【转】Java集合间的相互转换

public class TestApp {

public static void main(String[] args) {
//List-->数组
List<String> list = new ArrayList<String>();
list.add("蹇伟");
list.add("Jerval");
list.add("杰威");
Object[] objects = list.toArray();//返回Object数组
System.out.println("objects:"+Arrays.toString(objects));
String[] strings1 = new String[list.size()];
list.toArray(strings1);//将转化后的数组放入已经创建好的对象中
System.out.println("strings1:"+Arrays.toString(strings1));
String[] strings2 = list.toArray(new String[0]);//将转化后的数组赋给新对象
System.out.println("strings2:"+Arrays.toString(strings2));
//数组-->List
String[] ss = {"JJ","KK"};
List<String> list1 = Arrays.asList(ss);
List<String> list2 = Arrays.asList("AAA","BBB");
System.out.println(list1);
System.out.println(list2);
//List-->Set
List<String> list3 = new ArrayList<String>(new HashSet<String>());
//Set-->List
Set<String> set = new HashSet<String>(new ArrayList<String>());
//数组-->Set
String[] strs = {"AA","BB"};
Set<String> set2 = new HashSet<String>(Arrays.asList(strs));
System.out.println(set2);
//Set-->数组
Set<String> set3 = new HashSet<String>(Arrays.asList("PP","OO"));
String[] strSet = new String[set3.size()];
set3.toArray(strSet);
System.out.println(Arrays.toString(strSet));
//Map操作
Map<String, String> map = new HashMap<String, String>();
map.put("YYY", "UUU");
map.put("RRR", "TTT");
// 将键转化为Set
Set<String> mapKeySet = map.keySet();
// 将值转化为Set
Set<String> mapValuesSet = new HashSet<String>(map.values());
// 将值转化为List
List<String> mapValuesList = new ArrayList<String>(map.values());

}
}