Java 集合常用方法锦集

Java集合非常的重要，尤其在业务中，如果你在熟练的使用Java数据结果的集合工作，将会大大的提高工作效率，减少代码量。

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