Adding element to list deletes previous elements

Question

i have a class with a constructor that returns objects. I'm adding these objects to a list but having trouble because every time i add a new element it replaces the previous ones with the current element that i am adding.

Here is the list and output:

    Objects a = new Objects("test1");
    Objects b = new Objects("test2");

    List<Objects> c = new ArrayList();

    c.add(a);
    c.add(b);
    System.out.println(c.get(0).getTest());
    System.out.println(c.get(1).getTest());

Here is the output:

test2
test2

Here is the class creating/returning the objects:

public class Objects
{
    public static String test;

    public Objects (String test)
    {
        this.test = test;
    }

      public String getTest()
      {
          return test;
      }
}

provide the full source file you are using, given the error it is relevant to show it in extenso. — benzonico, Dec 11 '15 at 14:06
FYI it doesn't delete it. If it did your output would have be just test2 once. Attention to detail ! — StackFlowed, Dec 11 '15 at 14:11
Thank you, i got rid of the static type on the test variable and its working now. — HashTables, Dec 11 '15 at 14:14
Remove static from here. public static String test; use without static public String test; — A J, Dec 11 '15 at 14:19

score 2 · Answer 1 · answered Dec 11 '15 at 14:08

remove the static in Objects for class member test:

public class Objects
{
    public String test;

    public Objects (String test)
    {
        this.test = test;
    }

      public String getTest()
      {
          return test;
      }
}

then you will get the desired output:

Test1

Test2

Sometimes, you want to have variables that are common to all objects. This is accomplished with the static modifier. Fields that have the static modifier in their declaration are called static fields or class variables. They are associated with the class, rather than with any object.

score 1 · Accepted Answer · answered Dec 11 '15 at 14:11

1

Static is the problem here. Remove Static and it will work fine. Using statics like this example is not a good practice, read here.

answered Dec 11 '15 at 14:11

Darshan Mehta

30,102
11
68
102

score 0 · Answer 3 · edited May 23 '17 at 10:27

Change public static String test; as public String test;

The static keyword in Java means that the variable or function is shared between all instances of that class as it belongs to the type, not the actual objects themselves.

So if you have a variable: private static int i = 0; and you increment it (i++) in one instance, the change will be reflected in all instances. i will now be 1 in all instances.

And Read

score 0 · Answer 4 · answered Dec 11 '15 at 14:10

public static String test;

This is the problem. test is class level variable, so you simply modify it, instead of creating a new one. Also, usually you make the variable private, and provide getter and setter to for the variable. That is called encapsulation

score 0 · Answer 5 · answered Dec 11 '15 at 14:11

0

Since you have declared test as static same variable will be used for all Objects instances. So its not overwriting the objects in the list . Its overwriting the value of test.

Solution :

Remove static modifier public String test;

answered Dec 11 '15 at 14:11

Rahman

3,755
3
26
43

Adding element to list deletes previous elements

5 Answers5