java API提供的方法实现排序 如file按日期和大小排序
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
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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；也可以放到聚集里，用java.util.Collections的sort(List list)。注意不是list必须实现List接口而不仅仅是Collection接口。
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
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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？
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?最后附上完整代码占点版面：
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TestSort.javaimport 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:\\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(); }}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 }}?
学习了，谢谢LZ分享