Array List in collections

[Ale]

I hav a doubt regarding the array lists......
check out the program below....

List l=new ArrayList();
l.add(0,"hell");
l.add(1,"hello");
l.add(2,"hello");
l.add(3,"hello");
l.add(4,"hello");
System.out.println("Index: "+(l.indexOf("hello")));
System.out.println("Index: "+(l.indexOf("hello")));

OUTPUT:index:1
index:1

my doubt is.....evrytime I get the index of the 1st object......what if I want 2 get the index of the duplicate objects other than the 1st and the last objects....??

[JosAH]

I hav a doubt regarding the array lists......
check out the program below....

List l=new ArrayList();
l.add(0,"hell");
l.add(1,"hello");
l.add(2,"hello");
l.add(3,"hello");
l.add(4,"hello");
System.out.println("Index: "+(l.indexOf("hello")));
System.out.println("Index: "+(l.indexOf("hello")));

OUTPUT:index:1
index:1

my doubt is.....evrytime I get the index of the 1st object......what if I want 2 get the index of the duplicate objects other than the 1st and the last objects....??

Yep, unlike the String class Lists don't have two parameter indefOf() method; a
bit inconsistent, but once you've found a first index, you can update an 'offset'
and find the other elements on a sublist of that List and iterate on it again.
There also is a lastIndexOf() method if you need it.

kind regards,

Jos

[Ale]

Yep, unlike the String class Lists don't have two parameter indefOf() method; a
bit inconsistent, but once you've found a first index, you can update an 'offset'
and find the other elements on a sublist of that List and iterate on it again.
There also is a lastIndexOf() method if you need it.

kind regards,

Jos

what if i dot want 2 update the 1st one....but all the other duplicate objects...?

[r035198x]

what if i dot want 2 update the 1st one....but all the other duplicate objects...?

Then you should use a loop to through the ArrayList.

[JosAH]

Then you should use a loop to through the ArrayList.

Loops are soooo Pascalian ;-) Recursion is our friend here:

private void update(List list, Object old, Object subst) {
   int index= list.indexOf(old);
   if (index >= 0) {
      list.set(index, subst);
      update(list.sublist(index+1, list.length());
   }
}
 

kind regards,

Jos ;-)

[r035198x]

Loops are soooo Pascalian ;-) Recursion is our friend here:

private void update(List list, Object old, Object subst) {
   int index= list.indexOf(old);
   if (index >= 0) {
      list.set(index, subst);
      update(list.sublist(index+1, list.length());
   }
}
 

kind regards,

Jos ;-)

Ah, so neat.
And it does cater for the case when old and subst are the same.

[JosAH]

Ah, so neat.
And it does cater for the case when old and subst are the same.

Sure, and a smart compiler can even remove the tail recursion; if it does it
effectively turns the recursive version into an iterative version automagically ;-)

kind regards,

Jos