Does Java pass by reference or pass by value?

How to find out duplicates in a List

List objStringList = new ArrayList();
objStringList.add("a");
objStringList.add("b");
objStringList.add("c");
objStringList.add("d");
objStringList।add("c");

Approach - I
Iterator objIterator = objStringList.iterator();
while(objIterator.hasNext()) {
String value = objIterator.next();
if(objStringList.indexOf(value) != objStringList.lastIndexOf(value)) {
System.out.println("\n Duplicates detected: " + value);
}
}

for(String objString: objStringList) {
if(objStringList.indexOf(objString) != objStringList.lastIndexOf(objString)) {
System.out.println("\n Duplicates detected: " + objString);
}
}

Approach - II

Set objStringSet = new HashSet();
for(String objString: objStringList) {
boolean result = objStringSet.add(objString);
if (result == false) {
System.out.println("\n Duplicates detected: " + objString);
}
}

Approach - III

List list = new ArrayList();
Set set = new HashSet();
list.add("1");
list.add("2");
list.add("3");
list.add("4");
list.add("5");
set.addAll(list);
if(set.size() < list.size()) {
System.out.println("list has duplicates");
}