Retrieving hashmap values in java

问题

I wrote below code to retrieve values in hashmap. But it didnt work.

HashMap<String, String> facilities = new HashMap<String, String>();

Iterator i = facilities.entrySet().iterator();

while(i.hasNext())
{
    String key = i.next().toString();  
    String value = i.next().toString();
    System.out.println(key + " " + value);
}

I modified the code to include SET class and it worked fine.

Set s= facilities.entrySet();
Iterator it = facilities.entrySet().iterator();
while(it.hasNext())
{
    System.out.println(it.next());
}

Can anyone guide me what went wrong in above code without SET class??

P.S - I do not have much programming exp and started using java recently

回答1:

You are calling next() two times.

Try this instead:

while(i.hasNext())
{
    Entry e = i.next();
    String key = e.getKey();  
    String value = e.getValue();
    System.out.println(key + " " + value);
}

In short you could also use the following code (which also keeps the type information). Using Iterator is pre-Java-1.5 style somehow.

for(Entry<String, String> entry : facilities.entrySet()) {
    String key = entry.getKey();
    String value = entry.getValue();
    System.out.println(key + " " + value);
}

回答2:

The problem is you're calling i.next() to get the key, then you call it again to get the value (the value of the next entry).

Another problem is you use toString on the one of the Entry's, which is not the same as getKey or getValue.

You need to do something like:

Iterator<Entry<String, String>> i = facilities.entrySet().iterator();
...
while (...)
{
   Entry<String, String> entry = i.next();
   String key = entry.getKey();  
   String value = entry.getValue();
   ...
}

回答3:

Iterator i = facilities.keySet().iterator();

while(i.hasNext())
{
    String key = i.next().toString();  
    String value = facilities.get(key);
    System.out.println(key + " " + value);
}

回答4:

You're calling i.next() more than once in the loop. I think this is causing the trouble.

You can try this:

HashMap<String, String> facilities = new HashMap<String, String>();
Iterator<Map.Entry<String, String>> i = facilities.entrySet().iterator();
Map.Entry<String, String> entry = null;
while (i.hasNext()) {
    entry = i.next();
    String key = entry.getKey();
    String value = entry.getValue();
    System.out.println(key + " " + value);
}

回答5:

String key;
for(final Iterator iterator = facilities.keySet().iterator(); iterator.hasNext(); ) {<BR>
   key = iterator.next();<BR>
   System.out.println(key + " : " + facilities.get(key));<BR>

for (Entry<String, String> entry : facilities.entrySet()) {<BR>
System.out.println(entry.getKey() + " : " + entry.getValue();<BR>
}

来源：https://stackoverflow.com/questions/15022149/retrieving-hashmap-values-in-java

标签

java

hashmap