java时间倒叙排序 java按时间排序文件

转载

mob64ca140ac564 2024-08-19 09:53:07

文章标签 java时间倒叙排序 Java C# C++ C 文章分类 Java 后端开发

简单类型的排序

简单类型不外是byte, char, short, int, long, float, double等数据类型，这些类型不能放在集中，只能使用数组。 java.util.Arrays方法提供了对这些类型的sort方法（实际上还有很多其他有用的方法），下面是对一个简单的int数组排序：

int[] arr = {2, 3, 1,10,7,4}; 
 System.out.print("before sort: "); 
 for (int i = 0; i< arr.length; i++) 
 System.out.print(arr[i] + " "); 
 System.out.println(); 
 Arrays.sort(arr); 
 System.out.print("after sort: "); 
 for (int i = 0; i< arr.length; i++) 
 System.out.print(arr[i] + " "); 
 System.out.println(); 
输出结果： 
before sort: 2 3 1 10 7 4 
after sort: 1 2 3 4 7 10

我们看到排序结果是按照升序排列的，下面的排序都是如此。

对象的排序

对象可以放在数组里，同样调用Arrays.sort(Object[] arr)即可；也可以放到集里，用java.util.Collections的
sort(List list)。
但是这个类必须实现了java.lang.Comparable接口。这个接口只有一个方法：int compartTo(Object o)，
当本对象比传入的对象大时，返回一个正整数。以类Programmer为例：

class Programmer implements Comparable{ 
 private String name; 
 private String language; 
 private double pay; 
 public Programmer(String name, String language, double pay) { 
 this.name = name; 
 this.language = language; 
 this.pay = pay; 
 } 
 public int compareTo(Object o) { 
 Programmer other = (Programmer)o; 
 return (int)pay - (int)other.pay; 
 } 
 public String toString(){ 
 return "{name: " + name + ", language: " + language + ", money: " + pay + "}"; 
 }
 }

对其进行排序：

ArrayList list = new ArrayList(); 
 list.add(new Programmer("张三", "C", 12000)); 
 list.add(new Programmer("李四", "Java", 200)); 
 list.add(new Programmer("王五", "C++", 5000)); 
 list.add(new Programmer("钱六", "VB", 3000)); 
 System.out.println("before sort: " + list); 
 Collections.sort(list); 
 System.out.println("after sort: " + list);

输出：

before sort: [{name: 张三, language: C, money: 12000.0}, {name: 李四, language: Java, money: 200.0},  
 {name: 王五, language: C++, money: 5000.0}, {name: 钱六, language: VB, money: 3000.0}]  
after sort: [{name: 李四, language: Java, money: 200.0}, {name: 钱六, language: VB, money: 3000.0},  
{name: 王五, language: C++, money: 5000.0}, {name: 张三, language: C, money: 12000.0}]

够简单吧！查查Comparable的javadoc可以知道，有很多类已经实现了该接口，因此对这些类的排序几行代码就可以搞定。

最近看C#发现其中用System.Array.sort对数组排序，适用于所有实现了IComparable接口的对象，看来微软的借鉴能力还真是强啊！

对已有类进行排序

上面的方法有一个问题，就是一个类已经存在了，并且没有实现Comparable接口，使用一个子类进行封装？

很麻烦（你可以对下面的例子试试）。还有一种情况就是对一个类没法实现多种排序。以File类为例，它实现了Comparable接口，

但是是按照名称排序的。如果要按照大小排序，或者按修改时间排序呢？对这两种情况，使用java.util包的Comparator接口：

Arrays.sort(Object[] arr, Comparator com)

Collections.sort(Object[] arr, Comparator com)

Comparator接口的方法：

public int compare(Object o1, Object o2) 当o1比o2大时返回一个正整数

public boolean equals(Object obj) 判断obj与这个Comparator是否同一个对象

下面使用Comparator对文件实现了按文件大小或修改时间排序：

class FileUtils { 
 static class CompratorByLastModified implements Comparator { 
 public int compare(Object o1, Object o2) { 
 File file1 = (File)o1; 
 File file2 = (File)o2; 
 long diff = file1.lastModified() - file2.lastModified(); 
 if (diff > 0) 
 return 1; 
 else if (diff == 0) 
 return 0; 
 else 
 return -1; 
 } 
 public boolean equals(Object obj){ 
 return true; //简单做法 
 } 
 } 
 static class CompratorBySize implements Comparator { 
 public int compare(Object o1, Object o2) { 
 File file1 = (File)o1; 
 File file2 = (File)o2; 
 long diff = file1.length() - file2.length(); 
 if (diff > 0) 
 return 1; 
 else if (diff == 0) 
 return 0; 
 else 
 return -1; 
 } 
 public boolean equals(Object obj){ 
 return true; //简单做法 
 } 
 } 
}

