asked on

removing members from an ArrayList

i am adding an object "pnew" to a queue (which i am implementing as an arrayList--same thing right?) after I add it i need to back up a step so I have a "remove" method which takes off the last element in "pnew". The problem is that when I remove the member from "pnew", it also removes it from the queue. The queue is an ArrayList of paths, pnew is an ArrayList of integers

path pnew = new path(start);
ArrayList<path> queue = new ArrayList<path>();

queue.add(pnew);
pnew.remove();

Mayank S

>> which i am implementing as an arrayList--same thing right

You mean the ArrayList implements a queue? It can....

Though it looks like you have:

/* Queue --> */ path pnew = new path(start);
/* ArrayList --> */ ArrayList<path> queue = new ArrayList<path>(); // also named as 'queue' ?

>> pnew.remove();

We need to know what is the implementation of the path class and what it does.

jpking72

ASKER

====================================================

int source = this.findNode(a);
int sink = this.findNode(b);
curr.add(source);
path p = new path(curr);
queue.add(p);

for (int row = 0; row < nodes.length; row++) {
path pnew = queue.remove(0);
for (int col = 0; col < nodes.length; col++) {
if (matrixCap[row][col] != 0) {
pnew.add(col);
if (pnew.contains(sink))
System.out.println(queue.toString());
queue.add(pnew);
pnew.remove();
}
}

}
========================================
class path
========================================
public class path {

private ArrayList<Integer> in = new ArrayList<Integer>();

/** Creates a new instance of path */
public path(ArrayList<Integer> i) {

for (int j = 0; j < i.size(); j ++) {
in.add(j, i.get(j));
}

}

public ArrayList<Integer> add(Integer i) {

in.add(i);
return in;
}

public ArrayList<Integer> remove() {

if (in.size() >0){
in.remove(in.size()-1);
return in;}

else return in;

}

public boolean contains(int sink) {
for (int i = 0; i < in.size(); i++) {
if (in.get(i).equals(sink))
return true;
}
return false;
}

public String toString() {
StringBuilder out = new StringBuilder();
out.append("found path: ");

for (int i = 0; i < in.size(); i++) {
out.append(in.get(i));
out.append(" ");
}
return out.toString();

}
}

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Mayank S

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jpking72

ASKER

i don't understand...i rewrote the code and still the same problem:
when I update current[i], queue also changes the previous entry in the ArrayList. I want it to add another distinct array to the end of the ArrayList every time.

ArrayList<int[]> queue = new ArrayList<int[]>();
int[] current = new int[10];

for (col = 0; col<nodes.length; col++) {
current[i] = col;
queue.add(current)
}

jpking72

ASKER

hello?

Mayank S

If path holds Integers, maybe even the array list should be of Integers

ArrayList <Integer> queue = new ArrayList <Integer> () ;

>> hello?

Be patient - I come here in my free time and our time zones could also be different. Any reason for the C grade?