java 使用Iterator 迭代器遍历AList、Set、Map

1.ArrayList

List list = new ArrayList<Integer>();
list.add(1);
list.add(2);
list.add(3);
// 创建一个迭代器
Iterator iter = list.iterator();
// 循环迭代
while(iter.hasNext()){
    Integer i =(Integer) iter.next();
    System.out.println(i);
}

2.Set集合

Set set = new HashSet<>();
//存储数据
set.add(new Person(1,"张三",20));
set.add(new Person(2,"李四",30));
set.add(new Person(3,"王五",40));

//遍历数据
Iterator iter = set.iterator();
while(iter.hasNext()){
    Person person = (Person)iter.next();
    System.out.println(person.getId() + person.getName() + person.getAge());
}

3.Map集合

Map map = new HashMap<>();
map.put(1, "a");
map.put(2, "b");
map.put(3, "c");

Set set = map.keySet();
System.out.println(set);
Collection col=map.values();
System.out.println(col);

Set<Map.Entry<Integer, String>> entrySet=map.entrySet();
Iterator<Map.Entry<Integer, String>> iter=entrySet.iterator();
while(iter.hasNext()) {
    Map.Entry<Integer, String> entry=iter.next();
    System.out.println("键："+entry.getKey());
    System.out.println("值："+entry.getValue());
}