调用的示例：

File dir = new File("C:\\temp"); 
 File[] files = dir.listFiles(); 
 System.out.print("before sort: "); 
 for (int i = 0; i< files.length; i++) 
 System.out.print(files[i] + " "); 
 System.out.println(); 
 Arrays.sort(files); 
 System.out.print("sort by name: "); 
 for (int i = 0; i< files.length; i++) 
 System.out.print(files[i] + " "); 
 System.out.println(); 
 Arrays.sort(files, new FileUtils.CompratorBySize()); 
 System.out.print("sort by size: "); 
 for (int i = 0; i< files.length; i++) 
 System.out.print(files[i] + " "); 
 System.out.println(); 
 Arrays.sort(files, new FileUtils.CompratorByLastModified()); 
 System.out.print("sort by last modified: "); 
 for (int i = 0; i< files.length; i++) 
 System.out.print(files[i] + " "); 
 System.out.println();

自己找个目录试一下吧。用这些Java类库中的方法，一般情况下应该是不用自己写排序算法了吧？

最后附上完整代码占点版面：

import java.io.*; 
import java.util.*; 
public class TestSort { 
 public static void main(String[] args) { 
 sortSimpleType(); 
 sortComparable(); 
 sortComparator(); 
 } 
 public static void sortSimpleType() { 
 int[] arr = {2, 3, 1,10,7,4}; 
 System.out.print("before sort: "); 
 for (int i = 0; i< arr.length; i++) 
 System.out.print(arr[i] + " "); 
 System.out.println(); 
 Arrays.sort(arr); 
 System.out.print("after sort: "); 
 for (int i = 0; i< arr.length; i++) 
 System.out.print(arr[i] + " "); 
 System.out.println(); 
 } 
 public static void sortComparable() { 
 ArrayList list = new ArrayList(); 
 list.add(new Programmer("张三", "C", 12000)); 
 list.add(new Programmer("李四", "Java", 200)); 
 list.add(new Programmer("王五", "C++", 5000)); 
 list.add(new Programmer("钱六", "VB", 3000)); 
 System.out.println("before sort: " + list); 
 Collections.sort(list); 
 System.out.println("after sort: " + list); 
 } 
 public static void sortComparator() { 
 File dir = new File("C:\\java"); 
 File[] files = dir.listFiles(); 
 System.out.print("before sort: "); 
 for (int i = 0; i< files.length; i++) 
 System.out.println(files[i] + " "); 
 System.out.println(); 
 Arrays.sort(files); 
 System.out.print("sort by name: "); 
 for (int i = 0; i< files.length; i++) 
 System.out.println(files[i] + " "); 
 System.out.println(); 
 Arrays.sort(files, new FileUtils.CompratorBySize()); 
 System.out.print("sort by size: "); 
 for (int i = 0; i< files.length; i++) 
 System.out.println(files[i] + " "); 
 System.out.println(); 
 Arrays.sort(files, new FileUtils.CompratorByLastModified()); 
 System.out.print("sort by last modified: "); 
 for (int i = 0; i< files.length; i++) 
 System.out.println(files[i] + " "); 
 System.out.println(); 
 } 
} 
class Programmer implements Comparable{ 
 private String name; 
 private String language; 
 private double pay; 
 public Programmer(String name, String language, double pay) { 
 this.name = name; 
 this.language = language; 
 this.pay = pay; 
 } 
 public int compareTo(Object o) { 
 Programmer other = (Programmer)o; 
 return (int)pay - (int)other.pay; 
 } 
 public String toString(){ 
 return "{name: " + name + ", language: " + language + ", money: " + pay + "}"; 
 } 
} 
class FileUtils { 
 static class CompratorByLastModified implements Comparator { 
 public int compare(Object o1, Object o2) { 
 File file1 = (File)o1; 
 File file2 = (File)o2; 
