CODEWITHSUNDEEP
java
nms
nms

Reputation: 577

ArrayList. Strange things

I have the code:

private class Record {
    byte year;
    float val;
}
Record record=new Record();
List<Record> recList = new ArrayList<Record>();
...
//now I add first element to array list
record.year=12;
record.val=55;
recList.add(record);

//now I add second element to array list
record.year=13;
record.val=77;
recList.add(record);

As you see I add different elements. But as a result all elements in array list are the same. So adding 2-nd, 3-d... element changes all previous elements to the values of last "record". What's wrong? Thanks?

Upvotes: 0

Views: 52

Answers (3)

Pshemo
Pshemo

Reputation: 124215

As you see I add different elements

No, you just edited old Record object and added it again. Each time before you add Record object you need to crate new one.

Upvotes: 1

Jeanne Boyarsky
Jeanne Boyarsky

Reputation: 12266

You need to instantiate new objects so they are physically different objects. Right now, you only have one object that is in the ArrayList multiple times.

Record record = new Record();

Also, you should add hashCode() and equals() to Record since you are working with collections.

Upvotes: 1

Jeroen Vannevel
Jeroen Vannevel

Reputation: 44439

An ArrayList keeps a list of references to objects. You're always modifying the same original object which means the reference is the same, but its values differ.

You can fix it by explicitly assigning a new instance to the record variable:

record.year=12;
record.val=55;
recList.add(record);


record = new Record();
record.year=13;
record.val=77;
recList.add(record);

Upvotes: 3

Related Questions