字符串 数组 集合的遍历

数组的遍历：四种方式

int[] arr = new int[] { 11, 2, 44, 1234 };
for (int i : arr) {//增强for循环
            System.out.println(i);
        }

System.out.println("*************************");

for (int i = 0; i < arr.length; i++) {//for循环遍历
            System.out.println(arr[i]);
        }

System.out.println("*************************");

Integer[] arr3 = { 1, 23, 13, 1, 51, 542, 2 };
List<Integer> list2 = Arrays.asList(arr3);//数组转集合然后迭代，但是注意类型不能为基本数据类型
Iterator iterator = list2.iterator();
        while (iterator.hasNext()) {
            Object object = (Object) iterator.next();
            System.out.println(object);
        }

System.out.println("*************************");

String[] arr1 = { "ss", "sss", "xxxx" };
List<String> list = Arrays.asList(arr1);
list.stream().forEach(x -> System.out.println(x));//java8新特性 stream

 字符串遍历：三种方式

        String s = "xxx xxx x xxxxx  xx x xxxx";
        char[] arr2 = s.toCharArray();//字符串转字符数组
        for (char c : arr2) {
            System.out.println(c);
        }
        System.out.println("*************************");
        for (int i = 0; i < arr2.length; i++) {//substring截取加for循环

            System.out.println(s.substring(i, i + 1));
        }
        System.out.println("*************************");
        for (int i = 0; i < arr2.length; i++) {
            System.out.println(s.charAt(i));//charAt获取每一位加for循环

        }

 集合的遍历

public class Test12 {

    public static void main(String[] args) {
        // list的四种遍历方式
        List list = new ArrayList();
        list.add("XXX");
        list.add("FOR");
        list.add("CASH");

        Iterator iterator = list.iterator();// 迭代
        while (iterator.hasNext()) {
            Object object = (Object) iterator.next();
            System.out.println(object);
        }
        for (Object object : list) {// 增强for循环
            System.out.println(object);
        }
        for (int i = 0; i < list.size(); i++) {// for循环
            System.out.println(list.get(i));
        }
        Object[] obj = list.toArray();// 集合转数组，之后参考数组的遍历方式

        // Map的四种遍历方式
        Map<String, Integer> map = new HashMap<String, Integer>();
        map.put("1", 4);
        map.put("2", 1);
        map.put("3", 9);
        Set key = map.keySet();// keySet获取全部key
        Iterator iterator2 = key.iterator();
        while (iterator2.hasNext()) {
            String object = (String) iterator2.next();

            System.out.println(object + " " + map.get(object));
        }
        for (Object object : key) {//增强for循环，遍历key
            System.out.println(object + " " + map.get(object));
        }
        Set<Entry<String, Integer>> entry = map.entrySet();// 获取整个map对象
        Iterator<Entry<String, Integer>> iterator3 = entry.iterator();
        while (iterator3.hasNext()) {
            Map.Entry<String, Integer> entry2 = (Map.Entry<String, Integer>) iterator3.next();
            System.out.println(entry2.getKey() + " " + entry2.getValue());
        }
        for (Entry<String, Integer> entry2 : entry) {//增强for循环，遍历entry对象
            System.out.println(entry2.getKey() + " " + entry2.getValue());
        }
    }

}