Java Arraylist 如何使用 Comparator排序

Java Arraylist 如何使用 Comparator排序import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

public class Sort implements Comparator<String> {
private final static int UP = 1;

private final static int DOWM = -1;

private int state;

public Sort(int state) {
this.state = state;
}

public Sort() {

}

public int compare(String o1, String o2) {
if (state == Sort.DOWM) {
return sortDown(o1, o2);
}
return sortUp(o1, o2);
}

private int sortUp(String o1, String o2) {
if (o1.compareTo(o2) < 0) {
return -1;
} else if (o1.compareTo(o2) > 0) {
return 1;
} else {
return 0;
}
}

private int sortDown(String o1, String o2) {
if (o1.compareTo(o2) > 0) {
return -1;
} else if (o1.compareTo(o2) < 0) {
return 1;
} else {
return 0;
}
}

public static void main(String[] args) {
ArrayList<String> array = new ArrayList<String>();
array.add("000001");
array.add("000003");
array.add("000005");
array.add("000004");
array.add("000002");
Collections.sort(array, new Sort(Sort.DOWM));

for (String str : array) {
System.out.println(str);
}
}
}



==============

功能：ArrayList中放置他是HashMap对象，这时要对其中的所有对象做排序。

一、首先编写排序器

DataComparator.java

import Comparable.test1.Person;
import java.util.Comparator;
import java.util.HashMap;
import java.text.Collator;
import java.text.CollationKey;

public class DataComparator
     implements Comparator {
   Collator collator = Collator.getInstance(); //调入这个是解决中文排序问题
   public int compare(Object obj1, Object obj2) {
     HashMap map1 = (HashMap) obj1;
     HashMap map2 = (HashMap) obj2;
     String name1 = (String) map1.get("Name");
     String name2 = (String) map2.get("Name");
     CollationKey key1 = collator.getCollationKey(name1.toLowerCase());
     CollationKey key2 = collator.getCollationKey(name2.toLowerCase());
     return key1.compareTo(key2);
   }
}

二、测试

ArrayListMapSortTest.java

import java.util.Collections;
import Comparable.ArrayListMapSort.DataComparator;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import java.util.Iterator;
import java.util.Date;
import java.io.File;

public class ArrayListMapSortTest {

   //列出文件夹下的文件及文件夹，不包括子文件夹中的文件和文件夹
   public ArrayList listFoldersAndFiles(String path) {
     File file = new File(path);
     File[] list = file.listFiles();
     ArrayList al = new ArrayList();
     for (int i = 0; i < list.length; i++) {
       //if (list[i].isDirectory())
       //     listFolder(list[i].getPath());
       HashMap hm = new HashMap();
       hm.put("Name", list[i].getName());
       hm.put("Path", list[i].getPath());
       hm.put("AbsolutePath", list[i].getAbsolutePath());
       hm.put("Parent", list[i].getParent());
//           hm.put("isAbsolute", list[i].isAbsolute());
//           hm.put("isDirectory", list[i].isDirectory());
//           hm.put("isFile", list[i].isFile());
//           hm.put("isHidden", list[i].isHidden());
       hm.put("lastModified",
              new Date(list[i].lastModified()).toLocaleString());
       al.add(hm);
       //System.out.println(list[i].getName()+"    是文件夹："+list[i].isDirectory());
     }
     return al;
   }

   public static void main(String[] args) {
     ArrayListMapSortTest databean = new ArrayListMapSortTest();
     ArrayList al = databean.listFoldersAndFiles("F:\\");
     Collections.sort(al, new DataComparator());
     for (int i = 0; i < al.size(); i++) {
       HashMap hm = (HashMap) al.get(i);
       for (Iterator iter = hm.entrySet().iterator(); iter.hasNext(); ) {
         Map.Entry entry = (Map.Entry) iter.next();
         Object key = entry.getKey();
         Object val = entry.getValue();
         System.out.print(key + "    " + val + "   ");
       }
       System.out.println();
     }
   }
}