0. Utils

  • 字符串数组的排序:

    Set<String> set = new TreeSet<String>();
    Collections.addAll(set, args);  // args 为 String[] 类型
  • 数组复制:

    • system.arraycopy:必须明确自行建立一个数组对象,

      int[] arr1 = {1, 2, 3, 4, 5}; 
      int[] arr2 = new int[5];
      
      System.arraycopy(arr1, 0, arr2, 0, arr1.length);
    • Arrays.copyOf:可直接传回一个数组对象:

    int[] arr1 = {1, 2, 3, 4, 5}; 
    int[] arr2 = Arrays.copyOf(arr1, arr1.length);
    // 如果新数组的长度超过原数组的长度,则保留数组默认值
    int[] arr3 = Arrays.copyOf(arr1, 10);
            // 1 2 3 4 5 0 0 0 0 0

1. List <–> Array

  • list 实例转换为 String[],使用 list 的实例方法:toArray

    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[] => list,使用 Arrays 的静态方法 asList

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

2. Array => list => Set

  • 其实是先将 array 转换为 list 再转换为 set:

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

3. Map => Set/List

  • Map => List

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

    Set<String> targetSet = new HashSet<>(sourceMap.values());  
posted on 2018-06-10 19:22  未雨愁眸  阅读(171)  评论(0编辑  收藏  举报