 long diff = file1.lastModified() - file2.lastModified(); 
 if (diff > 0) 
 return 1; 
 else if (diff == 0) 
 return 0; 
 else 
 return -1; 
 } 
 public boolean equals(Object obj){ 
 return true; //简单做法 
 } 
 } 
 static class CompratorBySize implements Comparator { 
 public int compare(Object o1, Object o2) { 
 File file1 = (File)o1; 
 File file2 = (File)o2; 
 long diff = file1.length() - file2.length(); 
 if (diff > 0) 
 return 1; 
 else if (diff == 0) 
 return 0; 
 else 
 return -1; 
 } 
 public boolean equals(Object obj){ 
 return true; //简单做法 
 } 
 } 
} 
运行结果： 
C:\java>java TestSort 
before sort: 2 3 1 10 7 4 
after sort: 1 2 3 4 7 10 
before sort: [{name: 张三, language: C, money: 12000.0}, {name: 李四, language: 
Java, money: 200.0}, {name: 王五, language: C++, money: 5000.0}, {name: 钱六, language: VB, money: 3000.0}] 
after sort: [{name: 李四, language: Java, money: 200.0}, {name: 钱六, language: 
VB, money: 3000.0}, {name: 王五, language: C++, money: 5000.0}, {name: 张三, language: C, money: 12000.0}] 
before sort: C:\java\class.bat 
C:\java\onlyfun 
C:\java\build.xml 
C:\java\1.txt 
C:\java\native.bat 
C:\java\hib.bat 
C:\java\hjar 
C:\java\src 
C:\java\xdoclet 
C:\java\lib2 
C:\java\jsf.bat 
C:\java\struts.bat 
C:\java\TestSort.java 
C:\java\TestSort.class 
C:\java\jar 
C:\java\messages_zh_TW1.properties 
C:\java\messages.properties 
C:\java\messages_zh_TW.properties 
C:\java\Programmer.class 
C:\java\FileUtils$CompratorByLastModified.class 
C:\java\FileUtils$CompratorBySize.class 
C:\java\FileUtils.class 
C:\java\lib 
C:\java\bean.xml 
sort by name: C:\java\1.txt 
C:\java\bean.xml 
C:\java\build.xml 
C:\java\class.bat 
C:\java\FileUtils$CompratorByLastModified.class 
C:\java\FileUtils$CompratorBySize.class 
C:\java\FileUtils.class 
C:\java\hib.bat 
C:\java\hjar 
C:\java\jar 
C:\java\jsf.bat 
C:\java\lib 
C:\java\lib2 
C:\java\messages.properties 
C:\java\messages_zh_TW.properties 
C:\java\messages_zh_TW1.properties 
C:\java\native.bat 
C:\java\onlyfun 
C:\java\Programmer.class 
C:\java\src 
C:\java\struts.bat 
C:\java\TestSort.class 
C:\java\TestSort.java 
C:\java\xdoclet 
sort by size: C:\java\hjar 
C:\java\jar 
C:\java\lib 
C:\java\lib2 
C:\java\onlyfun 
C:\java\src 
C:\java\xdoclet 
C:\java\1.txt 
C:\java\native.bat 
C:\java\jsf.bat 
C:\java\struts.bat 
C:\java\class.bat 
C:\java\FileUtils.class 
C:\java\hib.bat 
C:\java\messages.properties 
C:\java\FileUtils$CompratorBySize.class 
C:\java\FileUtils$CompratorByLastModified.class 
C:\java\bean.xml 
C:\java\Programmer.class 
C:\java\messages_zh_TW.properties 
C:\java\messages_zh_TW1.properties 
C:\java\build.xml 
C:\java\TestSort.class 
C:\java\TestSort.java 
sort by last modified: C:\java\lib 
C:\java\jar 
C:\java\hjar 
C:\java\onlyfun 
C:\java\1.txt 
C:\java\hib.bat 
C:\java\src 
C:\java\xdoclet 
C:\java\build.xml 
C:\java\lib2 
C:\java\bean.xml 
C:\java\class.bat 
C:\java\struts.bat 
C:\java\messages.properties 
C:\java\messages_zh_TW1.properties 
C:\java\messages_zh_TW.properties 
C:\java\jsf.bat 
C:\java\native.bat 
C:\java\TestSort.java 
C:\java\FileUtils.class 
C:\java\FileUtils$CompratorBySize.class 
C:\java\FileUtils$CompratorByLastModified.class 
C:\java\Programmer.class 
C:\java\TestSort.class 
C:\java>

本文章为转载内容，我们尊重原作者对文章享有的著作权。如有内容错误或侵权问题，欢迎原作者联系我们进行内容更正或删除文章。