普林斯顿大学算法课 Algorithm Part I Week 3 比较器 Comparators

public interface Comparator<key>
            int compare(Key v, Key w)          //比较元素v和w

String[] a;  
...  
Arrays.sort();              //自然顺序（natural order）
...  
Arrays.sort(a, String.CASE_INSENSITIVE_ORDER);  
Arrays.sort(a, Collator.getInstance(new Locale("es"));  
Arrays.sort(a, new BritishPhoneBookOrder());                   //这三个顺序参数都是被Comparato<String>对象所定义的

public static void sort(Object[] a, Comparator comparator)
{
    int N = a.length;
    for (int i = 0; i < N;i++)
        for(int j =  i; j > 0 && less(comparator, a[j], a[j-1]); j--)
            exch(a, j, j-1);        
}

private static boolean less(Comparator c, Object v, Object w)
{    return c.compare(v, w) < 0;    }

private static void exch(Object[] a, int i, int j)
{    Object swap = a[i]; a[i] = a[j]; a[j] = swap;    }

public class Student 
{  
    public static final Comparator<Student> BY_NAME = new ByName();  
    public static final Comparator<Student> BY_SECTION = new BySection();  
    private final String name;  
    private final int section;  
    ...
    private static class ByName implements Comparator<Student>                        //ByName类实现了Comparator接口
    {
        public int compare(Student v, Student w)  
        {  return v.name.compareTo(w.name);  }  
    }  
   
    private static class BySection implements Comparator<Student>                     //BySection实现了Comparator接口
    {  
        public int compare(Student v, Student w)
        {  return v.section - w.section;  }  
    }  
}