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());

}

}