two arraylists, same value but not the same reference

dwang040

FYI this is java

I can't find anything online so I was hoping you guys could help me out. So, i have an arraylist of values (ex: 3,2,5,5,2) and a temp arraylist with the same value (3,2,5,5,2) however, this temp array is not referencing the same thing as arraylist. So, if i do collections.sort(temp arraylist), it then get (2,2,3,5,5). I know want to delete the 5's. so if the arraylist has a 5 in it, it's removed. so now, arraylist is (3,2,2). Now, i want temp arraylist to get the same values from arraylist, but i want to sort temp arraylist and leave arraylist alone. How can i do that? since the only way that i know to make two arraylists similar is temp arraylist = arraylist, but then they reference the same thing so when i sort temp arraylist, arraylist is also sorted. Any ideas? thanks.

quark

If you have two array lists a1 and a2 then to make a1 hold the same vales as a2 then

a1.clear();
a1.addAll(a2);

If I have got the right syntax

dwang040

Okay, so just to double check, of I sort a1, a1 will be sorted while a2 will not.

GoToLoop

For ArrayList, we can use its method clone() in order to get a new 1 w/ same content:
http://docs.Oracle.com/javase/8/docs/api/java/util/ArrayList.html#clone--

Then we can use Collections.sort() or any other mutable methods on it w/o modifying the original : :D
http://docs.Oracle.com/javase/8/docs/api/java/util/Collections.html#sort-java.util.List-

// forum.Processing.org/two/discussion/16803/
// two-arraylists-same-value-but-not-the-same-reference

// GoToLoop (2016-May24)

final int QTY = 10, RANGE = 100;

ArrayList<Integer> nums = new ArrayList<Integer>(QTY);
for (int i = 0; i++ < QTY; nums.add((int) random(RANGE)));

ArrayList<Integer> sortedNums = (ArrayList<Integer>) nums.clone();
java.util.Collections.sort(sortedNums);

println("original:", nums);
println("cloned:  ", sortedNums);

exit();

GoToLoop

Given that you're storing whole numerical values in your ArrayList<Integer> container; how about IntList instead? ;;) https://Processing.org/reference/IntList.html

We can use its values() or array() methods in order to get an int[] array.
Then pass it as argument for another new IntList as a means to attain the same result as ArrayList's clone(): O:-)

BtW, IntList got its own sort() & sortReverse() methods builtin: \m/

1. https://Processing.org/reference/IntList_sort_.html
2. https://Processing.org/reference/IntList_sortReverse_.html

// forum.Processing.org/two/discussion/16803/
// two-arraylists-same-value-but-not-the-same-reference

// GoToLoop (2016-May24)

final int QTY = 10, RANGE = 100;

IntList nums = new IntList(QTY);
for (int i = 0; i++ < QTY; nums.append((int) random(RANGE)));

IntList sortedNums = new IntList(nums.values());
sortedNums.sort();

println("original:", nums);
println("cloned:  ", sortedNums);

exit();

dwang040

Cool, thanks. I never learned int list (my high school isn't big in programming, so the hardest thing we've probably coded is an arraylist)

GoToLoop

@dwang040, just now realized that ArrayList got an overloaded constructor which accepts any Collection as its argument: 3:-O
http://docs.Oracle.com/javase/8/docs/api/java/util/ArrayList.html#ArrayList-java.util.Collection-

Therefore now, rather than relying on its clone() method: sortedNums = (ArrayList<Integer>) nums.clone();
We can simply instantiate another ArrayList passing the original Collection to it:
sortedNums = new ArrayList<Integer>(nums);

// forum.Processing.org/two/discussion/16803/
// two-arraylists-same-value-but-not-the-same-reference

// GoToLoop (2016-May24)

import java.util.Collections;
import java.util.List;

final int QTY = 10, RANGE = 100;

List<Integer> nums = new ArrayList<Integer>(QTY);
for (int i = 0; i++ < QTY; nums.add((int) random(RANGE)));

List<Integer> sortedNums = new ArrayList<Integer>(nums);
Collections.sort(sortedNums);

println("original:", nums);
println("cloned:  ", sortedNums);

exit();

GoToLoop

Although we can shallow-clone any Collection by creating another 1 and passing the original 1 as its argument; if the variable which is tasked to hold the cloned Collection happens to be final, we can't assign the newly-created clone to it! :-SS

import java.util.List;

// Both nums & sortedNums variables are sealed against
// later reassignments via final keyword:
final int QTY = 10, RANGE = 100;
final List<Integer> nums = new ArrayList<Integer>(QTY);
final List<Integer> sortedNums = new ArrayList<Integer>(QTY);

// Compilation Error: sortedNums is final!
sortedNums = new ArrayList<Integer>(nums);

In this case, we're obliged to rely on clear() + addAll() as @quark advised: L-)

1. http://docs.oracle.com/javase/8/docs/api/java/util/Collection.html#clear--
2. http://docs.oracle.com/javase/8/docs/api/java/util/Collection.html#addAll-java.util.Collection-

I advocate a lot about declaring variables w/ final as much as possible.
Recycling an object by re-using it rather than creating another 1 is much more "ecological": O:-)

// forum.Processing.org/two/discussion/16803/
// two-arraylists-same-value-but-not-the-same-reference

// GoToLoop (2016-May24)

import java.util.Collections;
import java.util.List;

// Both nums & sortedNums variables are sealed via final keyword:
final int QTY = 10, RANGE = 100;
final List<Integer> nums = new ArrayList<Integer>(QTY);
final List<Integer> sortedNums = new ArrayList<Integer>(QTY);

for (int i = 0; i++ < QTY; nums.add((int) random(RANGE)));

// Compilation Error: sortedNums is final!
//sortedNums = new ArrayList<Integer>(nums);

sortedNums.clear(); // Assuming sortedNums is perhaps already holding elements.
sortedNums.addAll(nums);
Collections.sort(sortedNums);

println("original:", nums);
println("cloned:  ", sortedNums);

exit();

dwang040

Okay, thanks for the update!

GoToLoop

1 more final update. This time for how to do the same for final IntList: :P

// forum.Processing.org/two/discussion/16803/
// two-arraylists-same-value-but-not-the-same-reference

// GoToLoop (2016-May24)

// Both nums & sortedNums variables are sealed via final keyword:
final int QTY = 10, RANGE = 100;
final IntList nums = new IntList(QTY), sortedNums = new IntList(QTY);

for (int i = 0; i++ < QTY; nums.append((int) random(RANGE)));

// Compilation Error: sortedNums is final!
//sortedNums = new IntList(nums.values());

sortedNums.clear(); // Assuming sortedNums is perhaps already holding elements.
sortedNums.append(nums);
sortedNums.sort();

println("original:", nums);
println("cloned:  ", sortedNums);

exit();

dwang040

Great! Thanks for the help!