Map 遍历方式

map集合的遍历方式，以HashMap为例。

Map<String, String> map = new HashMap<>();
map.put("k1", "v1");
map.put("k2", "v2");

entrySet

// 增强 for 循环
for (Map.Entry<String, String> entry : map.entrySet()) {
    System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
}

// 迭代器
Iterator<Map.Entry<String, String>> iterator = map.entrySet().iterator();
while (iterator.hasNext()) {
  Map.Entry<String, String> entry = iterator.next();
  System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
}

keySet

for (String key : map.keySet()) {
    System.out.println("Key = " + key + ", Value = " + map.get(key));
}

Java 8的forEach和Lambda表达式

map.forEach((key, value) -> System.out.println("Key = " + key + ", Value = " + value));

values 只取value值

Collection<String> values = map.values();
for (int i = 0; i < values.size(); i++) {
    System.out.println("Value = " + values.toArray()[i]);
}
for (String value : values) {
    System.out.println("Value = " + value);
}