Set和SortedSet

The asterisk on HashSet indicates that, in the absence of other constraints, this should be your default choice because it is optimized for speed.


对hashCode( )的定义在后面
对hashed & tree必须写 equals( )方法
但是hashCode( )只有在使用HashSet/LinkedHashSet的时候才需要 (HashSet经常被用到since that should generally be your first choice as a Set implementation)
//However, for good programming style, you should always override hashCode( ) when you override equals( ).

sorted set

因为其中的元素是排好序的,所以会有一些额外的功能
Comparator comparator( ): Produces the Comparator used for this Set, or null for natural ordering.
Object first( ): 最小值
Object last( ): 最大值
SortedSet subSet(fromElement, toElement): 生成此set的子集,[from,to)
SortedSet headSet(toElement): 子集:由小于toElement的元素组成
SortedSet tailSet(fromElement):子集,由大于fromElement的元素组成

//: containers/SortedSetDemo.java
// What you can do with a TreeSet.
import java.util.*;
import static net.mindview.util.Print.*;
public class SortedSetDemo {
  public static void main(String[] args) {
    SortedSet<String> sortedSet = new TreeSet<String>();
    Collections.addAll(sortedSet,
      "one two three four five six seven eight"
        .split(" "));
    print(sortedSet);
    String low = sortedSet.first();//最小值
    String high = sortedSet.last();//最大值
    print(low);
    print(high);
    Iterator<String> it = sortedSet.iterator();
    for(int i = 0; i <= 6; i++) {
      if(i == 3) low = it.next();//fromElement
      if(i == 6) high = it.next();//lowElement
      else it.next();
    }
    print(low);
    print(high);
    print(sortedSet.subSet(low, high));//子集1
    print(sortedSet.headSet(high));//子集2
    print(sortedSet.tailSet(low));//子集3
  }
} /* Output:
[eight, five, four, one, seven, six, three, two]
eight
two
one
two
[one, seven, six, three]
[eight, five, four, one, seven, six, three]
[one, seven, six, three, two]
*///:~