;Integer i2 = (Integer) obj2;return -i1.compareTo(i2);} }

Output

輸出量

E:\Programs>javac TreeSetClass.javaE:\Programs>java TreeSetClass Customize sorting :[40, 30, 20, 10]

2)使用可比接口 (2) By using Comparable interface)

• For predefined Comparable classes default natural sorting is already available.

  對于預定義的可比較類，默認的自然排序已可用。

• For predefined Non-Comparable classes default natural sorting is not already available.

  對于預定義的“不可比較”類，默認自然排序尚不可用。

• For our customized classes to define natural sorting then we should go for Comparable.

  為了讓我們的自定義類定義自然排序，我們應該選擇Comparable。

• In case of default natural sorting compulsory object should be homogenous and Comparable otherwise we will get CCE (ClassCastException).

  在默認情況下，自然排序強制對象應該是同質且可比較的，否則我們將獲得CCE(ClassCastException)。

Example:

例：

import java.util.*;class TreeSetClass {public static void main(String[] args) {Student s1 = new Student(10);Student s2 = new Student(30);Student s3 = new Student(70);Student s4 = new Student(20);// Here we are not passing Comparator object in Collection // class constructor for default sortingTreeSet ts = new TreeSet();// adding elements to TreeSetts.add(s1);ts.add(s2);ts.add(s3);ts.add(s4);// Customized Sorted ListSystem.out.println("Default sorting :" + ts);} }// Here we are implementing Comparable interface class Student implements Comparable {int code;Student(int code) {this.code = code;}public String toString() {return " Code - " + code;}// Here we are overrding compare() method of Comparable interfacepublic int compareTo(Object obj) {int code1 = this.code;Student intermediate = (Student) obj;int code2 = intermediate.code;if (code1 < code2)return -1;else if (code1 > code2)return +1;elsereturn 0;} }

Output

輸出量

E:\Programs>javac TreeSetClass.javaE:\Programs>java TreeSetClass Default sorting :[ Code - 10, Code - 20, Code - 30, Code - 70]

翻譯自: https://www.includehelp.com/java/how-to-sort-objects-of-the-collection-in-java.aspx

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