Java集合转换【List<-->数组、List<-->Set、数组<-->Set、Map-->Set、Map-->List】

Java集合间的相互转换

下面代码演示了List<-->数组、List<-->Set、数组<-->Set、Map将键转化为Set、Map将值转化为Set、Map将值转化为List等集合常用转化操作。

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());

	}
}