Problems looping over a HashMap<String, String>

Question

I've got a basic HashMap. I'm trying to loop over it and get both the key and the value out of the Map. Here's what I have:

Map<String, String> myMap = versionExtractor.getVersionInfo();
for(String key : myMap.keySet())
    System.out.println(key);
    System.out.println(myMap.get(key));
}

The problem is that this won't compile. There is an error on the line that says System.out.println(myMap.get(key)); that says:

java: class, interface, or enum expected

And the intelliJ IDE says: Cannot resolve symbol 'key'. The perplexing thing is that is resolved key without a problem in the preceding line that says System.out.println(key);. What's up with that?

I've updated my question with the correct code for reading values out of HashMaps. — yeomandev
– yeomandev, Commented Jan 10, 2014 at 17:13
Please don't change your original question, as it now makes all the current answers void. Better to update it, leaving the original there only. — Rohit Jain
– Rohit Jain, Commented Jan 10, 2014 at 17:18
The question hasn't changed, I just fixed a typo in the syntax. The question remains. — yeomandev
– yeomandev, Commented Jan 10, 2014 at 17:19
@quakkels you could add that as an answer and accept that :) — eis
– eis, Commented Jan 10, 2014 at 17:24

Rohit Jain · Accepted Answer · 2014-01-10 17:24:43Z

4

Instead of myMap[key], you should use myMap.get(key). It's a Map, not an array. BTW, if you want both key and value, you can rather iterate over the EntrySet:

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

This saves extra hash calculation, and lookup on every iteration.

As it goes, the issue is something else. The missing { brace after your for statement, makes the closing } of for loop extraneous. Anyways, my original answer was with regards to your original question which used myMap[key] instead.

edited Jan 10, 2014 at 17:24

answered Jan 10, 2014 at 17:11

Rohit Jain

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Comments

Konstantin Yovkov · Accepted Answer · 2014-01-10 17:12:32Z

3

In order to get a corresponding value for a given key, you should use the get(Object key) method:

for(String key : myMap.keySet())
    System.out.println(key);
    System.out.println(myMap.get(key));
}

Even better, in order to iterate a Map, you can use the Map's static Entry class:

for (Map.Entry<String, String> entry: map.entrySet()) {
    System.out.println(entry.getKey());
    System.out.println(entry.getValue());
}

answered Jan 10, 2014 at 17:12

Konstantin Yovkov

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1 Comment

yeomandev Over a year ago

I've updated my question. the problem persists. I cannot use key more than once in the loop.

GriffeyDog · Accepted Answer · 2014-01-10 17:25:11Z

2

You're missing the opening brace on your for statement, so your second println is not part of the for loop.

answered Jan 10, 2014 at 17:25

GriffeyDog

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Comments

Kevin Workman · Accepted Answer · 2014-01-10 17:11:49Z

2

You're treating your Map like an array. That's not how Maps work. Use the Map.get(key) function instead.

For more info, check out the tutorial, which is the first result for googling "java maps".

answered Jan 10, 2014 at 17:11

Kevin Workman

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Comments

Brian Agnew · Accepted Answer · 2014-01-10 17:18:45Z

1

Given that you've got this:

java: class, interface, or enum expected

I wonder if you're compiling with JDK 1.4, and you don't have the enhanced for loop of Java 5 available.

Once you've solved that, don't you want to loop over the Map.Entry objects, to avoid a redudant value lookup via get() ?

for (Map.Entry<String,String> entry : map.entrySet()) {
   ...

edited Jan 10, 2014 at 17:18

answered Jan 10, 2014 at 17:13

Brian Agnew

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2 Comments

yeomandev Over a year ago

I tried that with the same results. the entry will work the first time I use it but not the second.

yeomandev Over a year ago

I'm using 1.7... I found it. I'm missing an opening { after the for() statment. (smack myself in the forehead.)

Sitansu · Accepted Answer · 2014-01-10 17:23:45Z

0

try it :

Map.get(key)

Or

alternative look this example:http://www.mkyong.com/java/how-to-loop-a-map-in-java/

edited Jan 10, 2014 at 17:23

answered Jan 10, 2014 at 17:15

Sitansu

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1 Comment

gowtham Over a year ago

No you cannot , It will look for "key" key in the map and fails.

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