即使存在键,Java HashMap也会返回空值(Java HashMap returning null values even when key is present)
我正在开发一个项目,我们在
Map
插入键和值对。如果密钥存在于
Map
,我的代码将返回该密钥的值。但是,即使密钥存在,
HashMap
也不会返回预期值。首先,我从文件中读取键和值对,然后我读取另一个与第一个文件具有几乎相同键的文件。
然后我返回一些键的值,但对于其中许多键,值为
null
。这里是我的代码片段:
Scanner scanner = new Scanner(new FileReader("a.txt")); LinkedHashMap<String, String> map = new LinkedHashMap<String, String>(); while (scanner.hasNextLine()) { String[] columns = scanner.nextLine().split(";"); map.put(columns[0], columns[1]); } System.out.println(map); for (Map.Entry<String, String> entry : map.entrySet()) { // name is the input of second file if (entry.getKey().equals(name)) { num = entry.getValue(); fun(num); } }
我的输入文件是
ABC; 1
DEF; 2
GHI; 3
......而名字将是abc
高清
I am working on a project in which we insert key and value pairs in a
Map
.If the key is present in the
Map
, my code returns the value for that key.However, the
HashMap
is not returning the expected values, even though the key is present.First I read the key and value pairs from a file, then I read another file which has almost the same keys as the first file.
Then I return values for some keys, but for many of them the value is
null
.Here is a snippet of my code:
Scanner scanner = new Scanner(new FileReader("a.txt")); LinkedHashMap<String, String> map = new LinkedHashMap<String, String>(); while (scanner.hasNextLine()) { String[] columns = scanner.nextLine().split(";"); map.put(columns[0], columns[1]); } System.out.println(map); for (Map.Entry<String, String> entry : map.entrySet()) { // name is the input of second file if (entry.getKey().equals(name)) { num = entry.getValue(); fun(num); } }
My input file is
abc;1
def;2
ghi;3
... and name will be abc
def
原文:https://stackoverflow.com/questions/17998097
最满意答案
恕我直言,你应该首先尝试用铅笔和纸解决问题,然后再开始编码。 Mathworld上的这个链接似乎是一个很好的起点。
编辑: 本页上的文章看起来很有希望。
IMHO you should first try to solve the problem with pencil and paper before you start coding. This link at Mathworld seems to be a good starting point.
EDIT: The article on this page looks promising.
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