Map concept in JAVA

[Mathan]

Hi,

I am new to JAVA. I have some problem for using map concept.

I am calling getPas method & returning like this.
Map<String,Object> param = getPas(string xyz, String[] Name);
String[] config = (String[]) param.get(Name);

using the Name argument i am fetching the values from Map and casting to String[]. So if the param.get() returns more than one value( like ABC, DEF, KLM, OPQ...) it is working fine. But it return single value( like ABC), it is not storing to config variable, instead throwing error ( type casting error)

Can any one give me the better solution?

Note : i have one more function :
Map<String,Object> param = getPas(string xyz, String[] Name);
String config = (String) param.get(Name);

In this function will not work for String[] means more than one return value( like ABC, DEF, KLM, OPQ...). Thats why i created one new function( the top function)

[Eranga]

What your getPas() do? And what error throw by your code?

[Mathan]

getPas() method will read from local cache. It is throwing Casting Exception. Do you need any more information?

[fishtoprecords]

Make it simpiler until you get it working.
Use the standard get() function, which takes one parameter, the key

Once that works, you can wrap it in other code.

[Mathan]

yes, here the key value is "Name" as already i given the same. Still i am getting problem

[Eranga]

As fishtoprecords says, in simpler way is that working?

[Mathan]

i cannot understand

[daGame]

Quote:

Originally Posted by Mathan

i cannot understand

Test the method using normal Map without using the generics and get it

using the normal get() method. First get this running and then move on to

use generics, generics can get tricky as i've found out, you have to use the

casts properly.

"Use the standard get() function, which takes one parameter, the key" - fishtoprecords

Read the api for maps. It has a function which takes only the key parameter

WTF i cant post any links....this is terrible

[Eranga]

generics cause damages on you for latest versions. So better to move with latest version.

[daGame]

Quote:

Originally Posted by Eranga

generics cause damages on you for latest versions. So better to move with latest version.

Generics are the latest version. Generics are supported from jdk 1.5 onwards

Are we missing something mod?

[Eranga]

Oops, a big mistake. That word should be change.

Quote:

generics cause damages on you for early versions. So better to move with latest version.

Really sorry about my mistake.

[Mathan]

Hi all,

i am getting this exception for above query.
"java.lang.ClassCastException: java.lang.String"

See the code :

String[] configParam = null;

Map<String, Object> paramMap = getNetworkPropertiesFromPas(packageName,
new String[] {parameterName});
if (paramMap != null) {
try{
Set keys = paramMap.keySet(); // The set of keys in the map.
Iterator keyIter = keys.iterator();
while (keyIter.hasNext()) {
String key = (String)keyIter.next(); // Get the next key.
configParam = (String[])paramMap.get(key); // Get the value for that key.

for( int f=0; f < configParam.length; f++ ) {
System.out.println( ".....................Value[" + f + "] is = (" + configParam[f] + ")" );
}
}

}
catch(Exception e){
System.out.println("Exception e is = " + e);
}
}





Here : configParam = (String[])paramMap.get(key);

If the configParam value is more than one value means (like configParam[0]=abc, configParam[1]=def, configParam[2]=ijk) its working fine.
But the value is single means (like configParam[0]=abc) throwing exception like "java.lang.ClassCastException: java.lang.String"


Can any one give me the quick solution?

[fishtoprecords]

Code:

Map<String, Object> paramMap =....
(snip)
configParam = (String[])paramMap.get(key); // Get the value for that key.

You should chante the code to look like

Object oFromMap = paramMap.get(key);
System.out.println(oFromMap.getClass().getName();

so you can see what you are getting. Don't cast blindly.

And if you really are placing an array of String in the map, declare it that way.

Map<String, String[]t> paramMap =....

[Mathan]

Hi,
I tried "Map<String, String[]t> paramMap =...." this...

But i got the below syntax error.
Type mismatch: cannot convert from HashMap<String,Object> to Map<String,String[]>

[sukatoa]

String[] is not absolutely equal to Object.....

[Eranga]

Quote:

Originally Posted by sukatoa

String[] is not absolutely equal to Object.....

Yep, this is what you have going wrong here.

[Mathan]

That is Mr.Fishtoprecords suggestion . so i tried that way also.... not helping. Can any one tell me the good way?

And one thing i can not change to String[] in the Map argument <String, String[]>. because already lot of other functions using only object <String, Object>. So give me better solution ASAP

[fishtoprecords]

I won't give you a solution. I will help.

Did you do the System.out.println that I suggested upthread? What did it tell you? How do you use the information it gave you?

[Mathan]

Yes this is not a solution. thanks for your helping. yes i did System.out. That is not printing anything.

[fishtoprecords]

Didn't print anything? I've never heard of that.
Try changing it to "hello world" and make sure that its getting executed.