Question

Sorry for my poor english, I test the List object with clear method and to assign null value

here is code

public class TestList {
private List<String> list;
private List<List<String>> mainList;

public TestList(){
    list = new ArrayList<String>();
    mainList = new ArrayList<List<String>>();
}
public static void main(String arg[]){
    String[] mylist = {"sunday","monda","tuesday","wednesday","thurday","friday","saturday"};

    TestList tl1 = new TestList();

    for(String s : mylist)
        tl1.list.add(s);


    tl1.mainList.add(tl1.list);

    //tl1.list.clear(); // here if clear then not getting the list

    tl1.list = null; ///// but here to assign null still getting list

    System.out.println("after clear");
    System.out.println();
    for(List<String> list : tl1.mainList){
        for(String s : list){
            System.out.println(s);
        }
    }

}
 }

so my question is when I clear the tl1.list using tl1.list.clear(); and then print the value it’s clear but when I assing null to this tl1.list then it will print the value how?

Answer 1

tl1.list.clear() clears the list list which was added to mainList as well. As Java is object-oriented list and mainList.get(0) reference exactly the same object. If you set tl1.list to null, you only dereference the object, it is still available in mainList.

I’m not sure if I understood your question, but I guess this is what you asked…