CODEWITHSUNDEEP
java
Sanjana Nair
Sanjana Nair

Reputation: 2785

Access Java variable by its name as a String

I have declared 10 ArrayLists with names arraylist1, arraylist2 and so on.

I want to dynamically change variable name in a for loop:

for (int i = 1; i < 5; i++)
{
   arraylist + (i).clear();
   //arraylist1.clear();
   //arraylist2.clear();
   //arraylist3.clear();
   //arraylist4.clear();
   //arraylist5.clear();

}

Is it possible? If so what is format to do so?

Upvotes: 4

Views: 604

Answers (3)

Nick Volynkin
Nick Volynkin

Reputation: 15139

You can not address a variable with its name as string (except with reflection, but that's an overkill for this task).

You can add all these ArrayList's to another List. This is more flexible and, thus, a better option.

List<List<ContactDetails>> lists2 = new ArrayList<List<String>>();
for (int i = 0; i < 10; i++) {
    lists2.add(new ArrayList<ContactDetails>());
}

Or add them to an array and access them by array indexes:

@SuppressWarnings("unchecked")
List<ContactDetails>[] lists = new List[10];
for (int i = 0; i < lists.length; i ++) {
    lists[i] = new ArrayList<ContactDetails>();
}

Now:

for (int i = 1; i < 5; i++)
{
   lists[i].clear();
   lists2.get(i).clear();
}

As both List and array are Iterable, you can use the foreach syntax:

for (List list : lists)
{
   list.clear();
}

for (List list : lists2) {
    list.clear();
}

If you know how to achieve the same with Lambdas / Stream API, please add to the answer.

Upvotes: 8

bhdrkn
bhdrkn

Reputation: 6712

You can also do this with reflection. But I do not recommend it.

public class SoTest {

    @Test
    public void testWithReflection() throws Exception {
        final MyClass myClass = new MyClass();
        for (int i = 0; i < 10; i++) {
            final Field field = myClass.getClass().getDeclaredField("list" + i);
            field.setAccessible(true);
            final List<String> value = (List<String>) field.get(myClass);
            value.clear();
        }
    }

    class MyClass {
        private List<String> list0 = new ArrayList<>();
        private List<String> list1 = new ArrayList<>();
        private List<String> list2 = new ArrayList<>();
        private List<String> list3 = new ArrayList<>();
        private List<String> list4 = new ArrayList<>();
        private List<String> list5 = new ArrayList<>();
        private List<String> list6 = new ArrayList<>();
        private List<String> list7 = new ArrayList<>();
        private List<String> list8 = new ArrayList<>();
        private List<String> list9 = new ArrayList<>();
    }
}

Upvotes: 1

Armand
Armand

Reputation: 24393

If the ArrayLists are class properties, you can achieve this with reflection:

((ArrayList) getClass().getField("arraylist" + i).get(this)).clear();

Upvotes: 1

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