Java 集合經常使用方法錦集

Java集合很是的重要，尤爲在業務中，若是你在熟練的使用Java數據結果的集合工做，將會大大的提升工做效率，減小代碼量。

 
1.集合的互換
1.1 Map轉Set
Map<Integer, String> sourceMap = createMap();
Set<String> targetSet = new HashSet<>(sourceMap.values());
1.2 Map轉List
List<Value> list = new ArrayList<Value>(map.values());
1.3 List轉Array
List<String> list = new ArrayList<String>();
list.add("China");
list.add("Switzerland");
list.add("Italy");
list.add("France");
String [] countries = list.toArray(new String[list.size()]);
1.4 Array轉List
String[] countries = {"China", "Switzerland", "Italy", "France"};
List list = Arrays.asList(countries);
1.5 Array轉Set 
String [] countries = {"India", "Switzerland", "Italy"};      
Set<String> set = new HashSet<String>(Arrays.asList(countries));