Which is better ListIterator or Simple list.size() in for loop
Hi everybody
I have one scenario in which, I need to delete the duplicate values from the list (Note : Duplicate values are coming in sequence).
I tried to approaches as follows
1) Using ListIterator
I iterated all values and if I found any duplicate then I called remove() method of Iterator.
2) I made another ArrrayList object, and iterated the old list using size() and for loop, and if I found unique value then I added that value to the new ArrayList.
I also created one test java file to find out the performance in both cases. But I am not pretty sure that this test is correct or not. Please suggest me which approach is correct.
code For Test
publicclass TestReadonly{
publicstaticvoid main(String[] args){
List list =new ArrayList();
long beforeHeap = 0,afterHeap = 0;
long beforeTime = 0,afterTime = 0;
addElementsToList(list);
Collections.sort(list);
callGC();
beforeHeap = Runtime.getRuntime().freeMemory();
beforeTime = System.currentTimeMillis();
System.out.println(" Before "+System.currentTimeMillis()+" List Size "+list.size()+" heap Size "+beforeHeap);
new TestReadonly().deleteDuplicated1(list);
afterHeap = Runtime.getRuntime().freeMemory();
afterTime = System.currentTimeMillis();
System.out.println(" After "+System.currentTimeMillis()+" List Size "+list.size()+" heap Size "+afterHeap);
System.out.println(" Time Differance "+(afterTime-beforeTime)+" Heap Differance "+(afterHeap-beforeHeap));
list.clear();
addElementsToList(list);
Collections.sort(list);
callGC();
beforeHeap = Runtime.getRuntime().freeMemory();
beforeTime = System.currentTimeMillis();
System.out.println(" Before "+System.currentTimeMillis()+" List Size "+list.size()+" heap Size "+beforeHeap);
list =new TestReadonly().deleteDuplicated2(list);
afterHeap = Runtime.getRuntime().freeMemory();
afterTime = System.currentTimeMillis();
System.out.println(" After "+System.currentTimeMillis()+" List Size "+list.size()+" heap Size "+afterHeap);
System.out.println(" Time Differance "+(afterTime-beforeTime)+" Heap Differance "+(afterHeap-beforeHeap));
}
/**
* @param list
*/
privatestaticvoid addElementsToList(List list){
for(int i=0;i<1000000;i++){
list.add("List Object"+i);
}
for(int i=0;i<10000;i++){
list.add("List Object"+i);
}
}
privatestaticvoid callGC(){
Runtime.getRuntime().gc();
Runtime.getRuntime().gc();
Runtime.getRuntime().gc();
Runtime.getRuntime().gc();
Runtime.getRuntime().gc();
}
privatevoid deleteDuplicated1(List employeeList){
String BLANK ="";
String currentEmployeeNumber =null;
String previousEmployeeNumber =null;
ListIterator iterator = employeeList.listIterator();
while (iterator.hasNext()){
previousEmployeeNumber = currentEmployeeNumber;
currentEmployeeNumber = (String) iterator.next();
if ((currentEmployeeNumber.equals(previousEmployeeNumber))
|| ((BLANK.equals(currentEmployeeNumber) && BLANK
.equals(previousEmployeeNumber)))){
iterator.remove();
}
}
}
private List deleteDuplicated2(List employeeList){
String BLANK ="";
String currentEmployeeNumber =null;
String previousEmployeeNumber =null;
List l1 =new ArrayList(employeeList.size());
for (int i =0;i<employeeList.size();i++){
previousEmployeeNumber = currentEmployeeNumber;
currentEmployeeNumber = (String) employeeList.get(i);
if (!(currentEmployeeNumber.equals(previousEmployeeNumber))
|| ((BLANK.equals(currentEmployeeNumber) && BLANK
.equals(previousEmployeeNumber)))){
l1.add(currentEmployeeNumber);
}
}
return l1;
}
}
Output
Before 1179384331873 List Size 1010000 heap Size 60739664
After 1179384365545 List Size 1000000 heap Size 60737600
Time Differance 33672 Heap Differance -2064
Before 1179384367545 List Size 1010000 heap Size 60739584
After 1179384367639 List Size 1000000 heap Size 56697504
Time Differance 94 Heap Differance -4042080>
