Java集合学习简单demo整理

public class Demo {
    public static void main(String[] args){
        List<Integer> list = new ArrayList<Integer>();
        list.add(1);
        list.add(2);
        if (list.contains(2)){
            System.out.println("ok");
        }

        Collection<Integer> days = new ArrayList<Integer>();
        for (int i=0;i<10;i++){
            days.add(i);
        }
        System.out.println(days);
        Iterator iterator = days.iterator();
        while (iterator.hasNext()){
            System.out.println(iterator.next());
        }

        List<String> stringList = Arrays.asList("java","go","rust","kotlin");
        Iterator iterator1 = stringList.iterator();
        while (iterator1.hasNext()){
            System.out.println(iterator1.next());
        }

        String[] arr1 = {"java","go"};
        String[] arr2 = Arrays.copyOf(arr1,4);
        for (String str:arr2) {
            System.out.println(str);
        }

        Map<String,String> map = new HashMap();
        map.put("aa","11");
        map.put("bb","22");
        System.out.println(map.keySet());
        System.out.println(map.entrySet());
        Set<String> set = new HashSet<String>();
        set.add("aa");
        set.add("bb");
        System.out.println(set);
    }
}