java项目中如何实现集合的相互转换

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()]); 

String[] countries = {"China", "Switzerland", "Italy", "France"}; 
List list = Arrays.asList(countries); 

List<Value> list = new ArrayList<Value>(map.values()); 

String [] countries = {"India", "Switzerland", "Italy"};    
Set<String> set = new HashSet<String>(Arrays.asList(countries)); 
System.out.println(set); 

Map<Integer, String> sourceMap = createMap(); 
Set<String> targetSet = new HashSet<>(sourceMap.values());