如何在Java中访问Arraylist中的Dictionary数据？

Question

I am creating Dictionary and an ArrayList such as this.

Dictionary testDict, testDict2 = null;
ArrayList al = new ArrayList();

testDict.put ("key1", dataVar1);
testDict.put ("key2", dataVar2);
testDict2.put ("key1", dataVar1);
testDict2.put ("key2", dataVar2);

al.add(testDict);
al.add(testDict2);

now my issue here is, how can I access the data within the dictionaries? Like for example how would I retrieve key1 from testDict using al?

Many thanks in advance :)

Answer 1

也许这样：

al.get(0).get("key1");

Answer 2

Since testDict is at position 0 (first element of your ArrayList ) you can retrieve it with get(0). .

Example:

Dictionary firstDict = (Dictionary) al.get(0);
Object key1Data = firstDict.get("key1");  

Ps: Generics can greatly improve your code if you are allowed to use it.

Another point is... Why Dictionary and not Map ?

Answer 3

As you can read in the Java Docs all Dictionary objects (note that eg Hashtable is one of them) have a method Object get(Object key) to access it's elements. In your example you could access the value of the entry key1 in textDict like that:

// first access testDict at index 0 in the ArrayList al 
// and then it's element with key "key1"
al.get(0).get("key1");

Note, that you nowhere initialize your Dictionary objects and that the Dictionary class is abstract. So you could for example use a Hashtable (or if you don't need synchronized access use a faster HashMap instead) for your purpose like this:

testDict = new Hashtable<String, String>();

And make sure to use the correct generic types (the second one has to be the type that your dataVar s have)

Answer 4

Not sure why'd you want keep your dictionaries like that, but you can simply loop over your dictionaries.

public Data getData(String key) {
    for(Dictionary dict : al) {
        Data result = dict.get(key);
        if(result != null)
            return result;
        }
    return null;
}