JAVA集合之间的相互转换

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());  
  
    }  
}  

文章转自：http://jerval.iteye.com/blog/1001643