如何对List集合中的数据进行排列

Question

[size=x-large]请问：怎样对List集合中的数据进行排序啊？？ 请给与详解！！！

谢谢[/size]

Answer 1

[size=large][color=red]要对List排序,你要对List里装的这种类型的类实现排序接口(Comparable).
举个例子:

下面这个例子是对List进行排序.使用Collections.sort(List list);方法,此方法会调用MyObject的compareTo方法.所以在MyObject类定义里要实现compareTo方法.
[code="java"]public class ListSort {

/**
 * main()
 * 2010-4-2,下午09:25:57
 */
public static void main(String[] args) {
    // TODO Auto-generated method stub
    List<MyObject> lists = new ArrayList<MyObject>();
    MyObject obj1 = new MyObject("d");
    MyObject obj2 = new MyObject("a");
    lists.add(obj1);
    lists.add(obj2);
    Collections.sort(lists);
    for (MyObject myObject : lists) {
        System.out.println(myObject.getContent());
    }
}

}
class MyObject implements Comparable{
private String content;
public MyObject(String _content) {
this.content = _content;
}

public String getContent() {
    return content;
}

public void setContent(String content) {
    this.content = content;
}

public int compareTo(MyObject obj) {
    // TODO Auto-generated method stub
    if (null == obj) return 1;
    else {
        return this.content.compareTo(obj.content);
    }

}

}[/code]

下面是Collections.sort方法
[code="java"]public static > void sort(List list) {
Object[] a = list.toArray();
Arrays.sort(a);
ListIterator i = list.listIterator();
for (int j=0; j<a.length; j++) {
i.next();
i.set((T)a[j]);
}
}[/code]

实际上我们的MyObject类的方法compareTo是在Arrays.sort()中被调用的...
请看..
[code="java"]public static void sort(Object[] a) {
Object[] aux = (Object[])a.clone();
mergeSort(aux, a, 0, a.length, 0);
}[/code]
[code="java"] private static void mergeSort(Object[] src,
Object[] dest,
int low,
int high,
int off) {
int length = high - low;

// Insertion sort on smallest arrays
    if (length < INSERTIONSORT_THRESHOLD) {
        for (int i=low; i<high; i++)
            for (int j=i; j>low &&
         ((Comparable) dest[j-1]).compareTo(dest[j])>0; j--)
                swap(dest, j, j-1);
        return;
    }

    // Recursively sort halves of dest into src
    int destLow  = low;
    int destHigh = high;
    low  += off;
    high += off;
    int mid = (low + high) >> 1;
    mergeSort(dest, src, low, mid, -off);
    mergeSort(dest, src, mid, high, -off);

    // If list is already sorted, just copy from src to dest.  This is an
    // optimization that results in faster sorts for nearly ordered lists.
    if (((Comparable)src[mid-1]).compareTo(src[mid]) <= 0) {
        System.arraycopy(src, low, dest, destLow, length);
        return;
    }

    // Merge sorted halves (now in src) into dest
    for(int i = destLow, p = low, q = mid; i < destHigh; i++) {
        if (q >= high || p < mid && ((Comparable)src[p]).compareTo(src[q])<=0)
            dest[i] = src[p++];
        else
            dest[i] = src[q++];
    }
}[/code][/color][/size]

当然,这是一种实现排序的办法.还有一种是实现Comparator,实现这个接口,然后使用
Collections.sort(List list,Comparator c);这个方法来排序..

原理差不多..

希望对你有帮助..