迭代Map中的键和值

Question

Sometimes I find myself duplicating code to extract both key and value entries from a Map (when testing/debugging a third-party API, for example).

Map<String, String> someMap;
Set<String> keys = someMap.keySet();
for(int j=0;j<someMap.size();j++){
    String key = (String) keys.toArray()[j];
    System.out.println("key > " + key + "  : value = " + someMap.get(key));
}

I know Groovy has some great abstractions for this (eg Get key in groovy maps ), but I'm constrained to POJ. Surely there must be a more elegant and less verbose way to do this, in Java I mean?

Answer 1

You can use Entry<String,String> and iterate over it with a for-each loop . You get the Entry object by using Map.entrySet() .

The key and value from an entry can be extracted using Entry.getKey() and Entry.getValue()

Code example:

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

Answer 2

You can simplify the code by using the for each loop:

Map<String, String> someMap;
for(String key : someMap.keySet()){
    System.out.println("key > " + key + "  : value = " + someMap.get(key));
}

Or you do this with the entry set. Amit provided some code for that while I was still editing my answer ;-)

Answer 3

Depending on what you're trying to do, Google collections has a Maps API that provides some helper functions to transform maps etc.

If you're looking to just pretty print the map, this post may be useful