Java set collection and list collection exercises

Title: Add "A", "a", "C", "C", "a", five elements to the set collection first-level list set, and observe if the duplicate value "a" can be successfully added in the list collection first level set set

 PackageCom.hanqi.jihe;ImportJava.util.*; Public classListjihe { Public Static voidMain (string[] args) {ArrayList<String> ls =NewArraylist<string>(); Ls.add (A); Ls.add (A); Ls.add (C); Ls.add (C); if(Ls.add ("a") {System.out.println ("Add Success"); }        Else{System.out.println ("Add Failed"); }         for(String i:ls) {System.out.println (i); }            }}

 PackageCom.hanqi.jihe;ImportJava.util.*; Public classSetjihe { Public Static voidMain (string[] args) {Set<String> SE =NewHashset<string>(); Se.add (A); Se.add (A); Se.add (C); Se.add (C); if(Se.add ("a") {System.out.println ("Add Success"); }        Else{System.out.println ("Add Failed"); }                 for(String i:se) {System.out.println (i); }            }}

Java set collection and list collection exercises