如何从Java ArrayList对象转换为实际值

Question

I'm trying to get a value from the databae.

My Database query:

String GroupID1="select idCompanies from companies where Company_Name='ACME';";

here I'm calling to a javabeans which give back an ArrayLIst with one element

ArrayList<?> IdGroup1=oper.getList(GroupID1);

then, I print the result:

System.out.println(IdGroup1);

The query works fine, however I'm getting as a result:

[javabeans.ListOneElement@609f6e68]

Instead of the real value. How can I convert the java object to the real value?

Answer 1

您正在打印ArrayList对象IdGroup1 ，您需要进行迭代以获取alues

Answer 2

This code will retrieve the first (and only) item from the list:

System.out.println(IdGroup1.get(0).toString());

Adding the following will prevent a nullPointerException:

if (!IdGroup1.isEmpty())
    System.out.println(IdGroup1.get(0).toString());

-Added .toString() to get the value of the object

Answer 3

Consider what type of Object oper.getList(GroupID1) will return.

You need to accommodate for whatever object that is and then convert it to String.

You need to:

1. Unpackage your list (that is a list contains, and is expected by java to possibly contain multiple objects, so it doesn't automatically 'unpack' it for you if you have a list of 1 object)

2. Extract your string. Here java might cleverly convert a number (int, float, etc. ) to a string for you.

For part two, look at what you expect the object to be by finding the JavaDocs for whatever package is handling your database queries. Then see how to extract your string.

It might be as simple as System.out.println(IdGroup1.get(0).toString());
Where get(0) unpackages the object from the list, and toString() extracts the string.

If you still get back javabeans.ListOneElement@41ccdc4d try other methods to extract your string.... toValue() perhaps? It depends on the packages you're using.