Merging two arrayLists into a new arrayList, with no duplicates (Java)

gistfile1.java

// 方法 1

ArrayList al = new ArrayList();
// add elements to al, including duplicates
HashSet hs = new HashSet();
hs.addAll(al);
al.clear();
al.addAll(hs);


// 方法 2

//Add ArrayList1, ArrayList2 and produce a Single arraylist ArrayList3. Now convert it into

Set Unique_set = new HashSet(Arraylist3);



// 方法 3

//Firstly remove duplicates:
arrayList1.remove(arrayList2);

//Then merge two arrayList:
arrayList1.addAll(arrayList2);

//Lastly, sort your arrayList if you wish:
collections.sort(arrayList1);

//In case you don't want to make any changes on the existing list, first create their backup lists:
arrayList1Backup = new ArrayList(arrayList1);