JAVA菜鸟入门(18) Set的Iterator

1. 使用iterator遍历Set中元素

public class SetIteratorDemo {
public static void main(String[] args) {
HashSet<String> objectSet = new HashSet<String>();
objectSet.add("white");
objectSet.add("white");
objectSet.add("green");
objectSet.add("yellow");
objectSet.add("blue");
objectSet.add("Yellow");
objectSet.add("red");
objectSet.add("white");
System.out.println("1 --------------------");
for (String item : objectSet) {
System.out.println(item);
}
System.out.println("2 --------------------");
Iterator it = objectSet.iterator();
while (it.hasNext()) {
System.out.println(it.next());
}
}
}

output:

1 --------------------
red
blue
green
Yellow
white
yellow
2 --------------------
red
blue
green
Yellow
white
yellow

2. 使用Iterator 删除Set中元素

public class SetIteratorRemoveDemo {
public static void main (String [] args) {
// Set<Integer> numberSet = new HashSet<Integer>(); //works fine
//Set numberSet = new HashSet(); //works fine
HashSet numberSet = new HashSet(); //works fine
for (int i = 0; i < 10; ++i) {
numberSet.add(new Integer(i));
}

for (Iterator<Integer> it = numberSet.iterator(); it.hasNext(); ) {
Integer a = it.next();
if (a % 2 == 0) {
it.remove(); // this actually differs from my habit.
}
}
System.out.println(numberSet.toString());
}
}

output:

[1, 3, 5, 7, 9]

3. 

Set interface permits "null key" , so do HashSet, LinkedHashSet, TreeSet.