Summary of methods for removing duplicate data from List set in Java

Overview of List Collection

The List collection is a set of ordered elements (each element has a corresponding order index, and the first element has an index of 0) and is repeatable.

Common Methods of List Set

List is a sub-interface of Collection interface, and has all the methods of Collection, as well as some methods of index operation.

void add (int index, E element); Insert element element into index of List collection; boolean addAll(int index, Collection < ? extends E > c); Insert all elements of the collection c into the beginning of index of the collection List; E remove (int index); Removes and returns the element at index; int indexOf (Object o); Returns the index of the first occurrence of the object o in the List collection; int lastIndexOf (Object o); Returns the index of the last occurrence of the object o in the List collection; E set (int index, E element); Replaces the element at the index index with the new element object and returns the replaced old element; E get (int index); Returns the object at the index index of the collection; List < E > subList (int fromIndex, int toIndex); Returns a subset of all elements from index fromIndex (included) to index toIndex (not included); void sort(Comparator < ? super E > c): Sorting List set elements according to Comparator parameters; void replaceAll(UnaryOperator < E > operator): Resets all elements of the collection according to the evaluation rules specified in operator. ListIterator < E > listIterator (); Returns an ListIterator object that inherits the Iterator interface, adding the following methods to the Iterator interface, iterating forward and adding elements: bookean hasPrevious (): Returns whether the set associated with the iterator has the last 1 element; E previous (); Returns 1 element on the iterator; void add (E e); Inserts an element at a specified location;

Java List Weight Removal

1. Loop all elements in list and remove duplicates

public static List removeDuplicate(List list) {  
 for ( int i = 0 ; i < list.size() - 1 ; i ++ ) {  
  for ( int j = list.size() - 1 ; j > i; j -- ) {  
   if (list.get(j).equals(list.get(i))) {  
    list.remove(j);  
   }  
  }  
  }  
 return list;  
}

2. Kick out duplicate elements through HashSet

public static List removeDuplicate(List list) { 
HashSet h = new HashSet(list); 
list.clear(); 
list.addAll(h); 
return list; 
} 

3. Remove duplicate elements from ArrayList, preserving order

//  Delete ArrayList Repeat elements in, keeping order  
 public static void removeDuplicateWithOrder(List list) { 
 Set set = new HashSet(); 
  List newList = new ArrayList(); 
 for (Iterator iter = list.iterator(); iter.hasNext();) { 
   Object element = iter.next(); 
   if (set.add(element)) 
   newList.add(element); 
  } 
  list.clear(); 
  list.addAll(newList); 
 System.out.println( " remove duplicate " + list); 
 } 

4. Traverse the object in list once, use list. contain (), and put it into another list collection if it doesn't exist

public static List removeDuplicate(List list){
		List listTemp = new ArrayList();
		for(int i=0;i<list.size();i++){
			if(!listTemp.contains(list.get(i))){
				listTemp.add(list.get(i));
			}
		}
		return listTemp;
	}

Summarize