Map的5種遍歷方式
Map<String, String> map = new HashMap<String, String>();
map.put("bors", "博士");
map.put("bear2", "熊二");
1.entrySet遍歷(牆裂推薦!!!)
for (Map.Entry<String, String> entry : map.entrySet()) {
String k = entry.getKey();
String v = entry.getValue();
System.out.println(k + " : " + v);
}
2.在for循環中遍歷key或者value,一般適用於只需要map中的key或者value時使用,在性能上比使用entrySet較好
//key
for (String key : map.keySet()) {
System.out.println(key);
}
//value
for (String value : map.values()) {
System.out.println(value);
}
3.通過Iterator遍歷
Iterator<Map.Entry<String, String>> entries = map.entrySet().iterator();
while (entries.hasNext()) {
Map.Entry<String, String> entry = entries.next();
String key = entry.getKey();
String value = entry.getValue();
System.out.println(key + " : " + value);
}
4.通過鍵找值遍歷,這種方式的效率比較低,因為本身從鍵取值是耗時的操作
for (String key : map.keySet()) {
String value = map.get(key);
System.out.println(key + " : " + value);
}
5.java8 Lambda, 性能低於entrySet,所以更推薦用entrySet的方式
map.forEach((k, v) -> { System.out.println(k + " : " + v); });