Question

如何做Hashmap我有像

这样的值列表

{"tname":"Learning Ratio and Proportion Concepts and practice assessment","gname":"Sixth grade"},
{"tname":"Number System","gname":"Sixth grade"},
{"tname":"quations and expression","gname":"Seventh grade"},{"tname":"Geometry","gname":"Seventh grade"}

我想存储为

list<String>={"Sixth grade","Seventh grade"}

list(list<String>)={{"Learning Ratio and Proportion Concepts and practice assessment","Number System"},{"quations and expression","Geometry"}}

任何人都可以帮助我...

Answer 1

将ArrayList与HashMap一起使用

   HashMap<String,ArrayList<String[]>> map = new HashMap<String,ArrayList<String[]>>();

   ArrayList<String[]> theList1 = new ArrayList()<String[]>();

   theList1.add(new String[] {"Learning Ratio and Proportion Concepts and practice assessment","Sixth grade"});

   map.put("tname", theList1);

Answer 2

我猜你想存储每个年级所需的书籍。

  enum Grades
  {
    SIXTH_GRADE, SEVENTH_GRADE;
  }

  public static void main(String[] args) throws IOException
  {
    Map<Grades, List<String>> literature = new HashMap<Grades, List<String>>();
    literature.put(Grades.SIXTH_GRADE, new ArrayList<String>(Arrays.asList("Learning Ratio and Proportion Concepts and practice assessment","Number System")));
    literature.put(Grades.SEVENTH_GRADE, new ArrayList<String>(Arrays.asList("Equations and expression","Geometry")));

    // get books for 6th grade
    List<String> books6th = literature.get(Grades.SIXTH_GRADE);

    for (String book : books6th)
      System.out.println(book);

    // get books for 7th grade
    List<String> books7th = literature.get(Grades.SEVENTH_GRADE);

    Collection<List<String>> allBooks = literature.values(); // tname data
    Set<Grades> allGrades = literature.keySet(); // data associated with gname
  }

我甚至会考虑使用ISBN编号，价格等成员创建class Book。但这取决于您的使用案例。

我在这里使用了枚举，而不是字符串，所以地图不容易出错。 E. g。如果有人意外地写"6th grade"而不是"sixth grade"，当然你也可以使用字符串常量。

使用枚举，您可以使用EnumMap代替HashMap

Map<Grades, List<String>> literature = new EnumMap<Grades, List<String>>(Grades.class);。

如何使用hashmap存储值列表？使用以下格式

2 个答案: