Map和List的遍历

List的三种遍历方式：
public class TestList {

public static void main(String[] args) {
    List<String> list = new ArrayList<>();
    list.add("孙悟空");
    list.add("唐三藏");
    list.add("猪八戒");
    list.add("沙悟净");
    String listString = list.toString();
    System.out.println(listString);

    Integer size = list.size();
    for (int i = 0; i < size; i++) {
        String value1 = list.get(i);
        System.out.println(value1);
    }
    System.out.println("==========================");

    Iterator<String> iterator = list.iterator();
    while (iterator.hasNext()) {
        String value2 = iterator.next();
        System.out.println(value2);
    }
    System.out.println("==========================");
    

    for (String string : list) {
        System.out.println(string);
    }
}}

// 第一种方式遍历list集合：for循环
Integer size = list.size();
for (int i = 0; i < size; i++) {
String value1 = list.get(i);
System.out.println(value1);
}
// 第二种方式遍历list集合：iterator 迭代器
Iterator<String> iterator = list.iterator();
while (iterator.hasNext()) {
String value2 = iterator.next();
System.out.println(value2);
}
// 第三种方式遍历list集合：foreach
for (String string : list) {
System.out.println(string);
}

Map的三种遍历方式：

public static void main(String[] args) {
    Map<String, Integer> map = new HashMap<>();
    map.put("孙悟空", 1);
    map.put("唐三藏", 2);
    map.put("猪八戒", 3);
    map.put("沙悟净", 4);

    Set<String> keySet = map.keySet();
    for (String key : keySet) {
        Integer value = map.get(key);
        System.out.println("键："+ key + "值："+ value);
    }

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

// map遍历操作的第一种方法：keyset + foreach
// 采用keyset方法通过key值获取value值---》效率低
Set<String> keySet = map.keySet();
for (String key : keySet) {
Integer value = map.get(key);
System.out.println("键："+ key + "值："+ value);
}

// map遍历操作的第二种方式：map.entrySet();+foreach 方法进行遍历
Set<Entry<String, Integer>> set = map.entrySet();
for (Entry<String, Integer> entry : set) {
String key = entry.getKey();
Integer value = entry.getValue();
System.out.println("键："+ key + "值"+value);
}

// map遍历操作的第三种方式：map.entrySet() +迭代器
Iterator<Entry<String, Integer>> entrySet = map.entrySet().iterator();
while (entrySet.hasNext()) {
Entry<String, Integer> entry = entrySet.next();
String key = entry.getKey();
Integer value = entry.getValue();
System.out.println("键：" + key + " " + "值：" + value);
}
}
所有的方法都是卸载main方法之中的。