更新时间:2022-09-29 21:07:51
ArrayList<String> c = new ArrayList<String>();
c.add("hello");
c.add("world");
String a = new String("aya");
c.add(a);
for( Object obj : c )
{
System.out.println( (String)obj );
}
c.set(2, "111");
Iterator<String> it = c.iterator();
while(it.hasNext())
{
System.out.println( (String)it.next() );
}
ArrayList 的迭代器还有 ListIterator 可以有正反两种查询,先hasNext知道最后 hasPrevious才能有值
[java] view plaincopy
ListIterator<String> it2 = c.listIterator();
while(it2.hasNext())
{
System.out.println( "hasNext " + (String)it2.next() );
}
while(it2.hasPrevious())
{
System.out.println( "hasPrevious " + (String)it2.previous() );
}
|
TreeSet<Integer> nums = new TreeSet<Integer>();
nums.add(4);
nums.add(3);
nums.add(2);
nums.add(1);
System.out.println(nums); //整个集合
System.out.println(nums.first());
System.out.println(nums.last());
System.out.println(nums.headSet(3)); //小于3,但不包括3
System.out.println(nums.tailSet(3)); //大于等于3
System.out.println(nums.subSet(1, 3)); 大于等于1,小于3
|
enum Season
{
SPRING,SUMMER,FALL,WINTER;
}
public class Main {
public static void main(String[] args) {
EnumSet es1 = EnumSet.allOf(Season.class); //创建一个EnumSet集合,集合元素就是Season枚举类的全部枚举值
System.out.println(es1);
EnumSet es2 = EnumSet.noneOf(Season.class); //空集合,但指定其中的元素是Season类的枚举值
System.out.println(es2);
es2.add(Season.SPRING);
es2.add(Season.SUMMER);
System.out.println(es2);
EnumSet es3 = EnumSet.of(Season.SPRING, Season.SUMMER); // 以指定枚举值创建EnumSet
System.out.println(es3);
EnumSet es4 = EnumSet.range(Season.SPRING, Season.FALL); // 范围值
System.out.println(es4);
EnumSet es5 = EnumSet.complementOf(es4); //Season中 除去es4里剩下的部分 为es5
System.out.println(es5);
}
}
|
LinkedList<String> books = new LinkedList<String>();
books.offer("test1"); //加入队列尾部
books.push("test2"); //入栈
books.offerFirst("test3"); //放入头部
for(int i=0; i<books.size(); i++)
{
System.out.println( books.get(i) );
}
System.out.println( books.peekFirst() ); //访问不删除
System.out.println( "log1: " + books );
System.out.println( books.pollFirst() ); //访问并删除
System.out.println( "log2: " + books );
|
enum Season
{
SPRING,SUMMER,FALL,WINTER;
}
public class Main {
public static void main(String[] args) {
HashMap<Integer, String> map1 = new HashMap<Integer, String>();
map1.put(1, "hello");
map1.put(2, "world");
System.out.println(map1);
System.out.println(map1.containsKey(3));
System.out.println(map1.containsValue("world"));
map1.put(2, "aya");
System.out.println(map1);
for(Map.Entry<Integer, String> m : map1.entrySet())
{
System.out.println(m);
System.out.println(m.getKey());
}
EnumMap map2 = new EnumMap(Season.class);
map2.put(Season.SPRING, "spring");
map2.put(Season.SUMMER, "summer");
System.out.println(map2);
}
}
|