Creating HashMap, ArrayList and String

[ISAIAH]

Hello,
I need to link two types of ArrayList <String>. I thought to create a HashMap whose key is the first ArrayList <String> and value the ArrayList <String> corespondent.
Here is my code

Public HashMapTest() {
		klst.add("a");
klst.add("b");
klst.add("c");
vallst.add(""+1);
vallst.add(""+2);
vallst.add(""+3);
keyValue.could(klst, vallst);
klst.clear();
vallst.clear();
klst.add("aa");
klst.add(ba);
klst.add("ca");
vallst.add("1a");
vallst.add("2a");
vallst.add("3a");
keyValue.could(klst, vallst);
klst.clear();
vallst.clear();
ArrayList rst = <String>new ArrayList <String>();
ArrayList <String> rsk =new ArrayList <String>();
rsk.add("aa");
rsk.add(ba);
rsk.add("ca");
rst =(ArrayList <String>)keyValue.get(rsk);	
		for(int i =0; I <rst.size(); I + +)
		{
			System.out.System.out.println(rst.get(i));
		}
	}

I review the console error message:

java.lang.NullPointerException

At the line of the loop. Apparently, he does not like me as key to the ArrayList, since I created HashMap <String, ArrayList <String>> without any problems. Yet I have seen no indication cons in the java API. Does someone could tell me why my code does not work, or else tell me another way to combine my two types of ArrayList? Thank you very much in advance.

[Windowed]

Hello,

Note: great care must be Exercised if mutable objects are used as map keys. The Behavior of a map is not specified if the value of an object is changed in a manner that affects equals comparisons while the object is a key in the map.

Brief editable objects should not be used as key, because it breaks the system hash based on the hashCode The hashCode exchange and we can not find the key. Map of the keys should be immutable values. If you need any more help regarding this topic then please feel free to post your queries.

[ISAIAH]

Hello,
Already, I understand why my code does not work. I had not understood this passage this way, for me, the arguments I passed to the HashTable were immutable, since I will not return back to edit, then it is the ArrayList that must remain unchanged. Now, is there anyone how can provide a key with multiple String? I tried to concatenate all String, and find myself with a single string, and it works well, but now my ArrayList of String become too large to be concatenated into one (more than 256 characters).

[GlassFish]

Hello,
I do not know what is the size limit of a String, but can greatly exceed 256 characters, thankfully. Anyway, I'm not sure that a HashMap is tailored to your problem, the ArrayList and related objects are inherently variable (even if we can find immutable), and it's a little malabile use them as keys. Could not you create a class style couple, each instance would combine two <String> ArrayList, and then make you an ArrayList <Couple>? And anyway, once you had your hash ArrayList <String>, how will you assign to the ArrayList in your keys? Anyways if you find may be can you help with class Arrays, Which has many methods to find the hashcode of Tables.

[WinDoWLoCuS]

Hello,
For the data type to use, I do not know, but for the error you had, I just explain it (well I think)
In your code you fill your table and you put in your map:

kls.add("a");
kls.add("b");
kls.add("c");
vallst.add(""+1);
vallst.add(""+2);
vallst.add(""+3);
keyValue.could(kls, vallst);

Just include this in your code and see if the program runs and if there is any error then post back with the error message.

[NetworkeR]

Hello,
Just have a look at the following code. This may help you. I do not know what are your exact needs, but I think this may help you

Public Final class MultiStringKey {
	
	private Final String[] val;
	
	Public MultiStringKey(String ...args) {
		this.val = Args.clone();
		/ / We sort the table
		/ / (Unless the order is important)
		Arrays.fate(this.val);
	}
	
	Public String[] val() {
		return this.val.clone();
	}
	
	@ Override
	Public boolean equals(Object obj) {
		if (obj ==this) return true;
		if (obj instanceof MultiStringKey) {
			return Arrays.equals(this.val, ((MultiString)obj).val);
		}
		return false;
	}
	
	@ Override
	Public int hashCode() {
		return Arrays.hashCode(this.val);
	}
	
	@ Override
	Public String toString() {
		return Arrays.function toString() {
    [native code]
}(this.val);
	}
}