how to declare ArrayList of ArrayList in java

Question

I want to declare an ArrayList within another ArrayList.

I declared ArrayList of ArrayList and added the elements in the following manner successfully but at the time of retrieval its showing class cast exception.

List<List<UnderDefinedFunction> parentAL=new ArrayList<List<UserDefinedFunction>>();
List<UserdefinedFunction> childAL=new ArrayList<UserDefined>();

childAL.add(userdefinedfunction);
...............
..............
parentAL.add(childAL);

At the time of retrieval it is showing class cast exception.

for(int i=0;i<parentAL.size();i++){
    List<UserDefinedFunction> al=parentAL.get(i);
}

I tried with following code also:

ArrayList<ArrayList<UserDefinedfunction> al=new ArrayList<ArrayList<UserDefinedFunction>>();

but I am getting same problem.

Why is it showing any error any mistake is done any idea ???

kai · Accepted Answer · 2014-02-07 14:03:26Z

4

Do:

 List<ArrayList<UnderDefinedFunction>> parentAL=new ArrayList<ArrayList<UserDefinedFunction>>();

instead and it will work.

answered Feb 7, 2014 at 14:03

kai

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2 Comments

user1990992 Over a year ago

i am getting same error can you please provide the code for retrieval @Kai

kai Over a year ago

i tested that code you pasted here. for me it works fine. the problem is at another point in your code. pls post the stacktrace and maybee more code. and the way you retrieval the list is correct too.

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